merge: display-management (Stages 0-5 §6A + keep-alive hardening + gaming-rig)

Merges display-mgmt-stage0 — the user-configurable virtual-display policy layer above the
per-compositor backends. On-glass validated (KWin .116 + Mutter .21; Windows compile-verified .173):

- Policy surface (keep_alive · topology · conflict · identity · layout · max) →
  display-settings.json, console-editable via /api/v1/display/{settings,state,release,layout} + a
  dedicated "Virtual displays" console section. All five axes enforced, not just stored.
- Lifecycle: pure state machine + Linux keep-alive pool (registry + DisplayLease ownership split),
  incl. keep_alive=forever/Pinned (freed via /display/release); topology extend/primary/exclusive
  (group-aware); per-client identity (KWin per-slot names → KDE scaling round-trips); mode_conflict
  admission (Windows default reject, single-capturer IDD); §6A multi-monitor (display groups +
  layout engine + console arrangement table — several clients as monitors of one desktop).
- Keep-alive reconnect hardened: same-client zombie preempt (never a 2nd display), deliberate-quit
  skip-linger (QUIT_CLOSE_CODE), tunable idle timeout (PUNKTFUNK_IDLE_TIMEOUT_MS).

Conflicts (packaging/{arch,debian}/README.md firewall docs): kept main's ufw/nft port commands +
the branch's --data-port documentation. build + clippy -D warnings + cargo test --workspace
(18 suites, 0 failed) green on the merged tree.

README.md

@@ -29,6 +29,11 @@ protocol, FEC, and crypto, linked into the host and every client over a stable C
 - **Your device's exact mode.** For each client that connects, the host spins up a virtual display
   sized to that device — 1080p60 to a laptop, 1440p120 to a desktop, 4K to a TV, all at once. No
   letterboxing, no scaling, no rearranging your real monitors.
+- **Displays you configure, not just create.** Keep a game's display (and the game) alive across
+  disconnects so a reconnect drops straight back in; make the stream your sole desktop or extend
+  alongside your monitors; let several devices become monitors of one desktop; keep each client's
+  scaling. One-click presets in the console — a dedicated couch box, a shared desktop, a multi-monitor
+  workstation. See [Virtual displays](docs-site/content/docs/virtual-displays.md).
 - **A real virtual display on Windows, too.** On Linux the host uses per-compositor virtual outputs;
   on Windows you get the same on-the-fly virtual display — at the client's exact mode, no physical
   monitor or dummy HDMI plug, even on the secure desktop (UAC / lock screen). It also has **its own

api/openapi.json

@@ -10,7 +10,7 @@
       "name": "MIT OR Apache-2.0",
       "identifier": "MIT OR Apache-2.0"
     },
-    "version": "0.6.0"
+    "version": "0.7.4"
   },
   "paths": {
     "/api/v1/clients": {
@@ -138,6 +138,224 @@
         }
       }
     },
+    "/api/v1/display/layout": {
+      "put": {
+        "tags": [
+          "display"
+        ],
+        "summary": "Arrange virtual displays",
+        "description": "Set the **manual** desktop arrangement — per-identity-slot `(x, y)` offsets so a multi-monitor\ngroup (§6A/§6B) comes back where the operator placed it. Persisted into the policy's layout block\nand switched to manual mode; applied from the next connect (a live group re-applies on its next\nacquire). Locks in the current effective behavior as explicit fields, so arranging displays never\nsilently changes keep-alive/topology/conflict/identity. See `design/display-management.md` §6.2.",
+        "operationId": "setDisplayLayout",
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/DisplayLayoutRequest"
+              }
+            }
+          },
+          "required": true
+        },
+        "responses": {
+          "200": {
+            "description": "Layout stored; the new settings state",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/DisplaySettingsState"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Missing or invalid bearer token",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "500": {
+            "description": "Layout could not be persisted",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
+    "/api/v1/display/release": {
+      "post": {
+        "tags": [
+          "display"
+        ],
+        "summary": "Release kept virtual displays",
+        "description": "Tear down lingering/pinned displays now — so a physical-screen user gets their screen back\nwithout waiting out the linger. `slot` releases one; omit it to release all kept displays.\nActive (streaming) displays are never torn down here (that is session control).",
+        "operationId": "releaseDisplay",
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/ReleaseDisplayRequest"
+              }
+            }
+          },
+          "required": true
+        },
+        "responses": {
+          "200": {
+            "description": "The number of kept displays released",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ReleaseDisplayResult"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Missing or invalid bearer token",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
+    "/api/v1/display/settings": {
+      "get": {
+        "tags": [
+          "display"
+        ],
+        "summary": "Display-management policy",
+        "description": "The stored virtual-display policy (lifecycle, topology, conflict handling, identity, layout),\nevery preset's expansion, and which options this build enforces yet. See\n`design/display-management.md`.",
+        "operationId": "getDisplaySettings",
+        "responses": {
+          "200": {
+            "description": "Stored policy + preset expansions + enforced options",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/DisplaySettingsState"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Missing or invalid bearer token",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          }
+        }
+      },
+      "put": {
+        "tags": [
+          "display"
+        ],
+        "summary": "Set the display-management policy",
+        "description": "Persists a new policy (validated + clamped) and applies it from the next connect/teardown — a\nrunning session keeps the display it opened on. `keep_alive: forever` (the gaming-rig preset) is\nhonored (the display is Pinned; free it via `POST /display/release`).",
+        "operationId": "setDisplaySettings",
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/DisplayPolicy"
+              }
+            }
+          },
+          "required": true
+        },
+        "responses": {
+          "200": {
+            "description": "Policy stored; the new state",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/DisplaySettingsState"
+                }
+              }
+            }
+          },
+          "400": {
+            "description": "Malformed policy body",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Missing or invalid bearer token",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "500": {
+            "description": "Policy could not be persisted",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
+    "/api/v1/display/state": {
+      "get": {
+        "tags": [
+          "display"
+        ],
+        "summary": "Live virtual displays",
+        "description": "The host's managed virtual displays right now — active (streaming), lingering (kept after\ndisconnect, counting down to teardown), or pinned (kept indefinitely). See\n`design/display-management.md`.",
+        "operationId": "getDisplayState",
+        "responses": {
+          "200": {
+            "description": "The live/kept virtual displays",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/DisplayStateResponse"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Missing or invalid bearer token",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/api/v1/gpus": {
       "get": {
         "tags": [
@@ -1601,6 +1819,99 @@
           "av1"
         ]
       },
+      "ApiDisplayInfo": {
+        "type": "object",
+        "description": "One live or kept virtual display.",
+        "required": [
+          "slot",
+          "backend",
+          "mode",
+          "state",
+          "sessions",
+          "group",
+          "display_index",
+          "x",
+          "y",
+          "topology"
+        ],
+        "properties": {
+          "backend": {
+            "type": "string",
+            "description": "Backend name (`pf-vdisplay`, `kwin`, …)."
+          },
+          "client": {
+            "type": [
+              "string",
+              "null"
+            ],
+            "description": "Short client label, when the owner tracks it."
+          },
+          "display_index": {
+            "type": "integer",
+            "format": "int32",
+            "description": "This display's ordinal within its group, in acquire order (0-based).",
+            "minimum": 0
+          },
+          "expires_in_ms": {
+            "type": [
+              "integer",
+              "null"
+            ],
+            "format": "int64",
+            "description": "Milliseconds until a lingering display is torn down (absent when active/pinned).",
+            "minimum": 0
+          },
+          "group": {
+            "type": "integer",
+            "format": "int32",
+            "description": "Display group (shared desktop) id — several displays with the same group form one desktop (§6A).",
+            "minimum": 0
+          },
+          "identity_slot": {
+            "type": [
+              "integer",
+              "null"
+            ],
+            "format": "int32",
+            "description": "Stable per-client identity slot keying persistent config + manual layout (absent = shared/anonymous).",
+            "minimum": 0
+          },
+          "mode": {
+            "type": "string",
+            "description": "`WIDTHxHEIGHT@HZ`."
+          },
+          "sessions": {
+            "type": "integer",
+            "format": "int32",
+            "description": "Live sessions holding the display.",
+            "minimum": 0
+          },
+          "slot": {
+            "type": "integer",
+            "format": "int64",
+            "description": "Stable-enough id for the `/display/release` `slot` argument.",
+            "minimum": 0
+          },
+          "state": {
+            "type": "string",
+            "description": "`active` | `lingering` | `pinned`."
+          },
+          "topology": {
+            "type": "string",
+            "description": "Effective topology for this display's group (`extend` | `primary` | `exclusive`)."
+          },
+          "x": {
+            "type": "integer",
+            "format": "int32",
+            "description": "Desktop-space top-left `x` (auto-row or the console's manual arrangement, §6.2)."
+          },
+          "y": {
+            "type": "integer",
+            "format": "int32",
+            "description": "Desktop-space top-left `y`."
+          }
+        }
+      },
       "ApiError": {
         "type": "object",
         "description": "Error envelope for every non-2xx response.",
@@ -1909,6 +2220,146 @@
           }
         }
       },
+      "DisplayLayoutRequest": {
+        "type": "object",
+        "description": "Request body for `setDisplayLayout`: per-identity-slot desktop offsets, keyed by the identity-slot\nid as a string (the same id `/display/state` reports as `identity_slot`).",
+        "properties": {
+          "positions": {
+            "type": "object",
+            "description": "`{\"<identity_slot>\": {\"x\": …, \"y\": …}}` — where each arranged display's top-left sits.",
+            "additionalProperties": {
+              "$ref": "#/components/schemas/Position"
+            },
+            "propertyNames": {
+              "type": "string"
+            }
+          }
+        }
+      },
+      "DisplayPolicy": {
+        "type": "object",
+        "description": "The user-facing display-management policy — what `display-settings.json` holds and what the mgmt\nAPI GETs/PUTs. When [`preset`](Self::preset) is not [`Preset::Custom`] the explicit fields are\nignored (the console writes one or the other); [`effective`](Self::effective) resolves both to a\nsingle [`EffectivePolicy`].",
+        "properties": {
+          "identity": {
+            "$ref": "#/components/schemas/Identity"
+          },
+          "keep_alive": {
+            "$ref": "#/components/schemas/KeepAlive"
+          },
+          "layout": {
+            "$ref": "#/components/schemas/Layout"
+          },
+          "max_displays": {
+            "type": "integer",
+            "format": "int32",
+            "description": "Upper bound on simultaneously-live virtual displays (clamped to `1..=16` on write).",
+            "minimum": 0
+          },
+          "mode_conflict": {
+            "$ref": "#/components/schemas/ModeConflict"
+          },
+          "preset": {
+            "$ref": "#/components/schemas/Preset"
+          },
+          "topology": {
+            "$ref": "#/components/schemas/Topology"
+          },
+          "version": {
+            "type": "integer",
+            "format": "int32",
+            "description": "Schema version (currently 1) — lets a future field addition migrate rather than reject.",
+            "minimum": 0
+          }
+        }
+      },
+      "DisplaySettingsState": {
+        "type": "object",
+        "description": "Full display-management state for the console: the stored policy, every preset's expansion, the\nresolved effective policy, and which options this build actually enforces yet (Stage 0 wires\nkeep-alive linger + topology; the rest are stored but not yet acted on).",
+        "required": [
+          "settings",
+          "configured",
+          "effective",
+          "presets",
+          "enforced"
+        ],
+        "properties": {
+          "configured": {
+            "type": "boolean",
+            "description": "True once a `display-settings.json` exists (the console has configured this host)."
+          },
+          "effective": {
+            "$ref": "#/components/schemas/EffectivePolicy",
+            "description": "The effective (preset-expanded) policy currently in force."
+          },
+          "enforced": {
+            "type": "array",
+            "items": {
+              "type": "string"
+            },
+            "description": "Option names this build enforces right now. All five axes are now acted on (keep_alive +\ntopology since Stage 0-2, identity Stage 3, mode_conflict Stage 4, layout Stage 5) — the console\nreads this to know which controls are live vs. \"coming soon\" (per-backend nuance, e.g. layout\nposition apply being KWin-only, is reported per display in `/display/state`)."
+          },
+          "presets": {
+            "type": "array",
+            "items": {
+              "$ref": "#/components/schemas/PresetInfo"
+            },
+            "description": "Every named preset and what it expands to (for the picker's preview)."
+          },
+          "settings": {
+            "$ref": "#/components/schemas/DisplayPolicy",
+            "description": "The stored policy (preset + custom fields), or the built-in default when unconfigured."
+          }
+        }
+      },
+      "DisplayStateResponse": {
+        "type": "object",
+        "description": "The host's managed virtual displays right now.",
+        "required": [
+          "displays"
+        ],
+        "properties": {
+          "displays": {
+            "type": "array",
+            "items": {
+              "$ref": "#/components/schemas/ApiDisplayInfo"
+            }
+          }
+        }
+      },
+      "EffectivePolicy": {
+        "type": "object",
+        "description": "The six resolved fields after preset expansion — what the lifecycle/registry and the Stage-0 call\nsites read, and what the mgmt API echoes as the \"currently in force\" policy. Pure output of\n[`DisplayPolicy::effective`].",
+        "required": [
+          "keep_alive",
+          "topology",
+          "mode_conflict",
+          "identity",
+          "layout",
+          "max_displays"
+        ],
+        "properties": {
+          "identity": {
+            "$ref": "#/components/schemas/Identity"
+          },
+          "keep_alive": {
+            "$ref": "#/components/schemas/KeepAlive"
+          },
+          "layout": {
+            "$ref": "#/components/schemas/Layout"
+          },
+          "max_displays": {
+            "type": "integer",
+            "format": "int32",
+            "minimum": 0
+          },
+          "mode_conflict": {
+            "$ref": "#/components/schemas/ModeConflict"
+          },
+          "topology": {
+            "$ref": "#/components/schemas/Topology"
+          }
+        }
+      },
       "GameEntry": {
         "type": "object",
         "description": "One title in the unified library, regardless of which store it came from.",
@@ -2099,6 +2550,72 @@
           }
         }
       },
+      "Identity": {
+        "type": "string",
+        "description": "Stable display identity, so desktop environments persist per-display config (KDE scaling). Stored\nat Stage 0; carriers wired from the identity stage.",
+        "enum": [
+          "shared",
+          "per-client",
+          "per-client-mode"
+        ]
+      },
+      "KeepAlive": {
+        "oneOf": [
+          {
+            "type": "object",
+            "description": "Tear the display down at session end (today's default on every backend but Windows, which\nlingers 10 s).",
+            "required": [
+              "mode"
+            ],
+            "properties": {
+              "mode": {
+                "type": "string",
+                "enum": [
+                  "off"
+                ]
+              }
+            }
+          },
+          {
+            "type": "object",
+            "description": "Keep the display for `seconds` after the last session leaves, then tear it down; a reconnect\ninside the window reuses it.",
+            "required": [
+              "seconds",
+              "mode"
+            ],
+            "properties": {
+              "mode": {
+                "type": "string",
+                "enum": [
+                  "duration"
+                ]
+              },
+              "seconds": {
+                "type": "integer",
+                "format": "int32",
+                "description": "Linger window in seconds.",
+                "minimum": 0
+              }
+            }
+          },
+          {
+            "type": "object",
+            "description": "Keep the display until host shutdown or an explicit release (the `Pinned` lifecycle state).\n**Not honored until the display-lifecycle stage** — rejected by the mgmt PUT at Stage 0.",
+            "required": [
+              "mode"
+            ],
+            "properties": {
+              "mode": {
+                "type": "string",
+                "enum": [
+                  "forever"
+                ]
+              }
+            }
+          }
+        ],
+        "description": "How long a virtual display (and, on gamescope's bare spawn, the nested session + its game)\nsurvives after the last client session detaches. Serialized as an object tagged on `mode`\n(`{\"mode\":\"off\"}` / `{\"mode\":\"duration\",\"seconds\":300}` / `{\"mode\":\"forever\"}`) so the web form\nand the OpenAPI schema stay simple."
+      },
       "LaunchSpec": {
         "type": "object",
         "description": "How the host would launch a title (consumed by the session launcher in a later step). Kept\nopen-ended so new stores slot in: `steam_appid` → `steam steam://rungameid/<value>`;\n`command` → run `<value>` nested in a gamescope session.",
@@ -2118,6 +2635,32 @@
           }
         }
       },
+      "Layout": {
+        "type": "object",
+        "description": "Group layout: the arrangement mode plus, for [`LayoutMode::Manual`], per-slot offsets keyed by\nidentity-slot id (string keys for stable JSON).",
+        "properties": {
+          "mode": {
+            "$ref": "#/components/schemas/LayoutMode"
+          },
+          "positions": {
+            "type": "object",
+            "additionalProperties": {
+              "$ref": "#/components/schemas/Position"
+            },
+            "propertyNames": {
+              "type": "string"
+            }
+          }
+        }
+      },
+      "LayoutMode": {
+        "type": "string",
+        "description": "How group members are arranged in the desktop coordinate space. Stored at Stage 0; applied from\nthe multi-monitor stage.",
+        "enum": [
+          "auto-row",
+          "manual"
+        ]
+      },
       "LocalSummary": {
         "type": "object",
         "description": "Non-sensitive host status for the local tray icon: counts and booleans only — no PIN values,\nno fingerprints, no device names. Served unauthenticated to LOOPBACK peers only (see\n`require_auth`): the bearer-token file is SYSTEM/Administrators-DACL'd on Windows, so the\nper-user tray process cannot authenticate — this narrow read-only route is its status source.",
@@ -2128,13 +2671,20 @@
           "paired_clients",
           "native_paired_clients",
           "pin_pending",
-          "pending_approvals"
+          "pending_approvals",
+          "kept_displays"
         ],
         "properties": {
           "audio_streaming": {
             "type": "boolean",
             "description": "True while the audio stream thread is running."
           },
+          "kept_displays": {
+            "type": "integer",
+            "format": "int32",
+            "description": "Virtual displays being KEPT with no live session — lingering (keep-alive window) or pinned\n(`keep_alive: forever`). Non-zero means a display (and, exclusive, your physical monitors) is\nheld; the tray surfaces it + a one-click release. Active (in-use) displays are not counted.",
+            "minimum": 0
+          },
           "native_paired_clients": {
             "type": "integer",
             "format": "int32",
@@ -2242,6 +2792,16 @@
           }
         }
       },
+      "ModeConflict": {
+        "type": "string",
+        "description": "Admission when a *different* client connects while a display/session is already live and asks for\na different mode. Stored at Stage 0; enforced from the mode-conflict admission stage.",
+        "enum": [
+          "separate",
+          "steal",
+          "join",
+          "reject"
+        ]
+      },
       "NativeClient": {
         "type": "object",
         "description": "A paired native (punktfunk/1) client.",
@@ -2439,6 +2999,88 @@
           }
         }
       },
+      "Position": {
+        "type": "object",
+        "description": "A desktop-space offset for a display (top-left origin).",
+        "required": [
+          "x",
+          "y"
+        ],
+        "properties": {
+          "x": {
+            "type": "integer",
+            "format": "int32"
+          },
+          "y": {
+            "type": "integer",
+            "format": "int32"
+          }
+        }
+      },
+      "Preset": {
+        "type": "string",
+        "description": "A named bundle of the fields below. `Custom` (the default) means the explicit fields rule; any\nother preset ignores the stored fields and expands to its own ([`DisplayPolicy::effective`]).",
+        "enum": [
+          "custom",
+          "default",
+          "gaming-rig",
+          "shared-desktop",
+          "hotdesk",
+          "workstation"
+        ]
+      },
+      "PresetInfo": {
+        "type": "object",
+        "description": "One preset's human-facing description + the fields it expands to, so the console can render a\npreset picker with an accurate \"what this does\" preview without hardcoding the expansion.",
+        "required": [
+          "id",
+          "summary",
+          "fields"
+        ],
+        "properties": {
+          "fields": {
+            "$ref": "#/components/schemas/EffectivePolicy",
+            "description": "The effective policy this preset expands to (the same fields a `custom` policy carries)."
+          },
+          "id": {
+            "type": "string",
+            "description": "The preset id (`default` | `gaming-rig` | `shared-desktop` | `hotdesk` | `workstation`)."
+          },
+          "summary": {
+            "type": "string",
+            "description": "One-line story shown next to the option."
+          }
+        }
+      },
+      "ReleaseDisplayRequest": {
+        "type": "object",
+        "description": "Request body for `releaseDisplay`.",
+        "properties": {
+          "slot": {
+            "type": [
+              "integer",
+              "null"
+            ],
+            "format": "int64",
+            "description": "Slot to release (see `state`); omit to release **all** kept displays.",
+            "minimum": 0
+          }
+        }
+      },
+      "ReleaseDisplayResult": {
+        "type": "object",
+        "description": "Result of a `/display/release`.",
+        "required": [
+          "released"
+        ],
+        "properties": {
+          "released": {
+            "type": "integer",
+            "description": "Number of kept displays torn down.",
+            "minimum": 0
+          }
+        }
+      },
       "RuntimeStatus": {
         "type": "object",
         "description": "Live host status (changes as clients launch/end sessions).",
@@ -2740,6 +3382,16 @@
             "example": "1234"
           }
         }
+      },
+      "Topology": {
+        "type": "string",
+        "description": "What the host does to the box's display topology while managed virtual displays are up.",
+        "enum": [
+          "auto",
+          "extend",
+          "primary",
+          "exclusive"
+        ]
       }
     },
     "securitySchemes": {
@@ -2763,6 +3415,10 @@
       "name": "gpu",
       "description": "GPU inventory and selection: list the host's GPUs, choose automatic or a preferred GPU, see the one in use"
     },
+    {
+      "name": "display",
+      "description": "Virtual-display management policy: lifecycle (keep-alive), topology (primary/exclusive), conflict handling, identity, and layout"
+    },
     {
       "name": "clients",
       "description": "Paired Moonlight client management"

clients/probe/src/main.rs

@@ -73,6 +73,14 @@ struct Args {
     /// `--rich-input-test` — drive the DualSense touchpad + motion over 0xCC (host needs
     /// `PUNKTFUNK_GAMEPAD=dualsense`); also logs the 0xCD HID-output feedback that comes back.
     rich_input_test: bool,
+    /// `--quit` — close the connection with the deliberate-quit code (`QUIT_CLOSE_CODE`) at end of
+    /// stream, so the host tears its virtual display down immediately (skips keep-alive linger). A
+    /// bare exit closes with code 0 → the host lingers for a reconnect. Tests the #2 quit path.
+    quit: bool,
+    /// `--seconds N` — cap the receive loop at N seconds, then end the session gracefully (reach the
+    /// `conn.close`). Without it the loop runs to the 120s cap. Lets a test bound a live-host stream so
+    /// the client-initiated close (with/without `--quit`) fires promptly.
+    seconds: Option<u64>,
     pin: Option<[u8; 32]>,
     /// `--remode WxHxFPS:SECS` — request this mode SECS seconds into the stream.
     remode: Option<(Mode, u32)>,
@@ -211,6 +219,8 @@ fn parse_args() -> Args {
         mic_burst: argv.iter().any(|a| a == "--mic-burst"),
         touch_test: argv.iter().any(|a| a == "--touch-test"),
         rich_input_test: argv.iter().any(|a| a == "--rich-input-test"),
+        quit: argv.iter().any(|a| a == "--quit"),
+        seconds: get("--seconds").and_then(|s| s.parse().ok()),
         pin,
         remode,
         pair: get("--pair").map(String::from),
@@ -1041,6 +1051,9 @@ async fn session(args: Args) -> Result<()> {
         let mut net_us_v: Vec<u64> = Vec::new();
         let mut last_rx = std::time::Instant::now();
         let started = std::time::Instant::now();
+        // Stream-duration cap: `--seconds N`, else the 120s default. Ending the loop here reaches the
+        // graceful `conn.close` below (with the deliberate-quit code if `--quit`).
+        let cap_secs = args.seconds.unwrap_or(120);
         // Adaptive-FEC loss window: publish a fresh estimate every 750 ms for the LossReport task.
         let mut last_loss_report = std::time::Instant::now();
         let (mut last_recovered, mut last_received, mut last_dropped) = (0u64, 0u64, 0u64);
@@ -1076,7 +1089,7 @@ async fn session(args: Args) -> Result<()> {
             {
                 break;
             }
-            if started.elapsed() > std::time::Duration::from_secs(120)
+            if started.elapsed() > std::time::Duration::from_secs(cap_secs)
                 || last_rx.elapsed() > std::time::Duration::from_secs(8)
             {
                 break;
@@ -1208,7 +1221,18 @@ async fn session(args: Args) -> Result<()> {
         }
     }
 
-    conn.close(0u32.into(), b"done");
+    // `--quit` closes with the deliberate-quit code so the host skips the keep-alive linger; a normal
+    // exit uses code 0 (an unwanted-disconnect close → the host lingers for a reconnect).
+    let close_code = if args.quit {
+        punktfunk_core::quic::QUIT_CLOSE_CODE
+    } else {
+        0
+    };
+    conn.close(close_code.into(), b"done");
+    // Flush the CONNECTION_CLOSE frame before we exit: without this the process can drop the endpoint
+    // before quinn sends the close, so the host waits out the idle timeout instead of seeing the close
+    // CODE promptly (deliberate-quit vs. code 0). Bounded so a stuck flush can't hang the probe.
+    let _ = tokio::time::timeout(std::time::Duration::from_secs(2), ep.wait_idle()).await;
     result
 }
 

crates/punktfunk-core/src/client.rs

@@ -179,6 +179,10 @@ pub struct NativeClient {
     /// Speed-test accumulator, shared with the data-plane pump + control task.
     probe: Arc<Mutex<ProbeState>>,
     shutdown: Arc<AtomicBool>,
+    /// Deliberate-quit flag: [`NativeClient::disconnect_quit`] sets it, so the worker closes the QUIC
+    /// connection with [`crate::quic::QUIT_CLOSE_CODE`] (a user "stop") instead of code 0 — telling the
+    /// host to skip the keep-alive linger. A plain drop leaves it false → an unwanted-disconnect close.
+    quit: Arc<AtomicBool>,
     /// Cumulative count of access units the reassembler gave up on (FEC couldn't recover), mirrored
     /// from the data-plane pump's `Session`. A client video loop watches this for increases to request
     /// a recovery keyframe under infinite GOP — the correct loss trigger, since unrecoverable loss
@@ -331,6 +335,7 @@ impl NativeClient {
         let (ctrl_tx, ctrl_rx) = tokio::sync::mpsc::unbounded_channel::<CtrlRequest>();
         let (ready_tx, ready_rx) = std::sync::mpsc::channel::<Result<Negotiated>>();
         let shutdown = Arc::new(AtomicBool::new(false));
+        let quit = Arc::new(AtomicBool::new(false));
         let mode_slot = Arc::new(std::sync::Mutex::new(mode));
         let probe = Arc::new(Mutex::new(ProbeState::default()));
         let frames_dropped = Arc::new(AtomicU64::new(0));
@@ -338,6 +343,7 @@ impl NativeClient {
 
         let host = host.to_string();
         let shutdown_w = shutdown.clone();
+        let quit_w = quit.clone();
         let mode_slot_w = mode_slot.clone();
         let probe_w = probe.clone();
         let frames_dropped_w = frames_dropped.clone();
@@ -388,6 +394,7 @@ impl NativeClient {
                     ctrl_tx: ctrl_tx_pump,
                     ready_tx,
                     shutdown: shutdown_w,
+                    quit: quit_w,
                     mode_slot: mode_slot_w,
                     probe: probe_w,
                     frames_dropped: frames_dropped_w,
@@ -430,6 +437,7 @@ impl NativeClient {
             ctrl_tx,
             probe,
             shutdown,
+            quit,
             worker: Some(worker),
             frames_dropped,
             hot_tids,
@@ -764,6 +772,15 @@ impl NativeClient {
             .send(rich)
             .map_err(|_| PunktfunkError::Closed)
     }
+
+    /// Signal a **deliberate quit** (a user "stop", not a network drop): the worker closes the QUIC
+    /// connection with [`crate::quic::QUIT_CLOSE_CODE`] instead of code 0, so the host tears the
+    /// session's virtual display down immediately and skips the keep-alive linger. Then requests
+    /// shutdown. A plain `drop` (without this) closes with code 0 → the host lingers for a reconnect.
+    pub fn disconnect_quit(&self) {
+        self.quit.store(true, Ordering::SeqCst);
+        self.shutdown.store(true, Ordering::SeqCst);
+    }
 }
 
 impl Drop for NativeClient {
@@ -802,6 +819,8 @@ struct WorkerArgs {
     ctrl_tx: tokio::sync::mpsc::UnboundedSender<CtrlRequest>,
     ready_tx: std::sync::mpsc::Sender<Result<Negotiated>>,
     shutdown: Arc<AtomicBool>,
+    /// Deliberate-quit flag (see [`NativeClient::quit`]): the worker closes with the quit code if set.
+    quit: Arc<AtomicBool>,
     mode_slot: Arc<std::sync::Mutex<Mode>>,
     probe: Arc<Mutex<ProbeState>>,
     frames_dropped: Arc<AtomicU64>,
@@ -838,6 +857,7 @@ async fn worker_main(args: WorkerArgs) {
         ctrl_tx,
         ready_tx,
         shutdown,
+        quit,
         mode_slot,
         probe,
         frames_dropped,
@@ -1210,5 +1230,12 @@ async fn worker_main(args: WorkerArgs) {
     })
     .await;
 
-    conn.close(0u32.into(), b"client closed");
+    // Deliberate quit (a user "stop") closes with the quit code → the host skips the keep-alive
+    // linger; a plain drop / disconnect closes with 0 → the host lingers so a reconnect can resume.
+    let close_code = if quit.load(Ordering::SeqCst) {
+        crate::quic::QUIT_CLOSE_CODE
+    } else {
+        0
+    };
+    conn.close(close_code.into(), b"client closed");
 }

crates/punktfunk-core/src/quic.rs

@@ -122,6 +122,13 @@ pub const VIDEO_CAP_444: u8 = 0x04;
 /// stage. Purely observability — never changes what the host encodes.
 pub const VIDEO_CAP_HOST_TIMING: u8 = 0x08;
 
+/// QUIC application error code a punktfunk/1 client closes the control connection with on a
+/// **deliberate quit** (a user "stop", not a network drop). The host reads it off the connection's
+/// `ApplicationClosed` reason and tears the session's virtual display down immediately, skipping the
+/// keep-alive linger; any other close reason (idle timeout, reset, a bare code 0) still lingers so a
+/// reconnect can resume. Shared so host + every client agree on the code.
+pub const QUIT_CLOSE_CODE: u32 = 0x51;
+
 /// [`Hello::video_codecs`] bit: the client can decode H.264 / AVC. The GPU-less **software**
 /// encode path (openh264) emits H.264, so a client that wants to stream from a software host MUST
 /// advertise this.
@@ -1743,20 +1750,31 @@ pub mod endpoint {
     /// every `KEEP_ALIVE` keeps the path warm. The interval sits well under `MAX_IDLE` so
     /// several keepalives can be lost back-to-back (a wifi roam, a brief blip) without a false
     /// close, while a genuinely dead peer is still detected within `MAX_IDLE`.
+    /// The default control-connection idle timeout (disconnect-detection latency). A vanished client
+    /// is declared dead within this window — the Windows IDD-push path needs it short so a RECONNECT
+    /// recreates a fresh virtual monitor instead of joining the still-lingering old session; the Linux
+    /// path pairs it with the same-client reconnect preempt. Host-tunable via `server_with_identity_idle`.
+    pub const DEFAULT_IDLE_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(8);
+
     fn stream_transport() -> Arc<quinn::TransportConfig> {
+        stream_transport_idle(DEFAULT_IDLE_TIMEOUT)
+    }
+
+    /// Transport config with a caller-chosen idle timeout (disconnect-detection latency). The
+    /// keep-alive interval tracks it at half the idle window (capped at the default 4s), so a live
+    /// path is PINGed at least twice per window and a single lost PING (wifi roam / brief blip) won't
+    /// false-close. `idle` is clamped to a ≥1s floor so a misconfigured tiny value can't tear live
+    /// sessions down. Active sessions are unaffected either way: video keeps the connection live and
+    /// the keep-alive holds it open through quiet control periods.
+    fn stream_transport_idle(idle: std::time::Duration) -> Arc<quinn::TransportConfig> {
         use std::time::Duration;
-        // 8s idle (was 20s): a vanished client is declared dead within 8s instead of 20, so its
+        let idle = idle.max(Duration::from_secs(1));
-        // session tears down promptly — which the Windows IDD-push path needs so a RECONNECT recreates
+        let keep_alive = (idle / 2).min(Duration::from_secs(4));
-        // a fresh virtual monitor (a reused monitor's IddCx swap-chain dies) instead of joining the
-        // still-lingering old session. Active sessions are unaffected: video keeps the connection live,
-        // and the 4s keep-alive holds it open through quiet control periods.
-        const MAX_IDLE: Duration = Duration::from_secs(8);
-        const KEEP_ALIVE: Duration = Duration::from_secs(4);
         let mut t = quinn::TransportConfig::default();
         t.max_idle_timeout(Some(
-            quinn::IdleTimeout::try_from(MAX_IDLE).expect("8s is a valid QUIC idle timeout"),
+            quinn::IdleTimeout::try_from(idle).expect("clamped idle timeout is a valid QUIC value"),
         ));
-        t.keep_alive_interval(Some(KEEP_ALIVE));
+        t.keep_alive_interval(Some(keep_alive));
         Arc::new(t)
     }
 
@@ -1767,23 +1785,36 @@ pub mod endpoint {
             .map_err(|e| anyhow_result::Error::msg(format!("self-signed cert: {e}")))?;
         let cert_der = rustls::pki_types::CertificateDer::from(cert.cert);
         let key_der = rustls::pki_types::PrivatePkcs8KeyDer::from(cert.key_pair.serialize_der());
-        server_from_der(cert_der, key_der.into(), addr)
+        server_from_der(cert_der, key_der.into(), addr, DEFAULT_IDLE_TIMEOUT)
     }
 
     /// Server endpoint from a persisted PEM identity (certificate + PKCS#8 private key) —
     /// the host's long-lived self-signed cert, so the fingerprint clients pin is stable
-    /// across restarts.
+    /// across restarts. Uses the [`DEFAULT_IDLE_TIMEOUT`]; see [`server_with_identity_idle`] to tune it.
     pub fn server_with_identity(
         addr: std::net::SocketAddr,
         cert_pem: &str,
         key_pem: &str,
+    ) -> anyhow_result::Result<quinn::Endpoint> {
+        server_with_identity_idle(addr, cert_pem, key_pem, DEFAULT_IDLE_TIMEOUT)
+    }
+
+    /// Like [`server_with_identity`] but with a host-chosen control-connection idle timeout — the
+    /// disconnect-detection latency (how long a vanished client takes to be declared dead). Shorter =
+    /// faster teardown/linger of a dropped session; the value is clamped to a ≥1s floor and its
+    /// keep-alive scales with it so a live session never false-closes.
+    pub fn server_with_identity_idle(
+        addr: std::net::SocketAddr,
+        cert_pem: &str,
+        key_pem: &str,
+        idle: std::time::Duration,
     ) -> anyhow_result::Result<quinn::Endpoint> {
         use rustls::pki_types::pem::PemObject;
         let cert_der = rustls::pki_types::CertificateDer::from_pem_slice(cert_pem.as_bytes())
             .map_err(|e| anyhow_result::Error::msg(format!("cert pem: {e}")))?;
         let key_der = rustls::pki_types::PrivateKeyDer::from_pem_slice(key_pem.as_bytes())
             .map_err(|e| anyhow_result::Error::msg(format!("key pem: {e}")))?;
-        server_from_der(cert_der, key_der, addr)
+        server_from_der(cert_der, key_der, addr, idle)
     }
 
     /// Fixed ALPN for the punktfunk/1 QUIC handshake. Pinning it rejects a cross-protocol peer at the
@@ -1796,6 +1827,7 @@ pub mod endpoint {
         cert_der: rustls::pki_types::CertificateDer<'static>,
         key_der: rustls::pki_types::PrivateKeyDer<'static>,
         addr: std::net::SocketAddr,
+        idle: std::time::Duration,
     ) -> anyhow_result::Result<quinn::Endpoint> {
         let _ = rustls::crypto::ring::default_provider().install_default();
         // Client auth is OFFERED but optional: a client that presents its self-signed
@@ -1810,7 +1842,7 @@ pub mod endpoint {
         let quic_cfg = quinn::crypto::rustls::QuicServerConfig::try_from(rustls_cfg)
             .map_err(|e| anyhow_result::Error::msg(format!("quic server config: {e}")))?;
         let mut server_config = quinn::ServerConfig::with_crypto(Arc::new(quic_cfg));
-        server_config.transport_config(stream_transport()); // keep-alive — see stream_transport
+        server_config.transport_config(stream_transport_idle(idle)); // keep-alive — see stream_transport_idle
         Ok(quinn::Endpoint::server(server_config, addr)?)
     }
 

crates/punktfunk-core/src/transport/udp.rs

@@ -416,7 +416,14 @@ impl UdpTransport {
     /// Bind `local` and `connect` to `peer`, so `send`/`recv` need no address and the
     /// kernel filters to this peer. Non-blocking, matching the [`Transport`] contract.
     pub fn connect(local: &str, peer: &str) -> std::io::Result<Self> {
-        let socket = UdpSocket::bind(local)?;
+        Self::from_socket(UdpSocket::bind(local)?, peer)
+    }
+
+    /// Adopt an already-bound socket for the data plane: `connect` it to `peer`, tune buffers +
+    /// QoS, go non-blocking. Lets the host bind the data port up front (e.g. a fixed `--data-port`)
+    /// and keep the *same* socket from handshake through streaming — no drop-then-rebind window in
+    /// which a concurrent session could steal a fixed port.
+    pub fn from_socket(socket: UdpSocket, peer: &str) -> std::io::Result<Self> {
         socket.connect(peer)?;
         super::qos::grow_socket_buffers(&socket);
         // The native data plane is video-dominant — tag it as the video class (opt-in via
@@ -438,7 +445,16 @@ impl UdpTransport {
         fallback_peer: &str,
         punch_timeout: std::time::Duration,
     ) -> std::io::Result<(Self, bool)> {
-        let socket = UdpSocket::bind(local)?;
+        Self::from_socket_punch(UdpSocket::bind(local)?, fallback_peer, punch_timeout)
+    }
+
+    /// [`connect_via_punch`](Self::connect_via_punch) on an already-bound socket — see
+    /// [`from_socket`](Self::from_socket) for why the host binds the data port up front.
+    pub fn from_socket_punch(
+        socket: UdpSocket,
+        fallback_peer: &str,
+        punch_timeout: std::time::Duration,
+    ) -> std::io::Result<(Self, bool)> {
         socket.set_read_timeout(Some(punch_timeout))?;
         let deadline = std::time::Instant::now() + punch_timeout;
         let mut buf = [0u8; 64];

crates/punktfunk-host/src/gamestream/apps.rs

@@ -170,18 +170,26 @@ pub fn appasset_bytes(appid: u32) -> Option<(Vec<u8>, String)> {
 /// Render the GameStream `/applist` XML. `IsHdrSupported` reflects whether the host can actually deliver
 /// HDR (HEVC Main10 / PQ) for a title — host-wide today ([`crate::gamestream::host_hdr_capable`]); when
 /// true, Moonlight offers its per-app HDR toggle.
+///
+/// The document is emitted **COMPACT — no whitespace between elements** — deliberately, to match
+/// Sunshine/GFE. Moonlight-Android's `getAppListByReader` calls `appList.getLast()` on *every* XML
+/// text node before it checks the current tag, and only fills `appList` on an `<App>` start tag. A
+/// pretty-print newline between `<root>` and the first `<App>` is a whitespace text node while
+/// `appList` is still empty → `NoSuchElementException` → the Android app hard-crashes on host click.
+/// (iOS/macOS parse via moonlight-common-c/expat and are unaffected; `serverinfo`/pairing use the
+/// named-tag `getXmlString` scan, so their whitespace is harmless.) Keep this whitespace-free.
 pub fn applist_xml() -> String {
     let hdr = u8::from(crate::gamestream::host_hdr_capable());
     let mut xml =
-        String::from("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n<root status_code=\"200\">\n");
+        String::from("<?xml version=\"1.0\" encoding=\"utf-8\"?><root status_code=\"200\">");
     for app in catalog() {
         xml.push_str(&format!(
-            "<App>\n<IsHdrSupported>{hdr}</IsHdrSupported>\n<AppTitle>{}</AppTitle>\n<ID>{}</ID>\n</App>\n",
+            "<App><IsHdrSupported>{hdr}</IsHdrSupported><AppTitle>{}</AppTitle><ID>{}</ID></App>",
             xml_escape(&app.title),
             app.id
         ));
     }
-    xml.push_str("</root>\n");
+    xml.push_str("</root>");
     xml
 }
 
@@ -249,4 +257,27 @@ mod tests {
         assert!(xml.starts_with("<?xml"));
         assert_eq!(xml.matches("<App>").count(), xml.matches("</App>").count());
     }
+
+    /// Regression: the applist MUST be whitespace-free between elements. Moonlight-Android's
+    /// `getAppListByReader` calls `appList.getLast()` on every text node before an `<App>` has been
+    /// pushed, so a pretty-print newline between `<root>` and the first `<App>` crashes the app
+    /// (`NoSuchElementException`). Reproduced on 2 Android phones; iOS/macOS (moonlight-common-c)
+    /// were unaffected. Keep `applist_xml` compact like Sunshine/GFE.
+    #[test]
+    fn applist_xml_has_no_interelement_whitespace() {
+        let xml = applist_xml();
+        // <root> is immediately followed by the first <App> — no whitespace text node while the
+        // parser's app list is still empty.
+        assert!(
+            xml.contains("status_code=\"200\"><App>"),
+            "no whitespace between <root> and the first <App>: {xml}"
+        );
+        // No pretty-print newlines anywhere in the element stream, and no whitespace-only text
+        // nodes between any adjacent tags.
+        assert!(!xml.contains('\n'), "applist must contain no newlines: {xml}");
+        assert!(
+            !xml.contains("> <"),
+            "applist must contain no inter-element spaces: {xml}"
+        );
+    }
 }

crates/punktfunk-host/src/gamestream/mod.rs

@@ -108,6 +108,11 @@ pub struct LaunchSession {
     /// unpaired RTSP peer cannot ride a paired client's launch (security-review 2026-06-28 #4).
     /// `None` if the address could not be captured (then RTSP falls back to launch-present only).
     pub peer_ip: Option<std::net::IpAddr>,
+    /// SHA-256 cert fingerprint of the paired client that owns this session — mode-conflict admission
+    /// (Stage 4) compares it against a launching client to tell a same-client re-launch (always
+    /// allowed) from a DIFFERENT client (subject to the `mode_conflict` policy). `[u8; 32]` keeps
+    /// [`LaunchSession`] `Copy`; `None` when the peer cert couldn't be read.
+    pub owner_fp: Option<[u8; 32]>,
 }
 
 /// Shared control-plane state used as the axum app state.

crates/punktfunk-host/src/gamestream/nvhttp.rs

@@ -126,15 +126,57 @@ async fn h_launch(
     peer: Option<Extension<PeerCertFingerprint>>,
     addr: Option<Extension<PeerAddr>>,
     Query(q): Query<HashMap<String, String>>,
-) -> impl IntoResponse {
+) -> Response {
     if !peer_is_paired(&peer, &st) {
         tracing::warn!("launch rejected — client is not paired");
-        return xml(error_xml());
+        return xml(error_xml()).into_response();
     }
+    let req_fp: Option<[u8; 32]> = match &peer {
+        Some(Extension(PeerCertFingerprint(Some(fp)))) => {
+            hex::decode(fp).ok().and_then(|v| <[u8; 32]>::try_from(v).ok())
+        }
+        _ => None,
+    };
+
+    // Mode-conflict ADMISSION (Stage 4) — GameStream is single-session (`st.launch`), so a DIFFERENT
+    // paired client launching while a session is live is governed by `mode_conflict` (see
+    // [`gamestream_admission`]). Snapshot the live owner + mode (Copy) so the lock isn't held over it.
+    let mut forced_mode: Option<(u32, u32, u32)> = None;
+    {
+        let live = st
+            .launch
+            .lock()
+            .unwrap()
+            .as_ref()
+            .map(|s| (s.owner_fp, (s.width, s.height, s.fps)));
+        // Same Windows default as the native path (separate → reject; see `effective_conflict`) so a
+        // 2nd Moonlight client gets a clean 503 rather than wedging the shared monitor's capture.
+        let conflict = crate::vdisplay::admission::effective_conflict();
+        match gamestream_admission(live, req_fp, conflict) {
+            GsDecision::Serve => {}
+            GsDecision::Join((w, h, f)) => {
+                forced_mode = Some((w, h, f));
+                tracing::info!("GameStream launch JOIN — admitting at the live session's mode {w}x{h}@{f}");
+            }
+            GsDecision::Reject => {
+                tracing::warn!(
+                    "GameStream launch REJECTED — host busy (mode_conflict=reject, session owned by another client)"
+                );
+                return (StatusCode::SERVICE_UNAVAILABLE, xml(error_xml())).into_response();
+            }
+        }
+    }
+
     match launch(&st, &q) {
         Ok(mut session) => {
             // Bind the (unauthenticated) RTSP/UDP media plane to this paired client's source IP.
             session.peer_ip = addr.map(|Extension(PeerAddr(a))| a.ip());
+            session.owner_fp = req_fp;
+            if let Some((w, h, f)) = forced_mode {
+                session.width = w;
+                session.height = h;
+                session.fps = f;
+            }
             *st.launch.lock().unwrap() = Some(session);
             tracing::info!(
                 w = session.width,
@@ -144,11 +186,11 @@ async fn h_launch(
                 "launch — session created; RTSP at rtsp://{}:{RTSP_PORT}",
                 st.host.local_ip
             );
-            xml(session_url_xml(&st, "gamesession"))
+            xml(session_url_xml(&st, "gamesession")).into_response()
         }
         Err(e) => {
             tracing::warn!(error = %format!("{e:#}"), "launch failed");
-            xml(error_xml())
+            xml(error_xml()).into_response()
         }
     }
 }
@@ -210,7 +252,8 @@ fn launch(_st: &AppState, q: &HashMap<String, String>) -> Result<LaunchSession>
         height,
         fps,
         appid,
-        peer_ip: None, // set by `h_launch` from the verified HTTPS peer address
+        peer_ip: None,  // set by `h_launch` from the verified HTTPS peer address
+        owner_fp: None, // set by `h_launch` from the verified HTTPS peer cert fingerprint
     })
 }
 
@@ -223,6 +266,48 @@ fn parse_mode(mode: &str) -> Option<(u32, u32, u32)> {
     Some((w, h, fps))
 }
 
+/// A live GameStream session's `(owner cert fingerprint, mode)` snapshot for [`gamestream_admission`].
+type LiveGs = (Option<[u8; 32]>, (u32, u32, u32));
+
+/// The outcome of [`gamestream_admission`].
+enum GsDecision {
+    /// Proceed with the launch (no live session, a same-client re-launch, or `steal`/`separate`
+    /// taking over the single session).
+    Serve,
+    /// Serve at the live session's mode (`join` — honest-downgrade).
+    Join((u32, u32, u32)),
+    /// Refuse with a 503 (`reject`).
+    Reject,
+}
+
+/// The GameStream single-session mode-conflict decision (Stage 4, pure so it's unit-tested). `live`
+/// is the currently-live session's `(owner_fp, mode)` (`None` ⇒ no session live). No session or a
+/// same-client re-launch ⇒ `Serve`; a DIFFERENT client launching applies `policy` — `reject` ⇒
+/// `Reject`, `join` ⇒ `Join` the live mode, `steal`/`separate` (GameStream has no separate) ⇒ `Serve`
+/// (take over the one session).
+fn gamestream_admission(
+    live: Option<LiveGs>,
+    req_fp: Option<[u8; 32]>,
+    policy: crate::vdisplay::policy::ModeConflict,
+) -> GsDecision {
+    use crate::vdisplay::policy::ModeConflict;
+    let Some((owner, mode)) = live else {
+        return GsDecision::Serve;
+    };
+    let different = match (owner, req_fp) {
+        (Some(o), Some(r)) => o != r,
+        _ => true, // unknown owner or anonymous requester → treat as a different client
+    };
+    if !different {
+        return GsDecision::Serve;
+    }
+    match policy {
+        ModeConflict::Reject => GsDecision::Reject,
+        ModeConflict::Join => GsDecision::Join(mode),
+        ModeConflict::Steal | ModeConflict::Separate => GsDecision::Serve,
+    }
+}
+
 fn session_url_xml(st: &AppState, tag: &str) -> String {
     format!(
         "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n<root status_code=\"200\">\n<sessionUrl0>rtsp://{}:{RTSP_PORT}</sessionUrl0>\n<{tag}>1</{tag}>\n</root>\n",
@@ -349,4 +434,43 @@ mod tests {
             "a non-pinned cert stays rejected"
         );
     }
+
+    #[test]
+    fn gamestream_admission_policy_matrix() {
+        use crate::vdisplay::policy::ModeConflict;
+        let (a, b) = ([1u8; 32], [2u8; 32]);
+        let live = Some((Some(a), (2560, 1440, 120)));
+        // No live session → always Serve.
+        assert!(matches!(
+            gamestream_admission(None, Some(b), ModeConflict::Reject),
+            GsDecision::Serve
+        ));
+        // Same-client re-launch → Serve regardless of policy.
+        assert!(matches!(
+            gamestream_admission(live, Some(a), ModeConflict::Reject),
+            GsDecision::Serve
+        ));
+        // A DIFFERENT client applies the policy.
+        assert!(matches!(
+            gamestream_admission(live, Some(b), ModeConflict::Reject),
+            GsDecision::Reject
+        ));
+        assert!(matches!(
+            gamestream_admission(live, Some(b), ModeConflict::Join),
+            GsDecision::Join((2560, 1440, 120))
+        ));
+        assert!(matches!(
+            gamestream_admission(live, Some(b), ModeConflict::Steal),
+            GsDecision::Serve
+        ));
+        assert!(matches!(
+            gamestream_admission(live, Some(b), ModeConflict::Separate),
+            GsDecision::Serve
+        ));
+        // Anonymous requester (no cert presented) is treated as a different client.
+        assert!(matches!(
+            gamestream_admission(live, None, ModeConflict::Reject),
+            GsDecision::Reject
+        ));
+    }
 }

crates/punktfunk-host/src/gamestream/stream.rs

@@ -286,13 +286,19 @@ fn open_gs_virtual_source(
             std::sync::atomic::AtomicBool::new(false),
         ))
     });
-    let vout = vd
+    let vout = crate::vdisplay::registry::acquire(
-        .create(punktfunk_core::Mode {
+        &mut vd,
+        punktfunk_core::Mode {
             width: cfg.width,
             height: cfg.height,
             refresh_hz: cfg.fps,
-        })
+        },
-        .context("create virtual output at client resolution")?;
+        // GameStream's deliberate quit is the Moonlight "Quit App" (nvhttp `h_cancel`), not a QUIC
+        // close code — wiring it to skip-linger is a follow-up, so this path keeps normal keep-alive
+        // (a fresh, never-set flag).
+        std::sync::Arc::new(std::sync::atomic::AtomicBool::new(false)),
+    )
+    .context("create virtual output at client resolution")?;
     // HDR: pass the negotiated `cfg.hdr` (client asked for HDR AND the host can deliver it). On the
     // Windows IDD-push path this proactively enables advanced color on the virtual display so a Main10
     // PQ stream flows even from an SDR desktop; an already-HDR desktop streams PQ regardless (the
@@ -397,6 +403,68 @@ fn sendmmsg_all(sock: &UdpSocket, pkts: &[Vec<u8>]) -> std::io::Result<()> {
     Ok(())
 }
 
+/// Pacing layout for one frame's `n` packets (`n >= 1`): `(chunk_size, steps)`. The chunk grows
+/// with the frame so the number of paced bursts — each ending in a `thread::sleep` — never exceeds
+/// `MAX_PACE_STEPS`. A fixed 16-packet chunk let the step count scale with bitrate (~38 for a
+/// 4K/250Mbps frame's ~600 packets); the accumulated sub-ms sleep overshoot on the non-RT send
+/// thread then blew the per-frame budget and backed the handoff queue up. Bounding the steps keeps
+/// microburst shaping at low bitrate while making overshoot negligible and bitrate-independent.
+fn pace_layout(n: usize) -> (usize, usize) {
+    const MIN_PACE_CHUNK: usize = 16;
+    const MAX_PACE_STEPS: usize = 12;
+    let chunk_sz = MIN_PACE_CHUNK.max(n.div_ceil(MAX_PACE_STEPS));
+    let steps = n.div_ceil(chunk_sz); // ≤ MAX_PACE_STEPS
+    (chunk_sz, steps)
+}
+
+/// One encoded frame handed from the encode loop to the packetizer thread: the frame's access
+/// units (owned buffers, each with its frame type) plus the shared 90 kHz RTP timestamp. FEC
+/// packetization runs on the packetizer thread — off the encode loop — so it never serializes
+/// behind encode (measured ~3 ms/frame at 4K, which capped GameStream's frame rate well below what
+/// the encoder alone can sustain).
+struct RawFrame {
+    aus: Vec<(Vec<u8>, FrameType)>,
+    ts: u32,
+}
+
+/// Packetizer thread: turns each [`RawFrame`]'s access units into wire datagrams (data + Reed–Solomon
+/// FEC parity shards) via the stateful [`VideoPacketizer`], then hands the batch to the paced sender.
+/// It sits between encode and send so the FEC never blocks the encode loop. Backpressure: the hand-off
+/// to the sender BLOCKS, so if the paced sender falls behind, the packetizer stalls and the
+/// encode→packetizer queue fills — the encode loop then drops the newest frame (see the loop) rather
+/// than stalling. Tallies goodput (bytes handed to the wire) into `goodput` for the encode loop's stats
+/// window. Exits when either neighbor's channel closes (session teardown / client gone).
+fn spawn_packetizer(
+    rx: std::sync::mpsc::Receiver<RawFrame>,
+    tx: std::sync::mpsc::SyncSender<PacketBatch>,
+    mut pk: VideoPacketizer,
+    goodput: Arc<std::sync::atomic::AtomicU64>,
+) -> Result<()> {
+    std::thread::Builder::new()
+        .name("punktfunk-pkt".into())
+        .spawn(move || {
+            // Above-normal, like the send thread — this stage is on the per-frame critical path.
+            crate::punktfunk1::boost_thread_priority(false);
+            while let Ok(frame) = rx.recv() {
+                let mut batch: PacketBatch = Vec::new();
+                for (au, ft) in frame.aus {
+                    batch.extend(pk.packetize(&au, ft, frame.ts));
+                }
+                if batch.is_empty() {
+                    continue;
+                }
+                let bytes: u64 = batch.iter().map(|p| p.len() as u64).sum();
+                // Blocking send: propagates the paced sender's backpressure upstream (see above).
+                if tx.send(batch).is_err() {
+                    break; // sender exited (client gone)
+                }
+                goodput.fetch_add(bytes, std::sync::atomic::Ordering::Relaxed);
+            }
+        })
+        .context("spawn packetizer thread")?;
+    Ok(())
+}
+
 /// Dedicated send thread: one [`PacketBatch`] per frame arrives on `rx`; its packets go out in
 /// `sendmmsg` chunks, paced so the frame's data spreads over ~3/4 of the frame interval
 /// (microburst shaping at chunk granularity — a real link drops line-rate bursts; the encode
@@ -414,8 +482,14 @@ fn spawn_sender(
             // Transmit thread: above-normal, matching the native path's send thread (includes the
             // Windows session tuning/MMCSS this used to call directly; adds the Linux nice -5).
             crate::punktfunk1::boost_thread_priority(false);
-            // Chunk pacing: 16 packets per burst, bursts spread across the send budget.
+            // Chunk pacing: spread the frame's packets across the send budget in a BOUNDED number
-            const PACE_CHUNK: usize = 16;
+            // of bursts. A fixed 16-packet chunk made the burst count scale with bitrate (~38 for a
+            // 4K/250Mbps frame's ~600 packets), and each burst ends in a `thread::sleep`; on this
+            // non-RT send thread those sub-ms sleeps overshoot, and ~38 per frame blew the 12.5ms
+            // budget past the 16.67ms frame interval — backing the depth-2 handoff queue up and
+            // dropping ~half the frames ("send queue full"). Capping the step count keeps the
+            // microburst shaping (a real link drops line-rate bursts) while making per-frame sleep
+            // overshoot negligible and independent of bitrate.
             let budget = frame_interval.mul_f32(0.75);
             let mut rng = rand::thread_rng();
             let mut sent: u64 = 0;
@@ -434,17 +508,21 @@ fn spawn_sender(
                 if n == 0 {
                     continue;
                 }
-                let per_chunk = budget.mul_f64((PACE_CHUNK as f64 / n as f64).min(1.0));
+                // Chunk size + step count, bounded so a high-bitrate frame doesn't fan out into
+                // dozens of sleeps. Each step gets an equal slice of the budget (total pacing time
+                // == budget regardless of n).
+                let (chunk_sz, steps) = pace_layout(n);
+                let per_step = budget.mul_f64(1.0 / steps as f64);
                 let start = Instant::now();
-                for (i, chunk) in batch.chunks(PACE_CHUNK).enumerate() {
+                for (i, chunk) in batch.chunks(chunk_sz).enumerate() {
                     if let Err(e) = sendmmsg_all(&sock, chunk) {
                         tracing::info!(error = %e, sent, "video: client unreachable — stopping stream");
                         running.store(false, Ordering::SeqCst);
                         return;
                     }
                     sent += chunk.len() as u64;
-                    // Sleep toward the next chunk's deadline; skip sub-500µs sleeps (jitter).
+                    // Sleep toward the next step's deadline; skip sub-500µs sleeps (jitter).
-                    let target = start + per_chunk.mul_f64((i + 1) as f64);
+                    let target = start + per_step.mul_f64((i + 1) as f64);
                     if let Some(ahead) = target.checked_duration_since(Instant::now()) {
                         if ahead >= Duration::from_micros(500) {
                             std::thread::sleep(ahead);
@@ -518,7 +596,7 @@ fn stream_body(
         .ok()
         .and_then(|v| v.parse().ok())
         .unwrap_or(20);
-    let mut pk = VideoPacketizer::new(cfg.packet_size, fec_pct, cfg.min_fec);
+    let pk = VideoPacketizer::new(cfg.packet_size, fec_pct, cfg.min_fec);
 
     // Pace at the client's negotiated frame rate, re-encoding the last captured frame when the
     // compositor produced no new one. Compositors only emit frames on damage, so a static or
@@ -538,9 +616,15 @@ fn stream_body(
     let mut sent_batches: u64 = 0;
     let mut dropped_batches: u64 = 0;
 
-    // The send thread: one frame's batch at a time over a small bounded queue. Depth 2 means a
+    // Three-stage pipeline so FEC packetization never blocks encode: `encode loop → [raw AUs] →
-    // slow send can buffer one frame while the next encodes; beyond that the NEWEST batch is
+    // packetizer (FEC/RS) → [wire batch] → paced sender`, each stage on its own thread joined by a
-    // dropped (the client recovers via FEC/RFI) rather than ever stalling the encode loop.
+    // depth-2 bounded queue. Depth 2 means a slow stage can buffer one frame while the next is
+    // produced; beyond that the NEWEST frame is dropped (the client recovers via FEC/RFI) rather than
+    // stalling the encode loop. Backpressure chains up: a slow sender blocks the packetizer, which
+    // fills the encode→packetizer queue, which makes the encode loop drop — encode itself never
+    // waits. Goodput (bytes handed to the wire) is tallied by the packetizer into `goodput`, read at
+    // the encode loop's 1 s stats boundary (the old inline batch-byte sum moved with packetization).
+    let goodput = Arc::new(std::sync::atomic::AtomicU64::new(0));
     let (batch_tx, batch_rx) = std::sync::mpsc::sync_channel::<PacketBatch>(2);
     spawn_sender(
         sock.try_clone().context("clone video socket")?,
@@ -549,12 +633,14 @@ fn stream_body(
         running.clone(),
         drop_pct,
     )?;
+    let (raw_tx, raw_rx) = std::sync::mpsc::sync_channel::<RawFrame>(2);
+    spawn_packetizer(raw_rx, batch_tx, pk, goodput.clone())?;
 
     // Per-stage timing (PUNKTFUNK_PERF=1): max µs/stage per second + unique vs re-encoded frames,
     // to pinpoint stalls. `unique` counts genuinely-new captured frames (vs re-encoded holds).
     let perf = crate::config::config().perf;
-    let (mut mx_cap, mut mx_enc, mut mx_pkt, mut mx_send, mut mx_pkts, mut uniq) =
+    let (mut mx_cap, mut mx_enc, mut mx_pkt, mut mx_send, mut uniq) =
-        (0u128, 0u128, 0u128, 0u128, 0usize, 0u32);
+        (0u128, 0u128, 0u128, 0u128, 0u32);
     // Web-console stats accumulation (active when `perf` OR a capture is armed): per-stage vectors
     // for p50/p99, the goodput bytes queued to the sender this window, the previous window's
     // dropped-frame count for delta computation, and the registration id cached on the first sample.
@@ -566,7 +652,6 @@ fn stream_body(
     let mut sid: Option<u32> = None;
     let (mut v_cap, mut v_enc, mut v_pkt, mut v_send): (Vec<u32>, Vec<u32>, Vec<u32>, Vec<u32>) =
         (Vec::new(), Vec::new(), Vec::new(), Vec::new());
-    let mut bytes_win: u64 = 0;
     let mut last_dropped_batches: u64 = 0;
     // Absolute next-frame deadline — the single pacing clock for the loop.
     let mut next_frame = Instant::now();
@@ -580,6 +665,22 @@ fn stream_body(
     const MAX_REBUILDS: u32 = 5;
     let mut rebuilds: u32 = 0;
 
+    // Coalesce forced keyframes. Under loss Moonlight spams IDR/RFI requests; on an encoder without
+    // RFI (VAAPI/AMD — `supports_rfi=false`) each one becomes a full IDR, so an un-coalesced request
+    // stream turns EVERY frame into a 4K IDR, saturates the send path, and collapses the session
+    // instead of recovering. One fresh IDR already resolves all pending loss, so after emitting one
+    // we ignore further keyframe requests for a short in-flight window (~2 frames). NVENC
+    // ref-invalidation (cheap, no IDR spike) is never rate-limited — only full keyframes are.
+    let keyframe_coalesce = frame_interval * 2;
+    let mut last_keyframe: Option<Instant> = None;
+    // A frame dropped at the pipeline head (below) breaks the reference chain for the following
+    // P-frames: the client never receives it, but the encoder advanced its references past it, and —
+    // packetization being downstream now — a dropped frame consumes no frameIndex for the client to
+    // detect the gap. So the host re-anchors itself: a drop arms a keyframe on the next iteration,
+    // routed through the same coalesce gate as client IDR requests so a burst of drops (congestion)
+    // can't become an IDR storm.
+    let mut recover_after_drop = false;
+
     while running.load(Ordering::SeqCst) {
         let tick = Instant::now();
         // Measure per-stage timing when `PUNKTFUNK_PERF` is set OR a web-console stats capture is
@@ -645,6 +746,7 @@ fn stream_body(
                 .context("reopen encoder after rebuild")?;
                 supports_rfi = enc.caps().supports_rfi;
                 enc.request_keyframe();
+                last_keyframe = Some(Instant::now());
                 next_frame = Instant::now();
                 tracing::info!("gamestream: source rebuilt — stream continues");
                 continue;
@@ -654,58 +756,71 @@ fn stream_body(
         // Honor a client recovery request. Prefer reference-frame invalidation (the encoder
         // re-references an older still-valid frame — no costly IDR spike); if the encoder can't
         // invalidate (range too old, or no NVENC RFI) it returns false and we force a keyframe.
+        // A prior pipeline drop needs a fresh keyframe to re-anchor the reference chain (see below).
+        let mut want_keyframe = recover_after_drop;
+        recover_after_drop = false;
         if let Some((first, last)) = rfi_range.lock().unwrap().take() {
             // Prefer reference-frame invalidation when the encoder supports it (no costly IDR
-            // spike); otherwise — or if the range is too old to invalidate — force a keyframe.
+            // spike); otherwise — or if the range is too old to invalidate — fall back to a keyframe.
             if !(supports_rfi && enc.invalidate_ref_frames(first, last)) {
-                enc.request_keyframe();
+                want_keyframe = true;
             }
         }
-        // An explicit IDR request (or a rangeless RFI) forces a keyframe so the client resyncs
+        // An explicit IDR request (or a rangeless RFI) asks for a keyframe so the client resyncs
         // immediately instead of waiting for the next GOP boundary.
         if force_idr.swap(false, Ordering::SeqCst) {
-            enc.request_keyframe();
+            want_keyframe = true;
+        }
+        // Coalesce: emit at most one forced keyframe per in-flight window, so a burst of recovery
+        // requests during one loss event doesn't turn every frame into a full IDR (see above).
+        if want_keyframe {
+            let now = Instant::now();
+            let emit = match last_keyframe {
+                Some(t) => now.duration_since(t) >= keyframe_coalesce,
+                None => true,
+            };
+            if emit {
+                enc.request_keyframe();
+                last_keyframe = Some(now);
+            } else {
+                tracing::debug!("video: keyframe request coalesced (IDR still in flight)");
+            }
         }
         enc.submit(&frame).context("encoder submit")?;
         let t_enc = tick.elapsed();
 
         // 90 kHz RTP timestamp from wall-clock, so a variable capture rate stays correct.
         let ts = (stream_start.elapsed().as_secs_f64() * 90_000.0) as u32;
-        let mut batch: Vec<Vec<u8>> = Vec::new();
+        // Drain the encoder's access units (owned buffers) — FEC/packetization runs on the
+        // packetizer thread, off this loop, so it never serializes behind encode.
+        let mut aus: Vec<(Vec<u8>, FrameType)> = Vec::new();
         while let Some(au) = enc.poll().context("encoder poll")? {
             let ft = if au.keyframe {
                 FrameType::Idr
             } else {
                 FrameType::P
             };
-            batch.extend(pk.packetize(&au.data, ft, ts));
+            aus.push((au.data, ft));
         }
         let t_pkt = tick.elapsed();
 
-        // Hand the frame's packets to the send thread; never block here. A full queue means
+        // Hand the frame's AUs to the pipeline; never block here. A full queue means the pipeline
-        // the sender is behind — drop this batch (FEC/RFI covers the client) and keep encoding.
+        // (packetizer, or the paced sender behind it) is behind — drop this frame (FEC/RFI covers the
-        let n = batch.len();
+        // client) and keep encoding, so a downstream stall can never cap the encode rate.
-        // Goodput this window = bytes actually queued to the sender (a dropped batch never reaches
+        if !aus.is_empty() {
-        // the wire, so it's excluded). Summed only when measuring, to keep the idle path free.
+            match raw_tx.try_send(RawFrame { aus, ts }) {
-        let batch_bytes: u64 = if measure {
-            batch.iter().map(|p| p.len() as u64).sum()
-        } else {
-            0
-        };
-        if n > 0 {
-            match batch_tx.try_send(batch) {
                 Ok(()) => {
                     sent_batches += 1;
-                    bytes_win += batch_bytes;
                 }
                 Err(std::sync::mpsc::TrySendError::Full(_)) => {
                     dropped_batches += 1;
+                    recover_after_drop = true; // re-anchor the reference chain on the next frame
                     if dropped_batches.is_power_of_two() {
-                        tracing::warn!(dropped_batches, "video: send queue full — frame dropped");
+                        tracing::warn!(dropped_batches, "video: pipeline queue full — frame dropped");
                     }
                 }
                 Err(std::sync::mpsc::TrySendError::Disconnected(_)) => {
-                    break; // sender exited (client gone)
+                    break; // packetizer/sender exited (client gone)
                 }
             }
         }
@@ -713,26 +828,33 @@ fn stream_body(
             let t_send = tick.elapsed();
             let cap_us = t_cap.as_micros();
             let enc_us = (t_enc - t_cap).as_micros();
-            let pkt_us = (t_pkt - t_enc).as_micros();
+            // `poll` = drain the encoder's AUs; `enqueue` = hand-off to the pipeline. FEC/packetize
-            let send_us = (t_send - t_pkt).as_micros();
+            // and the paced send now run on their own threads, off this loop — so both of these
+            // should be small; if they aren't, the encode loop is being stalled by pipeline
+            // backpressure (a full queue), which is the signal that a downstream stage can't keep up.
+            let poll_us = (t_pkt - t_enc).as_micros();
+            let enqueue_us = (t_send - t_pkt).as_micros();
             mx_cap = mx_cap.max(cap_us);
             mx_enc = mx_enc.max(enc_us);
-            mx_pkt = mx_pkt.max(pkt_us);
+            mx_pkt = mx_pkt.max(poll_us);
-            mx_send = mx_send.max(send_us);
+            mx_send = mx_send.max(enqueue_us);
-            mx_pkts = mx_pkts.max(n);
             v_cap.push(cap_us as u32);
             v_enc.push(enc_us as u32);
-            v_pkt.push(pkt_us as u32);
+            v_pkt.push(poll_us as u32);
-            v_send.push(send_us as u32);
+            v_send.push(enqueue_us as u32);
         }
 
         fps_count += 1;
         if fps_t.elapsed() >= Duration::from_secs(1) {
             let secs = fps_t.elapsed().as_secs_f64();
+            // Bytes handed to the wire this window, tallied by the packetizer thread (goodput).
+            let win_bytes = goodput.swap(0, std::sync::atomic::Ordering::Relaxed);
             if perf {
-                // Max µs/stage this second: cap=drain channel, enc=submit (zero-copy device
+                // Max µs/stage this second on the ENCODE loop: cap=drain channel, enc=submit
-                // copy + NVENC), pkt=poll+FEC+packetize, send=paced packet send. `uniq`=new
+                // (zero-copy device copy + NVENC), pkt=poll (AU drain), send=enqueue to the pipeline.
-                // captured frames (vs re-encoded). `pkts`=max packets in one frame (IDR spike).
+                // FEC/packetize and the paced send run on their own threads now, so pkt/send here
+                // should be near-zero — a nonzero value means encode is being stalled by pipeline
+                // backpressure. `uniq`=new captured frames (vs re-encoded).
                 tracing::info!(
                     fps = fps_count,
                     uniq,
@@ -740,7 +862,6 @@ fn stream_body(
                     pkt_us = mx_pkt,
                     send_us = mx_send,
                     cap_us = mx_cap,
-                    max_pkts = mx_pkts,
                     "video: streaming (perf)"
                 );
             } else {
@@ -753,7 +874,7 @@ fn stream_body(
             }
             // Web-console capture: build the aggregated sample. The host send side exposes no
             // receiver-side packet loss / FEC-recovery / send-buffer EAGAIN counters, so those stay
-            // 0 (not fabricated); `frames_dropped` is the per-frame send-queue overflow delta.
+            // 0 (not fabricated); `frames_dropped` is the per-frame pipeline-queue overflow delta.
             if stats.is_armed() {
                 let session_id = *sid.get_or_insert_with(|| {
                     stats.register_session(
@@ -792,7 +913,7 @@ fn stream_body(
                     ],
                     fps: (uniq as f64 / secs) as f32,
                     repeat_fps: (fps_count.saturating_sub(uniq) as f64 / secs) as f32,
-                    mbps: (bytes_win as f64 * 8.0 / secs / 1_000_000.0) as f32,
+                    mbps: (win_bytes as f64 * 8.0 / secs / 1_000_000.0) as f32,
                     bitrate_kbps: cfg.bitrate_kbps,
                     frames_dropped: dropped_batches.saturating_sub(last_dropped_batches) as u32,
                     packets_dropped: 0,
@@ -805,13 +926,11 @@ fn stream_body(
             mx_enc = 0;
             mx_pkt = 0;
             mx_send = 0;
-            mx_pkts = 0;
             uniq = 0;
             v_cap.clear();
             v_enc.clear();
             v_pkt.clear();
             v_send.clear();
-            bytes_win = 0;
             last_dropped_batches = dropped_batches;
             fps_count = 0;
             fps_t = Instant::now();
@@ -889,4 +1008,24 @@ mod tests {
         assert_eq!(got, 3 * PER_FRAME);
         assert!(running.load(Ordering::SeqCst), "no spurious client-gone");
     }
+
+    /// The pacing layout bounds the paced-burst (and thus sleep) count regardless of frame size,
+    /// while always covering every packet and keeping small frames on the 16-packet floor. Guards
+    /// the 4K/high-bitrate "send queue full" regression (a fixed 16-packet chunk fanned a ~600
+    /// packet frame into ~38 sleeps, whose overshoot blew the per-frame send budget).
+    #[test]
+    fn pace_layout_bounds_step_count() {
+        for &n in &[1usize, 16, 146, 610, 1024, 5000, 50_000] {
+            let (chunk, steps) = pace_layout(n);
+            assert!(steps >= 1, "n={n}: at least one step");
+            assert!(steps <= 12, "n={n}: step count {steps} exceeded the cap");
+            assert!(chunk >= 16, "n={n}: chunk {chunk} below the 16-packet floor");
+            assert!(chunk * steps >= n, "n={n}: {chunk}×{steps} must cover all packets");
+        }
+        // Small frames stay on the floor: one 16-packet burst.
+        assert_eq!(pace_layout(1), (16, 1));
+        assert_eq!(pace_layout(16), (16, 1));
+        // A 4K/250Mbps frame (~600 packets) was ~38 bursts at a fixed 16 — now bounded.
+        assert!(pace_layout(610).1 <= 12);
+    }
 }

crates/punktfunk-host/src/main.rs

@@ -418,6 +418,20 @@ fn real_main() -> Result<()> {
                 allow_pairing: true,
                 pairing_pin: None,
                 paired_store: None,
+                // Fixed data-plane port: bind it and stream direct (no hole-punch), removing the
+                // ~2.5 s punch-timeout on a firewalled host. Default (absent) = a random port +
+                // hole-punch. Also honors PUNKTFUNK_DATA_PORT.
+                data_port: get("--data-port")
+                    .map(str::to_string)
+                    .or_else(|| std::env::var("PUNKTFUNK_DATA_PORT").ok())
+                    .and_then(|s| s.parse().ok()),
+                // Disconnect-detection latency (QUIC control-connection idle timeout): --idle-timeout-ms
+                // overrides PUNKTFUNK_IDLE_TIMEOUT_MS; absent = the core default (8s).
+                idle_timeout: get("--idle-timeout-ms")
+                    .and_then(|s| s.trim().parse::<u64>().ok())
+                    .filter(|&ms| ms > 0)
+                    .map(std::time::Duration::from_millis)
+                    .or_else(punktfunk1::idle_timeout_from_env),
             })
         }
         // Windows service control: install/uninstall/start/stop/status + the SCM `run` entry point.
@@ -501,6 +515,12 @@ fn input_test() -> Result<()> {
 fn parse_serve(args: &[String]) -> Result<(mgmt::Options, punktfunk1::NativeServe, bool)> {
     let mut opts = mgmt::Options::default();
     let mut native_port: u16 = 9777; // the native plane always runs now
+    // Fixed data-plane UDP port: `Some(p)` binds p and streams direct (no hole-punch, no ~2.5 s
+    // punch-timeout on a firewalled host); `None` (default) = a random port + hole-punch. Env
+    // default, `--data-port` overrides.
+    let mut data_port: Option<u16> = std::env::var("PUNKTFUNK_DATA_PORT")
+        .ok()
+        .and_then(|s| s.parse().ok());
     let mut open = false;
     let mut gamestream = false;
     // Did the operator pin the mgmt bind themselves? If not, we LAN-expose the read surface below so
@@ -541,6 +561,13 @@ fn parse_serve(args: &[String]) -> Result<(mgmt::Options, punktfunk1::NativeServ
                     .parse()
                     .map_err(|_| anyhow::anyhow!("bad --native-port (want a port number)"))?
             }
+            "--data-port" => {
+                data_port = Some(
+                    next()?
+                        .parse()
+                        .map_err(|_| anyhow::anyhow!("bad --data-port (want a port number)"))?,
+                )
+            }
             // Opt into the GameStream/Moonlight-compat planes (off by default — they carry the
             // inherent on-path #5/#9 weaknesses; only for a trusted LAN).
             "--gamestream" | "--moonlight" => gamestream = true,
@@ -576,6 +603,7 @@ fn parse_serve(args: &[String]) -> Result<(mgmt::Options, punktfunk1::NativeServ
         // Advertise the mgmt port over mDNS so clients learn where to browse the library (rather than
         // assuming the default). `opts.bind.port()` is the real port even if the operator moved it.
         mgmt_port: opts.bind.port(),
+        data_port,
     };
     Ok((opts, native, gamestream))
 }
@@ -703,6 +731,10 @@ SERVE OPTIONS:
                                  reuse, security-review #5/#9); enable only on a TRUSTED LAN
     --native                     no-op (the native punktfunk/1 plane always runs in `serve` now)
     --native-port <PORT>         native QUIC port (default 9777)
+    --data-port <PORT>           pin the per-session video data plane to this fixed UDP port and
+                                 stream direct (no hole-punch) — open exactly this port in a host
+                                 firewall to avoid the ~2.5 s punch-timeout. Default (unset) or
+                                 PUNKTFUNK_DATA_PORT: a random port + hole-punch (crosses NAT)
     --open                       disable mandatory native pairing (default: pairing REQUIRED —
                                  an open host any LAN device can stream from is insecure)
 
@@ -714,6 +746,10 @@ PUNKTFUNK1-HOST OPTIONS:
     --max-sessions <N>           exit after N sessions; 0 = serve forever (default: 0)
     --max-concurrent <N>         stream at most N sessions at once (NVENC bound); overflow waits
                                  in the accept queue; 0 = unlimited (default: 4)
+    --data-port <PORT>           pin the video data plane to this fixed UDP port and stream direct
+                                 (no hole-punch; open exactly this port to skip the ~2.5 s punch-
+                                 timeout). Default or PUNKTFUNK_DATA_PORT: random port + hole-punch.
+                                 A fixed port fits one session; concurrent ones fall back to random
     --allow-tofu                 also accept UNPAIRED clients (trust-on-first-use) and advertise
                                  pair=optional. Default: pairing REQUIRED — the host rejects
                                  unpaired clients and logs a 4-digit pairing PIN at startup;

crates/punktfunk-host/src/mgmt.rs

@@ -156,6 +156,11 @@ fn api_router_parts() -> (Router<Arc<MgmtState>>, utoipa::openapi::OpenApi) {
                 .routes(routes!(list_compositors))
                 .routes(routes!(list_gpus))
                 .routes(routes!(set_gpu_preference))
+                .routes(routes!(get_display_settings))
+                .routes(routes!(set_display_settings))
+                .routes(routes!(get_display_state))
+                .routes(routes!(release_display))
+                .routes(routes!(set_display_layout))
                 .routes(routes!(get_status))
                 .routes(routes!(get_local_summary))
                 .routes(routes!(list_paired_clients))
@@ -210,6 +215,7 @@ pub fn openapi_json() -> String {
     tags(
         (name = "host", description = "Host identity, capabilities, and liveness"),
         (name = "gpu", description = "GPU inventory and selection: list the host's GPUs, choose automatic or a preferred GPU, see the one in use"),
+        (name = "display", description = "Virtual-display management policy: lifecycle (keep-alive), topology (primary/exclusive), conflict handling, identity, and layout"),
         (name = "clients", description = "Paired Moonlight client management"),
         (name = "pairing", description = "Pairing PIN delivery (the out-of-band half of the GameStream pairing handshake)"),
         (name = "native", description = "Native punktfunk/1 pairing: arm a window, display the host PIN, manage paired devices"),
@@ -376,6 +382,10 @@ struct LocalSummary {
     pin_pending: bool,
     /// Native pairing knocks awaiting the operator's approval (count only).
     pending_approvals: u32,
+    /// Virtual displays being KEPT with no live session — lingering (keep-alive window) or pinned
+    /// (`keep_alive: forever`). Non-zero means a display (and, exclusive, your physical monitors) is
+    /// held; the tray surfaces it + a one-click release. Active (in-use) displays are not counted.
+    kept_displays: u32,
 }
 
 /// A paired (certificate-pinned) Moonlight client.
@@ -954,6 +964,304 @@ async fn set_gpu_preference(ApiJson(req): ApiJson<SetGpuPreference>) -> Response
     Json(gpu_state()).into_response()
 }
 
+// ---------------------------------------------------------------------------------------
+// Display management (design/display-management.md)
+// ---------------------------------------------------------------------------------------
+
+/// One preset's human-facing description + the fields it expands to, so the console can render a
+/// preset picker with an accurate "what this does" preview without hardcoding the expansion.
+#[derive(Serialize, ToSchema)]
+struct PresetInfo {
+    /// The preset id (`default` | `gaming-rig` | `shared-desktop` | `hotdesk` | `workstation`).
+    id: String,
+    /// One-line story shown next to the option.
+    summary: String,
+    /// The effective policy this preset expands to (the same fields a `custom` policy carries).
+    fields: crate::vdisplay::policy::EffectivePolicy,
+}
+
+/// Full display-management state for the console: the stored policy, every preset's expansion, the
+/// resolved effective policy, and which options this build actually enforces yet (Stage 0 wires
+/// keep-alive linger + topology; the rest are stored but not yet acted on).
+#[derive(Serialize, ToSchema)]
+struct DisplaySettingsState {
+    /// The stored policy (preset + custom fields), or the built-in default when unconfigured.
+    settings: crate::vdisplay::policy::DisplayPolicy,
+    /// True once a `display-settings.json` exists (the console has configured this host).
+    configured: bool,
+    /// The effective (preset-expanded) policy currently in force.
+    effective: crate::vdisplay::policy::EffectivePolicy,
+    /// Every named preset and what it expands to (for the picker's preview).
+    presets: Vec<PresetInfo>,
+    /// Option names this build enforces right now. All five axes are now acted on (keep_alive +
+    /// topology since Stage 0-2, identity Stage 3, mode_conflict Stage 4, layout Stage 5) — the console
+    /// reads this to know which controls are live vs. "coming soon" (per-backend nuance, e.g. layout
+    /// position apply being KWin-only, is reported per display in `/display/state`).
+    enforced: Vec<String>,
+}
+
+fn preset_summary(id: &str) -> &'static str {
+    match id {
+        "default" => "Today's behavior: a short linger absorbs reconnects, the streamed output is the sole desktop, extra clients get their own view.",
+        "gaming-rig" => "Dedicated couch/headless box: the game and its display survive disconnects; whoever connects takes the box over.",
+        "shared-desktop" => "A desktop you also use in person: never blank the real monitors, never keep ghost displays, concurrent viewers each get a view.",
+        "hotdesk" => "One user at a time with fast reattach; a second user is told the box is busy; each device+resolution keeps its own scaling.",
+        "workstation" => "Multi-monitor daily driver: your displays come back exactly where you arranged them, per-client identity, exclusive.",
+        _ => "",
+    }
+}
+
+fn display_settings_state() -> DisplaySettingsState {
+    use crate::vdisplay::policy::{self, Preset};
+    let store = policy::prefs();
+    let settings = store.get();
+    let configured = store.configured().is_some();
+    let presets = [
+        ("default", Preset::Default),
+        ("gaming-rig", Preset::GamingRig),
+        ("shared-desktop", Preset::SharedDesktop),
+        ("hotdesk", Preset::Hotdesk),
+        ("workstation", Preset::Workstation),
+    ]
+    .into_iter()
+    .filter_map(|(id, p)| {
+        policy::preset_fields(p).map(|e| PresetInfo {
+            id: id.to_string(),
+            summary: preset_summary(id).to_string(),
+            fields: e,
+        })
+    })
+    .collect();
+    DisplaySettingsState {
+        effective: settings.effective(),
+        settings,
+        configured,
+        presets,
+        enforced: vec![
+            "keep_alive".into(),
+            "topology".into(),
+            "mode_conflict".into(),
+            "identity".into(),
+            "layout".into(),
+        ],
+    }
+}
+
+/// Display-management policy
+///
+/// The stored virtual-display policy (lifecycle, topology, conflict handling, identity, layout),
+/// every preset's expansion, and which options this build enforces yet. See
+/// `design/display-management.md`.
+#[utoipa::path(
+    get,
+    path = "/display/settings",
+    tag = "display",
+    operation_id = "getDisplaySettings",
+    responses(
+        (status = OK, description = "Stored policy + preset expansions + enforced options", body = DisplaySettingsState),
+        (status = UNAUTHORIZED, description = "Missing or invalid bearer token", body = ApiError),
+    )
+)]
+async fn get_display_settings() -> Json<DisplaySettingsState> {
+    Json(display_settings_state())
+}
+
+/// Set the display-management policy
+///
+/// Persists a new policy (validated + clamped) and applies it from the next connect/teardown — a
+/// running session keeps the display it opened on. `keep_alive: forever` (the gaming-rig preset) is
+/// honored (the display is Pinned; free it via `POST /display/release`).
+#[utoipa::path(
+    put,
+    path = "/display/settings",
+    tag = "display",
+    operation_id = "setDisplaySettings",
+    request_body = crate::vdisplay::policy::DisplayPolicy,
+    responses(
+        (status = OK, description = "Policy stored; the new state", body = DisplaySettingsState),
+        (status = BAD_REQUEST, description = "Malformed policy body", body = ApiError),
+        (status = INTERNAL_SERVER_ERROR, description = "Policy could not be persisted", body = ApiError),
+        (status = UNAUTHORIZED, description = "Missing or invalid bearer token", body = ApiError),
+    )
+)]
+async fn set_display_settings(
+    ApiJson(policy): ApiJson<crate::vdisplay::policy::DisplayPolicy>,
+) -> Response {
+    // `keep_alive: forever` (the gaming-rig preset) is now honored: the display is Pinned (Linux
+    // registry + Windows `MgrState::Pinned`) and freed via `POST /display/release` (the escape hatch).
+    if let Err(e) = crate::vdisplay::policy::prefs().set(policy) {
+        return api_error(
+            StatusCode::INTERNAL_SERVER_ERROR,
+            &format!("persist display policy: {e:#}"),
+        );
+    }
+    tracing::info!("management API: display policy updated");
+    Json(display_settings_state()).into_response()
+}
+
+/// One live or kept virtual display.
+#[derive(Serialize, ToSchema)]
+struct ApiDisplayInfo {
+    /// Stable-enough id for the `/display/release` `slot` argument.
+    slot: u64,
+    /// Backend name (`pf-vdisplay`, `kwin`, …).
+    backend: String,
+    /// `WIDTHxHEIGHT@HZ`.
+    mode: String,
+    /// `active` | `lingering` | `pinned`.
+    state: String,
+    /// Milliseconds until a lingering display is torn down (absent when active/pinned).
+    expires_in_ms: Option<u64>,
+    /// Live sessions holding the display.
+    sessions: u32,
+    /// Short client label, when the owner tracks it.
+    client: Option<String>,
+    /// Display group (shared desktop) id — several displays with the same group form one desktop (§6A).
+    group: u32,
+    /// This display's ordinal within its group, in acquire order (0-based).
+    display_index: u32,
+    /// Desktop-space top-left `x` (auto-row or the console's manual arrangement, §6.2).
+    x: i32,
+    /// Desktop-space top-left `y`.
+    y: i32,
+    /// Stable per-client identity slot keying persistent config + manual layout (absent = shared/anonymous).
+    identity_slot: Option<u32>,
+    /// Effective topology for this display's group (`extend` | `primary` | `exclusive`).
+    topology: String,
+}
+
+/// The host's managed virtual displays right now.
+#[derive(Serialize, ToSchema)]
+struct DisplayStateResponse {
+    displays: Vec<ApiDisplayInfo>,
+}
+
+/// Request body for `releaseDisplay`.
+#[derive(Deserialize, ToSchema)]
+struct ReleaseDisplayRequest {
+    /// Slot to release (see `state`); omit to release **all** kept displays.
+    #[serde(default)]
+    slot: Option<u64>,
+}
+
+/// Result of a `/display/release`.
+#[derive(Serialize, ToSchema)]
+struct ReleaseDisplayResult {
+    /// Number of kept displays torn down.
+    released: usize,
+}
+
+/// Live virtual displays
+///
+/// The host's managed virtual displays right now — active (streaming), lingering (kept after
+/// disconnect, counting down to teardown), or pinned (kept indefinitely). See
+/// `design/display-management.md`.
+#[utoipa::path(
+    get,
+    path = "/display/state",
+    tag = "display",
+    operation_id = "getDisplayState",
+    responses(
+        (status = OK, description = "The live/kept virtual displays", body = DisplayStateResponse),
+        (status = UNAUTHORIZED, description = "Missing or invalid bearer token", body = ApiError),
+    )
+)]
+async fn get_display_state() -> Json<DisplayStateResponse> {
+    let snap = crate::vdisplay::registry::snapshot();
+    Json(DisplayStateResponse {
+        displays: snap
+            .displays
+            .into_iter()
+            .map(|d| ApiDisplayInfo {
+                slot: d.slot,
+                backend: d.backend,
+                mode: format!("{}x{}@{}", d.mode.0, d.mode.1, d.mode.2),
+                state: d.state,
+                expires_in_ms: d.expires_in_ms,
+                sessions: d.sessions,
+                client: d.client,
+                group: d.group,
+                display_index: d.display_index,
+                x: d.position.0,
+                y: d.position.1,
+                identity_slot: d.identity_slot,
+                topology: d.topology,
+            })
+            .collect(),
+    })
+}
+
+/// Release kept virtual displays
+///
+/// Tear down lingering/pinned displays now — so a physical-screen user gets their screen back
+/// without waiting out the linger. `slot` releases one; omit it to release all kept displays.
+/// Active (streaming) displays are never torn down here (that is session control).
+#[utoipa::path(
+    post,
+    path = "/display/release",
+    tag = "display",
+    operation_id = "releaseDisplay",
+    request_body = ReleaseDisplayRequest,
+    responses(
+        (status = OK, description = "The number of kept displays released", body = ReleaseDisplayResult),
+        (status = UNAUTHORIZED, description = "Missing or invalid bearer token", body = ApiError),
+    )
+)]
+async fn release_display(
+    ApiJson(req): ApiJson<ReleaseDisplayRequest>,
+) -> Json<ReleaseDisplayResult> {
+    let released = crate::vdisplay::registry::release(req.slot);
+    tracing::info!(slot = ?req.slot, released, "management API: display release");
+    Json(ReleaseDisplayResult { released })
+}
+
+/// Request body for `setDisplayLayout`: per-identity-slot desktop offsets, keyed by the identity-slot
+/// id as a string (the same id `/display/state` reports as `identity_slot`).
+#[derive(Deserialize, ToSchema)]
+struct DisplayLayoutRequest {
+    /// `{"<identity_slot>": {"x": …, "y": …}}` — where each arranged display's top-left sits.
+    #[serde(default)]
+    positions: std::collections::BTreeMap<String, crate::vdisplay::policy::Position>,
+}
+
+/// Arrange virtual displays
+///
+/// Set the **manual** desktop arrangement — per-identity-slot `(x, y)` offsets so a multi-monitor
+/// group (§6A/§6B) comes back where the operator placed it. Persisted into the policy's layout block
+/// and switched to manual mode; applied from the next connect (a live group re-applies on its next
+/// acquire). Locks in the current effective behavior as explicit fields, so arranging displays never
+/// silently changes keep-alive/topology/conflict/identity. See `design/display-management.md` §6.2.
+#[utoipa::path(
+    put,
+    path = "/display/layout",
+    tag = "display",
+    operation_id = "setDisplayLayout",
+    request_body = DisplayLayoutRequest,
+    responses(
+        (status = OK, description = "Layout stored; the new settings state", body = DisplaySettingsState),
+        (status = INTERNAL_SERVER_ERROR, description = "Layout could not be persisted", body = ApiError),
+        (status = UNAUTHORIZED, description = "Missing or invalid bearer token", body = ApiError),
+    )
+)]
+async fn set_display_layout(ApiJson(req): ApiJson<DisplayLayoutRequest>) -> Response {
+    let store = crate::vdisplay::policy::prefs();
+    // Lock the current effective behavior into explicit fields + set the manual arrangement (pure
+    // transform, unit-tested in `policy.rs`) — so arranging displays is orthogonal to the other policy
+    // axes. (`effective` keep_alive is never `Forever` via the API — the settings PUT rejects it.)
+    let policy = store.get().effective().with_manual_layout(req.positions);
+    if let Err(e) = store.set(policy) {
+        return api_error(
+            StatusCode::INTERNAL_SERVER_ERROR,
+            &format!("persist display layout: {e:#}"),
+        );
+    }
+    tracing::info!(
+        positions = display_settings_state().settings.layout.positions.len(),
+        "management API: display layout updated"
+    );
+    Json(display_settings_state()).into_response()
+}
+
 /// Live host status
 #[utoipa::path(
     get,
@@ -1026,6 +1334,11 @@ async fn get_local_summary(State(st): State<Arc<MgmtState>>) -> Json<LocalSummar
         native_paired_clients,
         pin_pending: st.app.pairing.pin.awaiting_pin(),
         pending_approvals,
+        kept_displays: crate::vdisplay::registry::snapshot()
+            .displays
+            .iter()
+            .filter(|d| d.state == "lingering" || d.state == "pinned")
+            .count() as u32,
     })
 }
 
@@ -2257,6 +2570,7 @@ mod tests {
             fps: 120,
             appid: 1,
             peer_ip: None,
+            owner_fp: None,
         });
         state.streaming.store(true, Ordering::SeqCst);
 
@@ -2383,6 +2697,7 @@ mod tests {
             fps: 60,
             appid: 1,
             peer_ip: None,
+            owner_fp: None,
         });
 
         let del = axum::http::Request::delete("/api/v1/session")
@@ -2473,6 +2788,74 @@ mod tests {
             .unwrap()
     }
 
+    /// The display-management GET surface (presets + effective + the enforced-axes list). READ-ONLY
+    /// on purpose: `prefs()` is a process-global `OnceLock`, so a PUT here would clobber it and race
+    /// other tests running in the same process. `keep_alive: forever` (gaming-rig) is now accepted
+    /// (not rejected) — that acceptance is covered on-glass (`.116`) + by the pure `policy` tests, and
+    /// the `forever` value is read off the surfaced preset below without writing.
+    #[tokio::test]
+    async fn display_settings_surface() {
+        let app = test_app(test_state(), None);
+
+        let (status, body) = send(&app, get_req("/api/v1/display/settings")).await;
+        assert_eq!(status, StatusCode::OK);
+        let presets = body["presets"].as_array().expect("presets array");
+        assert_eq!(
+            presets.len(),
+            5,
+            "all five named presets are surfaced for the console picker"
+        );
+        assert!(
+            body["effective"]["keep_alive"].is_object(),
+            "the effective policy is echoed"
+        );
+        // gaming-rig surfaces keep_alive: forever (no longer rejected) — read it off the preset list.
+        let gaming = presets
+            .iter()
+            .find(|p| p["id"] == "gaming-rig")
+            .expect("gaming-rig preset surfaced");
+        assert_eq!(
+            gaming["fields"]["keep_alive"]["mode"], "forever",
+            "gaming-rig is keep_alive: forever"
+        );
+        let enforced: Vec<&str> = body["enforced"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .filter_map(|v| v.as_str())
+            .collect();
+        // All five axes are enforced now (Stages 0-5).
+        assert!(enforced.contains(&"keep_alive"));
+        assert!(enforced.contains(&"topology"));
+        assert!(enforced.contains(&"mode_conflict"));
+        assert!(enforced.contains(&"identity"));
+        assert!(enforced.contains(&"layout"));
+    }
+
+    /// The display state/release endpoints are wired + auth-gated. On the test host no backend has
+    /// created a display (and non-Windows reports none), so `/state` is empty and `/release` is a
+    /// no-op — the shapes + the "nothing to release" path, without touching any global owner.
+    #[tokio::test]
+    async fn display_state_and_release_empty() {
+        let app = test_app(test_state(), None);
+
+        let (status, body) = send(&app, get_req("/api/v1/display/state")).await;
+        assert_eq!(status, StatusCode::OK);
+        assert_eq!(
+            body["displays"].as_array().map(|a| a.len()),
+            Some(0),
+            "no managed displays on an idle test host"
+        );
+
+        let (status, body) = send(
+            &app,
+            post_json("/api/v1/display/release", serde_json::json!({})),
+        )
+        .await;
+        assert_eq!(status, StatusCode::OK);
+        assert_eq!(body["released"], 0);
+    }
+
     #[tokio::test]
     async fn native_pairing_arm_show_and_unpair() {
         let np = Arc::new(

crates/punktfunk-host/src/punktfunk1.rs

@@ -75,6 +75,41 @@ pub struct Punktfunk1Options {
     pub pairing_pin: Option<String>,
     /// Paired-clients store path override (tests); `None` = the default config path.
     pub paired_store: Option<std::path::PathBuf>,
+    /// Fixed data-plane UDP port. `None`/`Some(0)` (default): bind a random ephemeral port and
+    /// **hole-punch** — wait ~2.5 s for the client's punch, then fall back to its reported address
+    /// (traverses NAT / a stateful inter-VLAN firewall with no forwarded port, at the cost of the
+    /// punch-timeout on a firewall that drops the punch). `Some(p)`: bind that fixed port and
+    /// stream **directly** to the client's reported address with no punch-wait — for a host whose
+    /// data port is fixed + firewall-opened/forwarded, this removes the punch-timeout delay. A
+    /// fixed port only fits one data plane at a time, so a concurrent session finding it busy
+    /// falls back to random + hole-punch (see [`bind_data_socket`]).
+    pub data_port: Option<u16>,
+    /// Control-connection idle timeout — the **disconnect-detection latency** (how long a vanished
+    /// client takes to be declared dead, which bounds how fast a dropped session tears down / lingers
+    /// and thus the reconnect-overlap window). `None` = the core default (8s). Set from
+    /// `PUNKTFUNK_IDLE_TIMEOUT_MS`; clamped to a ≥1s floor with a keep-alive that scales to it so a
+    /// live session never false-closes.
+    pub idle_timeout: Option<std::time::Duration>,
+}
+
+/// Bind the per-session data-plane UDP socket, honoring [`Punktfunk1Options::data_port`]. Returns
+/// `(socket, direct)`: `direct = true` (a successfully-bound fixed port) means "stream straight to
+/// the client's reported address, no hole-punch"; `false` (random port, or a busy fixed port) means
+/// "hole-punch". The socket is held from the handshake through streaming — no drop-then-rebind
+/// window in which a concurrent session could steal a fixed port.
+fn bind_data_socket(data_port: Option<u16>) -> std::io::Result<(std::net::UdpSocket, bool)> {
+    if let Some(p) = data_port.filter(|p| *p != 0) {
+        match std::net::UdpSocket::bind(("0.0.0.0", p)) {
+            Ok(sock) => return Ok((sock, true)),
+            Err(e) => tracing::warn!(
+                data_port = p,
+                error = %e,
+                "fixed --data-port is busy (a concurrent session already holds it?) — \
+                 falling back to a random port + hole-punch for this session"
+            ),
+        }
+    }
+    Ok((std::net::UdpSocket::bind("0.0.0.0:0")?, false))
 }
 
 /// The native (punktfunk/1) trust store + on-demand arming PIN, shared with the management API.
@@ -143,6 +178,9 @@ pub(crate) struct NativeServe {
     /// The management API's TCP port, advertised over mDNS so a client browses the game library on
     /// the same host IP (the unified `serve` always runs the mgmt API, so this is its bind port).
     pub mgmt_port: u16,
+    /// Fixed data-plane UDP port (`--data-port` / `PUNKTFUNK_DATA_PORT`); see
+    /// [`Punktfunk1Options::data_port`]. `None` = random port + hole-punch (the default).
+    pub data_port: Option<u16>,
 }
 
 /// Options for the native host when the unified `serve --native` runs it: real virtual capture,
@@ -153,6 +191,17 @@ pub(crate) struct NativeServe {
 /// overflow clients wait in the accept queue. Override with `--max-concurrent`.
 pub(crate) const DEFAULT_MAX_CONCURRENT: usize = 4;
 
+/// The control-connection idle timeout (disconnect-detection latency) from
+/// `PUNKTFUNK_IDLE_TIMEOUT_MS`; `None` (unset/invalid/zero) = the core default (8s). Clamped
+/// downstream to a ≥1s floor with a keep-alive that scales to it, so a live session never false-closes.
+pub(crate) fn idle_timeout_from_env() -> Option<std::time::Duration> {
+    std::env::var("PUNKTFUNK_IDLE_TIMEOUT_MS")
+        .ok()
+        .and_then(|s| s.trim().parse::<u64>().ok())
+        .filter(|&ms| ms > 0)
+        .map(std::time::Duration::from_millis)
+}
+
 pub(crate) fn native_serve_opts(cfg: &NativeServe) -> Punktfunk1Options {
     Punktfunk1Options {
         port: cfg.port,
@@ -165,6 +214,8 @@ pub(crate) fn native_serve_opts(cfg: &NativeServe) -> Punktfunk1Options {
         allow_pairing: false,
         pairing_pin: None,
         paired_store: None,
+        data_port: cfg.data_port,
+        idle_timeout: idle_timeout_from_env(),
     }
 }
 
@@ -178,10 +229,11 @@ pub(crate) async fn serve(
         .context("load host identity (~/.config/punktfunk)")?;
     let fingerprint = endpoint::fingerprint_of_pem(&identity.cert_pem)
         .map_err(|e| anyhow!("cert fingerprint: {e}"))?;
-    let ep = endpoint::server_with_identity(
+    let ep = endpoint::server_with_identity_idle(
         ([0, 0, 0, 0], opts.port).into(),
         &identity.cert_pem,
         &identity.key_pem,
+        opts.idle_timeout.unwrap_or(endpoint::DEFAULT_IDLE_TIMEOUT),
     )
     .map_err(|e| anyhow!("QUIC server endpoint: {e}"))?;
     tracing::info!(
@@ -341,6 +393,18 @@ pub(crate) async fn serve(
 /// connects and never finishes the handshake would otherwise wedge the host for everyone.
 const HANDSHAKE_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(10);
 
+/// QUIC application error code the host closes with on a `mode_conflict = reject` admission refusal,
+/// carrying the human-readable busy reason (live mode + client label) the client surfaces. A distinct
+/// code lets a client tell "host busy" apart from a transport failure.
+const REJECT_BUSY_CODE: u32 = 0x42;
+
+/// QUIC application error code a client closes with on a **deliberate quit** (a user "stop", not a
+/// network drop). The host reads it off the connection's `ApplicationClosed` reason and tears the
+/// session's virtual display down IMMEDIATELY, skipping the keep-alive linger — an unwanted disconnect
+/// (idle timeout / reset / any other code) still lingers so a reconnect can resume. Shared with the
+/// clients via `punktfunk_core::quic::QUIT_CLOSE_CODE`.
+const QUIT_CODE: u32 = punktfunk_core::quic::QUIT_CLOSE_CODE;
+
 /// Encoder bitrate (kbps) the host falls back to when the client expresses no preference
 /// (`Hello::bitrate_kbps == 0`) — the long-standing 20 Mbps default. A client that knows its
 /// link (e.g. after a speed test) requests an explicit rate instead.
@@ -651,8 +715,9 @@ async fn serve_session(
 
     let source = opts.source;
     let frames = opts.frames;
+    let data_port = opts.data_port;
     let handshake = async {
-        let hello = Hello::decode(&first).map_err(|e| anyhow!("Hello decode: {e:?}"))?;
+        let mut hello = Hello::decode(&first).map_err(|e| anyhow!("Hello decode: {e:?}"))?;
         anyhow::ensure!(
             hello.abi_version == punktfunk_core::WIRE_VERSION,
             "wire version mismatch: client {} host {}",
@@ -684,6 +749,74 @@ async fn serve_session(
             "video codec negotiated"
         );
 
+        // Mode-conflict ADMISSION (Stage 4): a DIFFERENT client connecting while another client's
+        // session is live is resolved by the `mode_conflict` policy BEFORE the Welcome — `separate`
+        // (default, no change), `join` (serve at the live mode — an honest downgrade the client
+        // renders from the Welcome), `steal` (preempt the victim), or `reject` (refuse the handshake).
+        // A same-client reconnect never conflicts. THIS session registers in the live set once its
+        // data plane is up (below the handshake), so a later client can see + steal it.
+        {
+            use crate::vdisplay::admission::{admit, preempt_same_identity, Admission};
+            let peer_fp = endpoint::peer_fingerprint(&conn);
+
+            // Same-client RECONNECT preempt (design §5.3 "preempts downstream"): if THIS client
+            // already has a live session, it's the zombie of an unwanted disconnect whose QUIC idle
+            // timer hasn't fired yet (detection lags a drop by up to `max_idle_timeout`). Signal it to
+            // stop and give it the release grace so it tears its display down — which, keep-alive on,
+            // lingers — and THIS reconnect REUSES that kept display below instead of landing on a
+            // fresh SECOND one. Independent of the mode_conflict arm (it's our OWN prior session, not
+            // a conflict with a different client), and it runs before we register ourselves so we
+            // never signal our own stop flag.
+            let own_zombies = preempt_same_identity(peer_fp);
+            if !own_zombies.is_empty() {
+                tracing::info!(
+                    count = own_zombies.len(),
+                    "reconnect: preempting this client's own zombie session(s) so the kept display is reused"
+                );
+                for z in &own_zombies {
+                    z.store(true, Ordering::SeqCst);
+                }
+                // Same blind release grace the steal path uses — lets the zombie's loops notice the
+                // stop flag and drop its display (→ Lingering) before we acquire below.
+                tokio::time::sleep(std::time::Duration::from_millis(1500)).await;
+            }
+
+            match admit(peer_fp) {
+                Admission::Separate => {}
+                Admission::Join(m) => {
+                    tracing::info!(
+                        requested =
+                            %format_args!("{}x{}@{}", hello.mode.width, hello.mode.height, hello.mode.refresh_hz),
+                        live = %format_args!("{}x{}@{}", m.0, m.1, m.2),
+                        "mode-conflict: JOIN — admitting at the live display's mode"
+                    );
+                    hello.mode.width = m.0;
+                    hello.mode.height = m.1;
+                    hello.mode.refresh_hz = m.2;
+                }
+                Admission::Steal(victims) => {
+                    tracing::info!(
+                        victims = victims.len(),
+                        "mode-conflict: STEAL — preempting the live session(s)"
+                    );
+                    for v in &victims {
+                        v.store(true, Ordering::SeqCst);
+                    }
+                    // Give the victims the release grace to tear their display down before we acquire.
+                    tokio::time::sleep(std::time::Duration::from_millis(1500)).await;
+                }
+                Admission::Reject(reason) => {
+                    tracing::warn!("mode-conflict: REJECT — {reason}");
+                    // Deliver the reason to the client as a TYPED refusal: close the QUIC connection
+                    // with the BUSY application code + the reason bytes, which the client reads from
+                    // the `ApplicationClosed` error (so its UI can say "host is streaming X to <name>")
+                    // instead of seeing a bare connection drop. Then end the handshake.
+                    conn.close(REJECT_BUSY_CODE.into(), reason.as_bytes());
+                    anyhow::bail!("{reason}");
+                }
+            }
+        }
+
         crate::encode::validate_dimensions(codec, hello.mode.width, hello.mode.height)
             .context("client-requested mode")?;
 
@@ -797,10 +930,12 @@ async fn serve_session(
             "encode chroma"
         );
 
-        // Reserve a UDP port for the data plane (bind, read it back, rebind in UdpTransport).
+        // Reserve the data-plane UDP socket up front and HOLD it through streaming (no
-        let probe = std::net::UdpSocket::bind("0.0.0.0:0")?;
+        // bind→read→drop→rebind window a concurrent session could race for a fixed port). A fixed
-        let udp_port = probe.local_addr()?.port();
+        // `--data-port` yields `direct = true` (stream straight to the client's reported address,
-        drop(probe);
+        // no punch-wait); otherwise a random ephemeral port + hole-punch.
+        let (data_sock, direct) = bind_data_socket(data_port)?;
+        let udp_port = data_sock.local_addr()?.port();
 
         let mut key = [0u8; 16];
         rand::thread_rng().fill_bytes(&mut key);
@@ -860,9 +995,9 @@ async fn serve_session(
 
         let start = Start::decode(&io::read_msg(&mut recv).await?)
             .map_err(|e| anyhow!("Start decode: {e:?}"))?;
-        Ok::<_, anyhow::Error>((hello, welcome, udp_port, start, compositor))
+        Ok::<_, anyhow::Error>((hello, welcome, udp_port, data_sock, direct, start, compositor))
     };
-    let (hello, welcome, udp_port, start, compositor) =
+    let (hello, welcome, udp_port, data_sock, direct, start, compositor) =
         tokio::time::timeout(HANDSHAKE_TIMEOUT, handshake)
             .await
             .map_err(|_| anyhow!("handshake timed out after {HANDSHAKE_TIMEOUT:?}"))??;
@@ -1046,15 +1181,41 @@ async fn serve_session(
 
     // Stop signal: stream duration elapsed or the client went away.
     let stop = Arc::new(AtomicBool::new(false));
+    // Deliberate-quit signal: set (before `stop`, so the display lease reads it on teardown) when the
+    // client closed the connection with `QUIT_CODE` — a user "stop", which skips the keep-alive linger.
+    // A bare disconnect / idle timeout leaves it false → the display lingers for a reconnect.
+    let quit = Arc::new(AtomicBool::new(false));
     {
         let stop = stop.clone();
+        let quit = quit.clone();
         let conn = conn.clone();
         tokio::spawn(async move {
-            conn.closed().await;
+            let reason = conn.closed().await;
+            if matches!(&reason, quinn::ConnectionError::ApplicationClosed(ac)
+                if ac.error_code == quinn::VarInt::from_u32(QUIT_CODE))
+            {
+                quit.store(true, Ordering::SeqCst);
+            }
             stop.store(true, Ordering::SeqCst);
         });
     }
 
+    // Register this now-live session for mode-conflict admission (Stage 4): carry its identity, the
+    // negotiated mode, and its stop flag so a LATER connecting client's admission can see it and
+    // (under `steal`) signal it. The guard removes the entry when this session ends.
+    let _live_guard = {
+        let id = endpoint::peer_fingerprint(&conn);
+        let label = id
+            .map(|fp| fp.iter().take(4).map(|b| format!("{b:02x}")).collect::<String>())
+            .unwrap_or_else(|| "client".to_string());
+        crate::vdisplay::admission::register(
+            id,
+            (welcome.mode.width, welcome.mode.height, welcome.mode.refresh_hz),
+            stop.clone(),
+            label,
+        )
+    };
+
     // Audio plane (virtual source only — synthetic runs are protocol tests): desktop Opus
     // → host→client QUIC datagrams, on its own native thread. Best-effort on every failure
     // (no PipeWire audio, spawn error): the session continues without audio — and a spawn
@@ -1153,6 +1314,7 @@ async fn serve_session(
         crate::encode::ChromaFormat::Yuv420
     };
     let stop_stream = stop.clone();
+    let quit_stream = quit.clone();
     let fec_target_dp = fec_target.clone(); // data-plane handle to the adaptive-FEC target
     let conn_stream = conn.clone(); // for sending the source's real HDR metadata (0xCE) mid-stream
                                     // Per-AU host-timing emission (0xCF): only when the client advertised the cap bit. All
@@ -1168,29 +1330,41 @@ async fn serve_session(
         .unwrap_or_else(|| conn.remote_address().ip().to_string());
     let result: Result<()> = async {
         tokio::task::spawn_blocking(move || -> Result<()> {
-            // Wait briefly for the client to hole-punch our data port, then stream to its OBSERVED
+            // Bring up the (already-bound) data-plane socket. Default: hole-punch — wait briefly
-            // source — so video traverses a NAT / stateful inter-VLAN firewall (the client and host
+            // for the client's punch, then stream to its OBSERVED source, so video traverses a
-            // can be on different subnets; control + side planes ride the client-initiated QUIC, but
+            // NAT / stateful inter-VLAN firewall (control + side planes ride the client-initiated
-            // the raw video UDP needs the client to open the path first). Falls back to the
+            // QUIC, but the raw video UDP needs the client to open the path first); falls back to
-            // client-reported address for clients that don't punch (flat-LAN, unchanged).
+            // the reported address for clients that don't punch (flat-LAN, unchanged). With a fixed
-            let (transport, punched) = match UdpTransport::connect_via_punch(
+            // `--data-port` (`direct`), skip the punch-wait and stream straight to the reported
-                &format!("0.0.0.0:{udp_port}"),
+            // address — the operator declared a reachable, firewall-opened port, so there's no
-                &client_udp.to_string(),
+            // punch-timeout to pay. (Direct trusts the reported port: it can't cross a client-side
-                std::time::Duration::from_millis(2500),
+            // NAT that remaps it.)
-            ) {
+            let bound = if direct {
+                UdpTransport::from_socket(data_sock, &client_udp.to_string()).map(|t| (t, false))
+            } else {
+                UdpTransport::from_socket_punch(
+                    data_sock,
+                    &client_udp.to_string(),
+                    std::time::Duration::from_millis(2500),
+                )
+            };
+            let (transport, punched) = match bound {
                 Ok(v) => v,
                 Err(e) => {
                     // Surface the failure here directly: a data-plane bind error would otherwise be
                     // reported only after teardown (and a teardown stall could swallow it entirely).
-                    tracing::error!(error = %e, %client_udp, udp_port, "data-plane socket bind/hole-punch failed");
+                    tracing::error!(error = %e, %client_udp, udp_port, "data-plane socket setup failed");
                     return Err(anyhow::Error::new(e)).context("bind data plane");
                 }
             };
             tracing::info!(
                 %client_udp,
+                udp_port,
+                direct,
                 punched,
-                "data plane bound (punched=true → streaming to the client's observed source; \
+                "data plane bound (direct=true → fixed --data-port, streaming to the reported \
-                 false → no hole-punch seen, using the reported address)"
+                 address with no hole-punch; else punched=true → the client's observed source, \
+                 false → no punch seen, the reported address)"
             );
             let mut session = Session::new(cfg, Box::new(transport))
                 .map_err(|e| anyhow!("host session: {e:?}"))?;
@@ -1212,6 +1386,7 @@ async fn serve_session(
                         mode,
                         seconds,
                         stop: stop_stream,
+                        quit: quit_stream,
                         reconfig: reconfig_rx,
                         keyframe: keyframe_rx,
                         compositor,
@@ -2751,6 +2926,9 @@ struct SessionContext {
     seconds: u32,
     /// Session stop flag (set on disconnect / reconnect-preempt).
     stop: Arc<AtomicBool>,
+    /// Deliberate-quit flag (set when the client closed with `QUIT_CODE`): the display lease reads it
+    /// on teardown to skip the keep-alive linger for a user "stop" (vs. an unwanted disconnect).
+    quit: Arc<AtomicBool>,
     /// Accepted mid-stream mode switches — the pipeline is rebuilt at the new mode.
     reconfig: std::sync::mpsc::Receiver<punktfunk_core::Mode>,
     /// Client decode-recovery keyframe requests.
@@ -2810,6 +2988,7 @@ fn virtual_stream(ctx: SessionContext) -> Result<()> {
         mode,
         seconds,
         stop,
+        quit,
         reconfig,
         keyframe,
         compositor,
@@ -2860,7 +3039,7 @@ fn virtual_stream(ctx: SessionContext) -> Result<()> {
     let _idd_setup_guard = (plan.capture == crate::session_plan::CaptureBackend::IddPush)
         .then(|| crate::vdisplay::manager::vdm().begin_idd_setup(stop.clone()));
     let (mut capturer, mut enc, mut frame, mut interval) =
-        build_pipeline_with_retry(&mut vd, mode, bitrate_kbps, bit_depth, plan)?;
+        build_pipeline_with_retry(&mut vd, mode, bitrate_kbps, bit_depth, plan, &quit)?;
     // Setup done — release the IDD-push setup lock so the next reconnect can begin (and preempt us).
     #[cfg(target_os = "windows")]
     drop(_idd_setup_guard);
@@ -3028,6 +3207,7 @@ fn virtual_stream(ctx: SessionContext) -> Result<()> {
                             bitrate_kbps,
                             bit_depth,
                             plan,
+                            &quit,
                         )?;
                         Ok((new_vd, pipe))
                     })();
@@ -3071,7 +3251,7 @@ fn virtual_stream(ctx: SessionContext) -> Result<()> {
             // Build the new pipeline BEFORE dropping the old one: the host already acked
             // the switch as accepted, so a rebuild failure must not kill an otherwise
             // healthy session — keep streaming the current mode and log instead.
-            match build_pipeline(&mut vd, new_mode, bitrate_kbps, bit_depth, plan) {
+            match build_pipeline(&mut vd, new_mode, bitrate_kbps, bit_depth, plan, &quit) {
                 Ok(next_pipe) => {
                     (capturer, enc, frame, interval) = next_pipe;
                     cur_mode = new_mode;
@@ -3192,6 +3372,7 @@ fn virtual_stream(ctx: SessionContext) -> Result<()> {
                         bitrate_kbps,
                         bit_depth,
                         plan,
+                        &quit,
                     ) {
                         Ok(p) => break p,
                         Err(e2) => {
@@ -3418,6 +3599,7 @@ fn build_pipeline_with_retry(
     bitrate_kbps: u32,
     bit_depth: u8,
     plan: crate::session_plan::SessionPlan,
+    quit: &Arc<AtomicBool>,
 ) -> Result<Pipeline> {
     // ~10s first-frame wait per attempt. 8 gives a ~90s budget for the SLOW case: a host-managed
     // gamescope session cold-starting Steam Big Picture (the SteamOS/Bazzite takeover) can take
@@ -3444,7 +3626,7 @@ fn build_pipeline_with_retry(
     const MAX_ATTEMPTS: u32 = 8;
     let mut backoff = std::time::Duration::from_millis(500);
     for attempt in 1..=MAX_ATTEMPTS {
-        match build_pipeline(vd, mode, bitrate_kbps, bit_depth, plan) {
+        match build_pipeline(vd, mode, bitrate_kbps, bit_depth, plan, quit) {
             Ok(pipe) => {
                 if attempt > 1 {
                     tracing::info!(attempt, "pipeline up after retry");
@@ -3507,8 +3689,15 @@ fn build_pipeline(
     bitrate_kbps: u32,
     bit_depth: u8,
     plan: crate::session_plan::SessionPlan,
+    quit: &Arc<AtomicBool>,
 ) -> Result<Pipeline> {
-    let vout = vd.create(mode).context("create virtual output")?;
+    // Acquire through the registry (design/display-management.md): on Linux this pools the display
+    // for keep-alive (reuse a kept one, or create + keep the backend's keepalive so it outlives the
+    // session per policy); on Windows it delegates to `vd.create` (the manager already leases). The
+    // returned `VirtualOutput`'s keepalive is a registry lease — the capturer holds it as before. The
+    // `quit` flag rides into the lease so a deliberate-quit teardown skips the keep-alive linger.
+    let vout = crate::vdisplay::registry::acquire(vd, mode, quit.clone())
+        .context("create virtual output")?;
     // The backend reports the refresh it actually achieved in `preferred_mode.2` (KWin may cap a
     // virtual output at 60 Hz if the custom-mode install was rejected). Pace the encoder + frame
     // clock to that, not the requested rate, so we don't emit phantom duplicate frames over a
@@ -3581,6 +3770,43 @@ mod tests {
         assert!(adapt_fec(u32::MAX) <= FEC_MAX);
     }
 
+    #[test]
+    fn data_socket_defaults_to_random_hole_punch() {
+        // No fixed port (and the explicit-0 alias) → a random ephemeral port, and NOT direct: the
+        // caller hole-punches.
+        for req in [None, Some(0)] {
+            let (sock, direct) = bind_data_socket(req).expect("bind random data socket");
+            assert!(!direct, "req={req:?} must hole-punch, not stream direct");
+            assert_ne!(sock.local_addr().unwrap().port(), 0);
+        }
+    }
+
+    #[test]
+    fn data_socket_fixed_binds_direct_then_falls_back_when_busy() {
+        // Learn a currently-free port (bind :0, read it, drop — the same reserve-then-rebind the
+        // host itself uses; a race here would only make the assert below flaky, not wrong).
+        let free = std::net::UdpSocket::bind("0.0.0.0:0")
+            .unwrap()
+            .local_addr()
+            .unwrap()
+            .port();
+
+        // A free fixed port binds exactly it, in DIRECT mode (no hole-punch).
+        let (held, direct) = bind_data_socket(Some(free)).expect("bind fixed data socket");
+        assert!(direct, "a fixed --data-port must stream direct");
+        assert_eq!(held.local_addr().unwrap().port(), free);
+
+        // While it's held, a second session on the same fixed port can't bind it → it must fall
+        // back to a random port + hole-punch rather than fail (so concurrency never regresses).
+        let (fallback, direct2) = bind_data_socket(Some(free)).expect("busy fixed port falls back");
+        assert!(!direct2, "a busy fixed port must fall back to hole-punch");
+        assert_ne!(
+            fallback.local_addr().unwrap().port(),
+            free,
+            "the fallback must not reuse the busy fixed port"
+        );
+    }
+
     #[test]
     fn compositor_resolution_precedence() {
         use crate::vdisplay::Compositor::*;
@@ -3756,10 +3982,18 @@ mod tests {
     /// End-to-end through the C ABI — the exact contract platform clients (Swift) link:
     /// in-process punktfunk/1 host, `punktfunk_connect` (TOFU → pinned reconnect) →
     /// `punktfunk_connection_next_au` pulls verified frames → `punktfunk_connection_send_input`
+    /// In-process-host tests each spin up a host on a fixed loopback port and share the process-global
+    /// admission table, so they must NOT run concurrently: a same-identity connection in one test would
+    /// fire the reconnect-preempt (`preempt_same_identity`) against another test's live session and
+    /// close it. Serialize them on this lock. Poison-tolerant (`into_inner`) so a failing test doesn't
+    /// cascade a poison error into the others.
+    static SESSION_TEST_LOCK: std::sync::Mutex<()> = std::sync::Mutex::new(());
+
     /// enqueues → `punktfunk_connection_close`. Three sequential sessions against ONE host
     /// process prove the persistent listener, and a wrong pin is rejected.
     #[test]
     fn c_abi_connection_roundtrip() {
+        let _serial = SESSION_TEST_LOCK.lock().unwrap_or_else(|p| p.into_inner());
         use punktfunk_core::abi::{
             punktfunk_connect, punktfunk_connection_close, punktfunk_connection_mode,
             punktfunk_connection_send_input,
@@ -3778,6 +4012,8 @@ mod tests {
                 allow_pairing: false,
                 pairing_pin: None,
                 paired_store: None,
+                data_port: None,
+                idle_timeout: None,
             })
         });
         std::thread::sleep(std::time::Duration::from_millis(500));
@@ -3946,6 +4182,7 @@ mod tests {
     /// admitted to a session with no PIN and no reconnect.
     #[test]
     fn delegated_approval_admits_after_knock() {
+        let _serial = SESSION_TEST_LOCK.lock().unwrap_or_else(|p| p.into_inner());
         use punktfunk_core::client::NativeClient;
         use punktfunk_core::quic::endpoint;
 
@@ -3972,6 +4209,8 @@ mod tests {
                     allow_pairing: false,
                     pairing_pin: None,
                     paired_store: None, // unused: the shared `np` IS the store handle
+                    data_port: None,
+                    idle_timeout: None,
                 },
                 0, // no mgmt API in this test → advertise no `mgmt` mDNS port
                 np_host,
@@ -4055,6 +4294,7 @@ mod tests {
     /// identity gets a session on a pairing-required host; an anonymous client does not.
     #[test]
     fn pairing_ceremony_and_gate() {
+        let _serial = SESSION_TEST_LOCK.lock().unwrap_or_else(|p| p.into_inner());
         use punktfunk_core::client::NativeClient;
         use punktfunk_core::quic::endpoint;
 
@@ -4070,6 +4310,8 @@ mod tests {
                 allow_pairing: false,
                 pairing_pin: Some("4321".into()),
                 paired_store: Some(test_paired_path()),
+                data_port: None,
+                idle_timeout: None,
             })
         });
         std::thread::sleep(std::time::Duration::from_millis(500));

crates/punktfunk-host/src/vdisplay.rs

@@ -64,6 +64,43 @@ pub trait VirtualDisplay: Send {
     /// Default: no-op — only the Windows pf-vdisplay backend uses it (Linux compositors own their virtual
     /// output identity). `None` = anonymous/unpaired/GameStream → the backend's auto (slot-based) identity.
     fn set_client_identity(&mut self, _fingerprint: Option<[u8; 32]>) {}
+    /// The stable identity slot the backend resolved for the most recent [`create`](Self::create) —
+    /// the per-client id the identity policy assigned (`Some`), or `None` for shared/anonymous. The
+    /// registry reads it right after `create` to key the display's group **arrangement** (manual
+    /// per-slot positions) and to label the mgmt `/display/state` slot. Default `None`: a backend
+    /// with no per-client identity (Mutter/wlroots/gamescope) always auto-rows. Only KWin (per-slot
+    /// output naming) reports a real slot on Linux.
+    fn last_identity_slot(&self) -> Option<u32> {
+        None
+    }
+    /// Place the most-recently-[created](Self::create) output at `(x, y)` in the desktop coordinate
+    /// space (design `display-management.md` §6.2 — layout). The registry, which owns the display
+    /// **group**, computes the position from the whole group (auto-row or the console's manual
+    /// arrangement) and calls this right after `create`. Default no-op: only backends that can position
+    /// an output (KWin) implement it; the registry never calls it for the desktop origin `(0, 0)`, so a
+    /// single-display / first-of-group session issues no positioning at all. Best-effort — a failure
+    /// leaves the compositor's default placement.
+    fn apply_position(&mut self, _x: i32, _y: i32) {}
+    /// Take the topology **restore** action this [`create`](Self::create) prepared — the work that
+    /// un-does an `exclusive`/`primary` topology change (e.g. re-enable the physical outputs KWin
+    /// disabled). The registry lifts it into the display **group** so it runs **once, when the group's
+    /// last display is torn down** (design §6.1 — per-group restore), not when this one session's
+    /// display drops: a sibling `exclusive` session must not have the physical re-enabled under it.
+    /// Called right after `create`; the backend must not also run it itself. Default `None` — a backend
+    /// whose topology auto-reverts (Mutter `APPLY_TEMPORARY`) or that changes nothing has nothing to
+    /// hand off.
+    fn take_topology_restore(&mut self) -> Option<Box<dyn FnOnce() + Send>> {
+        None
+    }
+    /// Tell the backend whether this create will be the **first** display in its group — i.e. no
+    /// sibling of the same backend is already live (design §6.1). A backend that *establishes* the
+    /// group's topology (Mutter's sole-monitor `exclusive` `ApplyMonitorsConfig`) applies it only when
+    /// first; a later sibling **extends** into the already-exclusive desktop instead of re-clobbering it
+    /// (a fresh sole-monitor config would disable the first session's virtual output). Set by the
+    /// registry right before [`create`](Self::create). Default no-op: KWin recognises siblings at
+    /// runtime by output name (first-slot-wins + a group-aware disable filter), and single-display
+    /// backends never have a sibling.
+    fn set_first_in_group(&mut self, _first: bool) {}
 }
 
 /// Compositors punktfunk knows how to drive (plan §6).
@@ -403,21 +440,11 @@ pub fn apply_session_env(active: &ActiveSession) {
     if active.kind == ActiveKind::DesktopGnome {
         std::env::set_var("PUNKTFUNK_FORCE_SHM", "1");
     }
-    // Stream the desktop as the SOLE output: promote the per-session virtual output to PRIMARY so
+    // Topology (Stage 2): the per-compositor backends (KWin/Mutter) now read
-    // the panels + windows land on the streamed surface, not an unstreamed real output (the
+    // [`effective_topology`] directly at create time — the console policy, else the legacy
-    // auto-detected desktop path *is* "stream this desktop"). Default-on for the auto path; an
+    // `PUNKTFUNK_{KWIN,MUTTER}_VIRTUAL_PRIMARY` env, else the Auto default (exclusive on the
-    // explicit `PUNKTFUNK_{KWIN,MUTTER}_VIRTUAL_PRIMARY` still wins.
+    // auto-desktop path). So this connect-path no longer writes that env (one fewer process-env
-    match active.kind {
+    // mutation on the `ENV_LOCK` surface); `effective_topology()` computes the identical result.
-        ActiveKind::DesktopKde if std::env::var_os("PUNKTFUNK_KWIN_VIRTUAL_PRIMARY").is_none() => {
-            std::env::set_var("PUNKTFUNK_KWIN_VIRTUAL_PRIMARY", "1");
-        }
-        ActiveKind::DesktopGnome
-            if std::env::var_os("PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY").is_none() =>
-        {
-            std::env::set_var("PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY", "1");
-        }
-        _ => {}
-    }
 }
 #[cfg(not(target_os = "linux"))]
 pub fn apply_session_env(_active: &ActiveSession) {}
@@ -723,14 +750,87 @@ pub fn start_restore_worker() -> std::sync::Arc<()> {
     std::sync::Arc::new(())
 }
 
+// The user-configurable management policy (keep-alive / topology / conflict / identity / layout),
+// layered above the per-compositor backends — platform-neutral (the mgmt API + both host paths read
+// it), so no cfg gate. See `design/display-management.md`.
+#[path = "vdisplay/policy.rs"]
+pub(crate) mod policy;
+
+// The pure per-display lifecycle state machine (refcount + linger + pin), platform-neutral and
+// property-tested; the registry executes the side effects its transitions dictate.
+#[path = "vdisplay/lifecycle.rs"]
+pub(crate) mod lifecycle;
+
+// The neutral snapshot/release facade over the per-OS lifecycle owners (Windows manager; Linux pool
+// later), for the management API's /display/state + /display/release.
+#[path = "vdisplay/registry.rs"]
+pub(crate) mod registry;
+
+// The pure display-arrangement engine (auto-row / manual → per-member positions), platform-neutral
+// and unit-tested; the registry (state readout) and the KWin position apply consume it.
+#[path = "vdisplay/layout.rs"]
+pub(crate) mod layout;
+
+/// Resolve a [`policy::Topology`] to a concrete value (never [`policy::Topology::Auto`]). `Auto`
+/// reproduces today's default: **extend** under an explicit `PUNKTFUNK_COMPOSITOR` pin (the CI/test
+/// posture, where the host isn't the sole desktop), else **exclusive** (Windows + the auto-detected
+/// Linux desktop path, where "stream this desktop" means promoting the virtual output to sole).
+pub fn resolve_topology(t: policy::Topology) -> policy::Topology {
+    match t {
+        policy::Topology::Auto => {
+            if crate::config::config().compositor.is_some() {
+                policy::Topology::Extend
+            } else {
+                policy::Topology::Exclusive
+            }
+        }
+        concrete => concrete,
+    }
+}
+
+/// The concrete display topology for the current session — what the per-compositor backends (and the
+/// Windows isolate gate) apply at create time. Precedence, mirroring the rest of the policy surface:
+/// the **console policy** when configured, else the legacy **`PUNKTFUNK_{KWIN,MUTTER}_VIRTUAL_PRIMARY`**
+/// env (an operator's explicit choice — `1`→exclusive, `0`→extend), else the **Auto** default
+/// ([`resolve_topology`]: exclusive on the auto-detected desktop / Windows, extend under a compositor
+/// pin). Always resolved (never [`policy::Topology::Auto`]). This is the Stage-2 replacement for the
+/// `apply_session_env` boolean write — the backends read policy directly, so the `primary` level
+/// (distinct from `exclusive`) becomes expressible and one process-env mutation drops off the connect
+/// path.
+pub fn effective_topology() -> policy::Topology {
+    if let Some(e) = policy::prefs().configured_effective() {
+        return resolve_topology(e.topology);
+    }
+    // Unconfigured: honor a legacy operator env if present (a host runs one desktop backend, so at
+    // most one of these is set), else the Auto default.
+    let legacy = [
+        "PUNKTFUNK_KWIN_VIRTUAL_PRIMARY",
+        "PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY",
+    ]
+    .iter()
+    .find_map(|k| std::env::var(k).ok());
+    match legacy.as_deref().map(str::trim) {
+        Some("1" | "true" | "yes" | "on") => policy::Topology::Exclusive,
+        Some("0" | "false" | "no" | "off") => policy::Topology::Extend,
+        _ => resolve_topology(policy::Topology::Auto),
+    }
+}
+
 // Goal-1 stage 6: per-compositor Linux backends under `vdisplay/linux/`, the Windows IddCx/SudoVDA
 // backends under `vdisplay/windows/`; `#[path]` keeps the `crate::vdisplay::*` module names flat.
 #[cfg(target_os = "linux")]
 #[path = "vdisplay/linux/gamescope.rs"]
 mod gamescope;
-#[cfg(target_os = "windows")]
+// Platform-neutral per-client stable display-id map (Stage 3): Windows seeds the monitor EDID +
-#[path = "vdisplay/windows/identity.rs"]
+// ConnectorIndex from the id; KWin names its output from it. `allow(dead_code)` because only Windows
+// consumes it in non-test code today — the KWin wiring is the next Stage-3 step.
+#[allow(dead_code)]
+#[path = "vdisplay/identity.rs"]
 pub(crate) mod identity;
+// Platform-neutral mode-conflict admission (Stage 4): the separate/join/steal/reject decision + the
+// live-session registry, wired into the punktfunk/1 handshake.
+#[path = "vdisplay/admission.rs"]
+pub(crate) mod admission;
 #[cfg(target_os = "linux")]
 #[path = "vdisplay/linux/kwin.rs"]
 mod kwin;

crates/punktfunk-host/src/vdisplay/admission.rs

@@ -0,0 +1,278 @@
+//! Mode-conflict **admission** (design: `design/display-management.md` §5.3, Stage 4). When a
+//! *different* client connects while another client's session is already live, the `mode_conflict`
+//! policy decides what happens — BEFORE the Welcome / RTSP launch, so the client gets an honest answer
+//! instead of a mid-build failure:
+//!
+//! * `separate` — proceed on a fresh display at the requested mode (today's Linux multi-view / the
+//!   default; no behavior change unconfigured).
+//! * `join` — admit at the live display's mode (honest-downgrade: the Welcome carries the real mode).
+//! * `steal` — signal the victim session(s)' stop flag(s), wait the release grace, then serve.
+//! * `reject` — refuse with a typed handshake error naming the live mode + client.
+//!
+//! A **live-session registry** ([`register`]) lets the decision see the current sessions (identity +
+//! mode + stop flag); each session registers once admitted and drops its [`LiveGuard`] on end. The
+//! decision itself ([`decide`]) is pure over a session slice, so it is unit-tested exhaustively.
+
+use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
+use std::sync::{Arc, Mutex, OnceLock};
+
+use crate::vdisplay::policy::{self, ModeConflict};
+
+/// A currently-live session, as admission sees it.
+#[derive(Clone)]
+pub struct LiveSession {
+    id: u64,
+    /// The owning client's cert fingerprint (`None` = anonymous / no client cert presented).
+    pub identity: Option<[u8; 32]>,
+    pub mode: (u32, u32, u32),
+    /// The session's stop flag — signaled to preempt it on `steal`.
+    pub stop: Arc<AtomicBool>,
+    /// Short client label for `reject` messages.
+    pub label: String,
+}
+
+/// The admission outcome for a connecting session.
+#[derive(Debug)]
+pub enum Admission {
+    /// No conflict / `separate`: proceed on a fresh display at the requested mode.
+    Separate,
+    /// `join`: admit at this (live) mode — share the existing display (honest-downgrade).
+    Join((u32, u32, u32)),
+    /// `steal`: signal these victim stop flags, wait the release grace, then proceed at the requested mode.
+    Steal(Vec<Arc<AtomicBool>>),
+    /// `reject`: refuse with this reason (host-busy + live mode + client label).
+    Reject(String),
+}
+
+fn table() -> &'static Mutex<Vec<LiveSession>> {
+    static T: OnceLock<Mutex<Vec<LiveSession>>> = OnceLock::new();
+    T.get_or_init(|| Mutex::new(Vec::new()))
+}
+
+static NEXT_ID: AtomicU64 = AtomicU64::new(1);
+
+/// Two identities are the same client iff both are present and equal. Anonymous (`None`) never
+/// matches — we can't prove it's the same client, so two anonymous clients are treated as distinct
+/// (each conflicts), which is the safe side for `steal`/`reject`.
+fn same_client(a: Option<[u8; 32]>, b: Option<[u8; 32]>) -> bool {
+    matches!((a, b), (Some(x), Some(y)) if x == y)
+}
+
+/// The mode-conflict decision, pure over the live-session slice (so it's unit-testable). A conflict is
+/// a live session owned by a DIFFERENT client — a same-client reconnect adopts / reconfigures its own
+/// display and never conflicts (so it always resolves to `Separate` here and preempts downstream).
+pub fn decide(
+    conflict: ModeConflict,
+    req_identity: Option<[u8; 32]>,
+    live: &[LiveSession],
+) -> Admission {
+    let others: Vec<&LiveSession> = live
+        .iter()
+        .filter(|s| !same_client(s.identity, req_identity))
+        .collect();
+    if others.is_empty() {
+        return Admission::Separate; // no other client is live → no conflict
+    }
+    match conflict {
+        ModeConflict::Separate => Admission::Separate,
+        // Join at the OLDEST other session's mode (the established "primary" the desktop is built on).
+        ModeConflict::Join => Admission::Join(others[0].mode),
+        ModeConflict::Steal => {
+            Admission::Steal(others.iter().map(|s| Arc::clone(&s.stop)).collect())
+        }
+        ModeConflict::Reject => {
+            let v = others[0];
+            Admission::Reject(format!(
+                "host busy: streaming {}x{}@{} to {}",
+                v.mode.0, v.mode.1, v.mode.2, v.label
+            ))
+        }
+    }
+}
+
+/// The effective `mode_conflict` policy for THIS host: the console value (default `Separate` when
+/// unconfigured), with the **Windows default applied**. On Windows `separate` — including the
+/// unconfigured default — resolves to **`reject`**: two concurrent Windows sessions would both drive the
+/// SAME pf-vdisplay monitor's single-capturer IDD-push channel ("newest-delivery-wins"), which freezes
+/// the live client and can wedge the driver (true multi-session capture is §6.6 / Stage 7). So a 2nd
+/// client gets a clean 503 and the live session is protected; `join`/`steal` stay as explicit opt-ins.
+/// Linux keeps `separate` (real multi-view). Shared by the native + GameStream admission paths.
+pub fn effective_conflict() -> ModeConflict {
+    let conflict = policy::prefs()
+        .configured_effective()
+        .map(|e| e.mode_conflict)
+        .unwrap_or(ModeConflict::Separate);
+    #[cfg(windows)]
+    if matches!(conflict, ModeConflict::Separate) {
+        return ModeConflict::Reject;
+    }
+    conflict
+}
+
+/// Resolve the admission decision for a connecting native session: [`effective_conflict`] + [`decide`]
+/// against the live set.
+pub fn admit(req_identity: Option<[u8; 32]>) -> Admission {
+    decide(effective_conflict(), req_identity, &table().lock().unwrap())
+}
+
+/// Pure core of [`preempt_same_identity`]: the stop flags of live sessions owned by the SAME client
+/// as `req_identity` (its own zombies). Testable over a slice (the public fn locks the global table).
+fn same_identity_stops(
+    req_identity: Option<[u8; 32]>,
+    live: &[LiveSession],
+) -> Vec<Arc<AtomicBool>> {
+    live.iter()
+        .filter(|s| same_client(s.identity, req_identity))
+        .map(|s| Arc::clone(&s.stop))
+        .collect()
+}
+
+/// Preempt this reconnecting client's OWN still-live session(s). A client has at most one live
+/// session, so a new connection from an already-registered identity is a **reconnect** — the old
+/// session is a zombie whose QUIC idle timer hasn't fired yet (an unwanted disconnect is only
+/// declared dead after `max_idle_timeout`, ~seconds later). Return its stop flag(s) so the caller
+/// signals them and waits the release grace: the zombie tears its display down, which (keep-alive on)
+/// lingers, and THIS reconnect **reuses** that kept display instead of landing on a fresh SECOND one
+/// (the "thrown onto a second display while the old one keeps streaming" bug). Anonymous (`None`)
+/// never matches — same limitation as `steal`/`reject`. Call this BEFORE [`admit`] and before this
+/// session registers itself, so it only ever signals a *prior* session's flag, never its own.
+pub fn preempt_same_identity(req_identity: Option<[u8; 32]>) -> Vec<Arc<AtomicBool>> {
+    same_identity_stops(req_identity, &table().lock().unwrap())
+}
+
+/// Register a now-admitted, live session; the returned guard removes it on drop (session end). Call
+/// AFTER [`admit`] (so a session never conflicts with itself) and once the mode + stop flag are known.
+pub fn register(
+    identity: Option<[u8; 32]>,
+    mode: (u32, u32, u32),
+    stop: Arc<AtomicBool>,
+    label: String,
+) -> LiveGuard {
+    let id = NEXT_ID.fetch_add(1, Ordering::Relaxed);
+    table().lock().unwrap().push(LiveSession {
+        id,
+        identity,
+        mode,
+        stop,
+        label,
+    });
+    LiveGuard { id }
+}
+
+/// RAII handle: removes its live-session entry from the registry on drop (session end).
+pub struct LiveGuard {
+    id: u64,
+}
+
+impl Drop for LiveGuard {
+    fn drop(&mut self) {
+        table().lock().unwrap().retain(|s| s.id != self.id);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn sess(identity: Option<u8>, mode: (u32, u32, u32)) -> LiveSession {
+        LiveSession {
+            id: 0,
+            identity: identity.map(|n| {
+                let mut f = [0u8; 32];
+                f[0] = n;
+                f
+            }),
+            mode,
+            stop: Arc::new(AtomicBool::new(false)),
+            label: "peer".into(),
+        }
+    }
+    fn fp(n: u8) -> Option<[u8; 32]> {
+        let mut f = [0u8; 32];
+        f[0] = n;
+        Some(f)
+    }
+
+    #[test]
+    fn no_live_session_is_always_separate() {
+        for c in [
+            ModeConflict::Separate,
+            ModeConflict::Join,
+            ModeConflict::Steal,
+            ModeConflict::Reject,
+        ] {
+            assert!(matches!(decide(c, fp(1), &[]), Admission::Separate));
+        }
+    }
+
+    #[test]
+    fn same_client_never_conflicts() {
+        let live = [sess(Some(1), (2560, 1440, 60))];
+        // Even under reject/steal, the SAME client (fp 1) reconnecting is not a conflict.
+        assert!(matches!(
+            decide(ModeConflict::Reject, fp(1), &live),
+            Admission::Separate
+        ));
+        assert!(matches!(
+            decide(ModeConflict::Steal, fp(1), &live),
+            Admission::Separate
+        ));
+    }
+
+    #[test]
+    fn different_client_applies_policy() {
+        let live = [sess(Some(1), (2560, 1440, 60))];
+        assert!(matches!(
+            decide(ModeConflict::Separate, fp(2), &live),
+            Admission::Separate
+        ));
+        assert!(matches!(
+            decide(ModeConflict::Join, fp(2), &live),
+            Admission::Join((2560, 1440, 60))
+        ));
+        assert!(matches!(
+            decide(ModeConflict::Steal, fp(2), &live),
+            Admission::Steal(v) if v.len() == 1
+        ));
+        assert!(matches!(
+            decide(ModeConflict::Reject, fp(2), &live),
+            Admission::Reject(r) if r.contains("2560x1440@60")
+        ));
+    }
+
+    #[test]
+    fn two_anonymous_clients_conflict() {
+        // Anonymous (None) can't be proven same-client, so a second anon client DOES conflict.
+        let live = [sess(None, (1920, 1080, 60))];
+        assert!(matches!(
+            decide(ModeConflict::Reject, None, &live),
+            Admission::Reject(_)
+        ));
+    }
+
+    #[test]
+    fn same_identity_stops_targets_own_zombie_only() {
+        let live = [
+            sess(Some(1), (2560, 1440, 60)), // this client's prior (zombie) session
+            sess(Some(2), (1920, 1080, 60)), // a different client
+        ];
+        // Reconnecting as client 1 → its own zombie's stop is returned (to preempt), not client 2's.
+        assert_eq!(same_identity_stops(fp(1), &live).len(), 1);
+        // A client with no prior session (fp 3) has nothing of its own to preempt.
+        assert_eq!(same_identity_stops(fp(3), &live).len(), 0);
+        // Anonymous never matches — we can't prove it's the same client.
+        assert_eq!(same_identity_stops(None, &live).len(), 0);
+    }
+
+    #[test]
+    fn join_targets_the_oldest_other_session() {
+        let live = [
+            sess(Some(1), (3840, 2160, 60)), // oldest
+            sess(Some(2), (1280, 720, 120)),
+        ];
+        assert!(matches!(
+            decide(ModeConflict::Join, fp(3), &live),
+            Admission::Join((3840, 2160, 60))
+        ));
+    }
+}

crates/punktfunk-host/src/vdisplay/identity.rs

@@ -0,0 +1,246 @@
+//! Platform-neutral **per-client → stable display-id map** (design: `design/display-management.md`
+//! §5.4 — identity). A client that reconnects gets the SAME small stable id every time, so the
+//! desktop environment can key its per-display config (notably **DPI scaling**) to it and reapply it:
+//!
+//! * **Windows** seeds the pf-vdisplay monitor's EDID serial + IddCx `ConnectorIndex` from the id, so
+//!   Windows reapplies the client's saved `PerMonitorSettings` scaling. The id must stay `1..=15`
+//!   (`ConnectorIndex < MaxMonitorsSupported = 16`).
+//! * **KWin** names the streamed output `Virtual-punktfunk-<id>`; KWin persists per-output scale/mode
+//!   in `kwinoutputconfig.json` matched by name, so a stable per-client name makes KDE reapply that
+//!   client's scaling. (Generalised here from the Windows-only map; the KWin wiring is Stage 3.)
+//!
+//! The map key is a composable string ([`identity_key`]): the client cert fingerprint alone
+//! (`per-client`), or fingerprint + resolution (`per-client-mode` — distinct scaling per resolution).
+//! Anonymous/TOFU/GameStream sessions have no fingerprint and resolve to id `0` (auto) upstream,
+//! never reaching this map.
+//!
+//! Persisted to `<config>/display-identity.json` (migrated from the legacy Windows
+//! `pf-vdisplay-identity.json`) so ids — and the client→config association — survive host restarts.
+
+use std::path::PathBuf;
+use std::sync::{Mutex, OnceLock};
+
+use serde::{Deserialize, Serialize};
+
+/// Max stable id. Bounded by the Windows driver's use of the id as the IddCx `ConnectorIndex`
+/// (`< MaxMonitorsSupported = 16`), so ids run `1..=15` on every platform for a single shared map.
+const MAX_ID: u32 = 15;
+
+/// The map filename (migrated from the legacy Windows-only `pf-vdisplay-identity.json`).
+const FILE: &str = "display-identity.json";
+const LEGACY_FILE: &str = "pf-vdisplay-identity.json";
+
+/// Compose the map key for a client. `per_client_mode` appends the resolution so a client keeps a
+/// distinct id (and thus distinct persisted scaling) per resolution; otherwise the fingerprint alone.
+pub(crate) fn identity_key(fp: [u8; 32], mode: (u32, u32), per_client_mode: bool) -> String {
+    let hex: String = fp.iter().map(|b| format!("{b:02x}")).collect();
+    if per_client_mode {
+        format!("{hex}@{}x{}", mode.0, mode.1)
+    } else {
+        hex
+    }
+}
+
+#[derive(Serialize, Deserialize, Default)]
+struct Store {
+    /// Monotonic most-recently-used counter (the entry with the highest `seen` is the MRU). Persisted so
+    /// the LRU ordering survives host restarts.
+    tick: u64,
+    entries: Vec<Entry>,
+}
+
+#[derive(Serialize, Deserialize)]
+struct Entry {
+    /// The composed client key ([`identity_key`]) — the map key. (Serialized as `fp` for
+    /// back-compat with the legacy Windows `pf-vdisplay-identity.json`.)
+    #[serde(rename = "fp")]
+    key: String,
+    /// The client's stable display id (`1..=15`).
+    id: u32,
+    /// MRU stamp (compared against [`Store::tick`]).
+    seen: u64,
+}
+
+/// Persistent client-key → stable-id map (see the module docs).
+pub(crate) struct DisplayIdentityMap {
+    path: PathBuf,
+    store: Store,
+}
+
+impl DisplayIdentityMap {
+    /// Load the persisted map (empty on first run / unreadable / parse failure — a fresh map just
+    /// re-derives ids, costing a client one scaling re-set the first time). Migrates the legacy
+    /// Windows `pf-vdisplay-identity.json` if the new file is absent.
+    pub(crate) fn load() -> Self {
+        let dir = crate::gamestream::config_dir();
+        let path = dir.join(FILE);
+        let bytes = std::fs::read(&path)
+            .or_else(|_| std::fs::read(dir.join(LEGACY_FILE)))
+            .ok();
+        let mut store = bytes
+            .and_then(|b| serde_json::from_slice::<Store>(&b).ok())
+            .unwrap_or_default();
+        // SANITIZE a hand-edited / corrupt / cross-version file before trusting it: resolve()'s
+        // found-entry branch returns the stored id verbatim, so an out-of-range id (0 = the "auto"
+        // sentinel, or > MAX_ID) or a duplicate id/key would flow straight into the display identity.
+        // Drop out-of-range ids and dedup by BOTH key and id (keeping the most-recently-seen on a
+        // clash) so no two clients can map to the same id.
+        store.entries.sort_by_key(|e| std::cmp::Reverse(e.seen));
+        let mut seen_key = std::collections::HashSet::new();
+        let mut seen_id = std::collections::HashSet::new();
+        store.entries.retain(|e| {
+            (1..=MAX_ID).contains(&e.id) && seen_key.insert(e.key.clone()) && seen_id.insert(e.id)
+        });
+        Self { path, store }
+    }
+
+    /// The stable id (`1..=15`) for the client `key` ([`identity_key`]): its remembered id, or a
+    /// freshly assigned one (lowest free, else LRU-evict at the cap). Bumps the entry to MRU and persists.
+    pub(crate) fn resolve(&mut self, key: &str) -> u32 {
+        self.store.tick = self.store.tick.wrapping_add(1);
+        let now = self.store.tick;
+
+        if let Some(e) = self.store.entries.iter_mut().find(|e| e.key == key) {
+            e.seen = now;
+            let id = e.id;
+            self.persist();
+            return id;
+        }
+
+        // New client: prefer the lowest free id in 1..=MAX_ID; if all are taken, evict the LRU entry and
+        // reuse its id (the evicted client re-establishes its scaling once on its next connect).
+        let id = (1..=MAX_ID)
+            .find(|i| !self.store.entries.iter().any(|e| e.id == *i))
+            .unwrap_or_else(|| {
+                let lru = self
+                    .store
+                    .entries
+                    .iter()
+                    .enumerate()
+                    .min_by_key(|(_, e)| e.seen)
+                    .map(|(i, _)| i)
+                    .expect("entries are non-empty whenever every id 1..=MAX_ID is taken");
+                let evicted = self.store.entries.remove(lru);
+                evicted.id
+            });
+        self.store.entries.push(Entry {
+            key: key.to_string(),
+            id,
+            seen: now,
+        });
+        self.persist();
+        id
+    }
+
+    /// Persist atomically (temp file + rename). Best-effort: a write failure just means a restart may
+    /// re-derive an id (one scaling re-set). Not a credential, so a plain (non-ACL'd) write is fine.
+    fn persist(&self) {
+        let Ok(bytes) = serde_json::to_vec_pretty(&self.store) else {
+            return;
+        };
+        if let Some(dir) = self.path.parent() {
+            let _ = std::fs::create_dir_all(dir);
+        }
+        let tmp = self.path.with_extension("json.tmp");
+        if std::fs::write(&tmp, &bytes).is_ok() {
+            let _ = std::fs::rename(&tmp, &self.path);
+        }
+    }
+}
+
+/// The process-wide identity map (persisted, loaded once). Shared by the Windows manager and the
+/// Linux KWin backend — never in the same process (a host runs one platform), so one instance ⇒ no
+/// clobbering of the shared `display-identity.json`.
+pub(crate) fn global() -> &'static Mutex<DisplayIdentityMap> {
+    static MAP: OnceLock<Mutex<DisplayIdentityMap>> = OnceLock::new();
+    MAP.get_or_init(|| Mutex::new(DisplayIdentityMap::load()))
+}
+
+/// Resolve the connecting client's stable slot id per the `identity` policy. When no policy is
+/// configured, `default` applies — **PerClient on Windows / Shared on Linux**, preserving each
+/// platform's historical behavior (Windows always keyed monitors per-client; Linux used one shared
+/// output name). `None` ⇒ shared / anonymous → the backend uses its base name / auto slot.
+pub(crate) fn resolve_slot(
+    fp: Option<[u8; 32]>,
+    mode: (u32, u32),
+    default: crate::vdisplay::policy::Identity,
+) -> Option<u32> {
+    use crate::vdisplay::policy::Identity;
+    let id_policy = crate::vdisplay::policy::prefs()
+        .configured_effective()
+        .map(|e| e.identity)
+        .unwrap_or(default);
+    let per_client_mode = match id_policy {
+        Identity::Shared => return None,
+        Identity::PerClient => false,
+        Identity::PerClientMode => true,
+    };
+    let fp = fp?;
+    Some(
+        global()
+            .lock()
+            .unwrap()
+            .resolve(&identity_key(fp, mode, per_client_mode)),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn fp(n: u8) -> [u8; 32] {
+        let mut f = [0u8; 32];
+        f[0] = n;
+        f
+    }
+
+    fn temp_map(tag: &str) -> DisplayIdentityMap {
+        DisplayIdentityMap {
+            path: std::env::temp_dir().join(format!("pf-id-{tag}-{}.json", std::process::id())),
+            store: Store::default(),
+        }
+    }
+
+    #[test]
+    fn stable_across_calls_and_distinct_per_client() {
+        let mut m = temp_map("stable");
+        let a1 = m.resolve(&identity_key(fp(1), (1920, 1080), false));
+        let b = m.resolve(&identity_key(fp(2), (1920, 1080), false));
+        let a2 = m.resolve(&identity_key(fp(1), (1280, 720), false)); // per-client: mode ignored
+        assert_eq!(a1, a2, "same client → same id (per-client ignores mode)");
+        assert_ne!(a1, b, "distinct clients → distinct ids");
+        assert!((1..=MAX_ID).contains(&a1) && (1..=MAX_ID).contains(&b));
+        let _ = std::fs::remove_file(&m.path);
+    }
+
+    #[test]
+    fn per_client_mode_splits_by_resolution() {
+        let mut m = temp_map("permode");
+        let hd = m.resolve(&identity_key(fp(1), (1920, 1080), true));
+        let uhd = m.resolve(&identity_key(fp(1), (3840, 2160), true));
+        let hd2 = m.resolve(&identity_key(fp(1), (1920, 1080), true));
+        assert_ne!(hd, uhd, "same client, different resolution → different id");
+        assert_eq!(hd, hd2, "same client + resolution → same id");
+        let _ = std::fs::remove_file(&m.path);
+    }
+
+    #[test]
+    fn lru_eviction_reuses_an_id_at_the_cap() {
+        let mut m = temp_map("lru");
+        for n in 1..=15u8 {
+            m.resolve(&identity_key(fp(n), (1920, 1080), false));
+        }
+        let _ = m.resolve(&identity_key(fp(2), (1920, 1080), false)); // touch 2 so 1 is LRU
+        let id16 = m.resolve(&identity_key(fp(16), (1920, 1080), false));
+        assert!((1..=MAX_ID).contains(&id16));
+        assert_eq!(m.store.entries.len(), 15, "cap holds at 15 entries");
+        assert!(m.store.entries.iter().all(|e| (1..=MAX_ID).contains(&e.id)));
+        let _ = std::fs::remove_file(&m.path);
+    }
+
+    #[test]
+    fn key_composition() {
+        assert_eq!(identity_key(fp(0xab), (1920, 1080), false).len(), 64); // hex fp only
+        assert!(identity_key(fp(0xab), (1920, 1080), true).ends_with("@1920x1080"));
+    }
+}

crates/punktfunk-host/src/vdisplay/layout.rs

@@ -0,0 +1,142 @@
+//! Pure display-**arrangement** engine (design: `design/display-management.md` §6.2). Given a
+//! group's members (in acquire order) and the `layout` policy, compute each member's top-left
+//! origin in the desktop coordinate space. No I/O, no OS types — the registry (for the
+//! `/display/state` readout) and the per-backend position apply both consume it, so the auto-row /
+//! manual math is defined and tested in exactly one place (the `pick_gamescope_mode` / `wiring_plan`
+//! discipline).
+//!
+//! * **auto-row** — left-to-right in acquire order, top-aligned: member *i* sits at
+//!   `x = Σ widths[0..i]`, `y = 0`. This is what compositors mostly do by default, made
+//!   deterministic.
+//! * **manual** — per-identity-slot offsets from [`Layout::positions`] (console-arranged): a member
+//!   whose stable identity slot has a stored position sits there; a member with no pin (no stored
+//!   position, or a shared/anonymous identity that has no slot) falls back to its auto-row origin, so
+//!   a half-arranged group never collapses everything onto the origin.
+//!
+//! Group membership + acquire order live in the registry ([`super::registry`]); this file only turns
+//! that ordered member list into positions.
+
+use super::policy::{Layout, LayoutMode};
+
+/// One display in a group, as the arranger sees it (given in acquire order).
+#[derive(Clone, Copy, Debug)]
+pub struct Member {
+    /// Stable per-client identity slot — the manual-layout key. `None` for a shared/anonymous
+    /// identity (no per-client slot), which can't carry a manual pin and therefore always auto-rows.
+    pub identity_slot: Option<u32>,
+    /// Pixel width, for auto-row `x` accumulation. Clamped at 0 (a bogus negative never shifts a
+    /// sibling left).
+    pub width: i32,
+}
+
+/// A member's resolved desktop-space top-left origin.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct Placement {
+    pub x: i32,
+    pub y: i32,
+}
+
+/// The auto-row origin of member `i`: the summed width of every prior member, top-aligned.
+fn auto_row_x(members: &[Member], i: usize) -> i32 {
+    members[..i].iter().map(|m| m.width.max(0)).sum()
+}
+
+/// Arrange `members` (in acquire order) per `layout`, returning one [`Placement`] per member in the
+/// same order. Pure — the single source of truth for auto-row / manual placement, shared by the
+/// state readout and (KWin) the per-backend position apply.
+pub fn arrange(members: &[Member], layout: &Layout) -> Vec<Placement> {
+    members
+        .iter()
+        .enumerate()
+        .map(|(i, m)| {
+            let auto = Placement {
+                x: auto_row_x(members, i),
+                y: 0,
+            };
+            match layout.mode {
+                LayoutMode::AutoRow => auto,
+                // A pinned member sits at its stored offset; an unpinned one falls back to auto-row.
+                LayoutMode::Manual => m
+                    .identity_slot
+                    .and_then(|slot| layout.positions.get(&slot.to_string()))
+                    .map(|p| Placement { x: p.x, y: p.y })
+                    .unwrap_or(auto),
+            }
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::vdisplay::policy::Position;
+    use std::collections::BTreeMap;
+
+    fn m(slot: Option<u32>, width: i32) -> Member {
+        Member {
+            identity_slot: slot,
+            width,
+        }
+    }
+
+    fn manual(pairs: &[(&str, i32, i32)]) -> Layout {
+        let mut positions = BTreeMap::new();
+        for (k, x, y) in pairs {
+            positions.insert(k.to_string(), Position { x: *x, y: *y });
+        }
+        Layout {
+            mode: LayoutMode::Manual,
+            positions,
+        }
+    }
+
+    #[test]
+    fn auto_row_accumulates_widths_top_aligned() {
+        let members = [m(Some(1), 2560), m(Some(2), 1920), m(None, 1280)];
+        let out = arrange(&members, &Layout::default()); // default = AutoRow
+        assert_eq!(
+            out,
+            vec![
+                Placement { x: 0, y: 0 },
+                Placement { x: 2560, y: 0 },
+                Placement { x: 4480, y: 0 },
+            ]
+        );
+    }
+
+    #[test]
+    fn manual_honors_pins_by_identity_slot() {
+        let members = [m(Some(1), 2560), m(Some(7), 1920)];
+        // Client 7 arranged to the LEFT of client 1 (crossing order reversed vs auto-row).
+        let layout = manual(&[("1", 1920, 0), ("7", 0, 0)]);
+        let out = arrange(&members, &layout);
+        assert_eq!(out[0], Placement { x: 1920, y: 0 });
+        assert_eq!(out[1], Placement { x: 0, y: 0 });
+    }
+
+    #[test]
+    fn manual_unpinned_and_slotless_fall_back_to_auto_row() {
+        let members = [m(Some(1), 2560), m(Some(9), 1920), m(None, 1280)];
+        // Only slot 1 is pinned; slot 9 has no stored pin; the third has no slot at all.
+        let layout = manual(&[("1", 100, 50)]);
+        let out = arrange(&members, &layout);
+        assert_eq!(out[0], Placement { x: 100, y: 50 }, "pinned");
+        assert_eq!(out[1], Placement { x: 2560, y: 0 }, "unpinned → auto-row");
+        assert_eq!(out[2], Placement { x: 4480, y: 0 }, "slotless → auto-row");
+    }
+
+    #[test]
+    fn empty_group_is_empty() {
+        assert!(arrange(&[], &Layout::default()).is_empty());
+        assert!(arrange(&[], &manual(&[("1", 0, 0)])).is_empty());
+    }
+
+    #[test]
+    fn negative_width_never_shifts_siblings_left() {
+        let members = [m(Some(1), -100), m(Some(2), 1920)];
+        let out = arrange(&members, &Layout::default());
+        let origin = Placement { x: 0, y: 0 };
+        assert_eq!(out[0], origin);
+        assert_eq!(out[1], origin, "clamped width contributes 0");
+    }
+}

crates/punktfunk-host/src/vdisplay/lifecycle.rs

@@ -0,0 +1,338 @@
+//! Pure per-display **lifecycle state machine** (design: `design/display-management.md` §3).
+//!
+//! One virtual display's earned refcount + linger + pin state, with **no I/O and no OS-specific
+//! types** — the registry ([`super::registry`]) executes the side effects (backend create /
+//! teardown / linger timer) that this machine's transitions dictate. Extracted so the lifecycle
+//! logic is unit- and property-testable in isolation, and so the Linux registry and (later) the
+//! Windows manager share one audited machine instead of each re-deriving refcount+linger by hand.
+//!
+//! It is the platform-neutral distillation of the model the Windows `VirtualDisplayManager` already
+//! runs on glass: `Idle → Active{refs} → Lingering{until} → Idle`, plus a `Pinned` state for
+//! keep-alive-forever. The registry pairs one [`State`] with the owned backend resource; the machine
+//! only tracks the discriminant + refcount + deadline and reports what to do.
+
+use std::time::Instant;
+
+use super::policy::Linger;
+
+/// The lifecycle state of one virtual-display slot.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Default)]
+pub enum State {
+    /// No display exists.
+    #[default]
+    Idle,
+    /// A display exists with `refs` live sessions holding it.
+    Active { refs: u32 },
+    /// The last session left; the display is kept until `until`, then torn down.
+    Lingering { until: Instant },
+    /// The last session left; the display is kept indefinitely (keep-alive forever), until an
+    /// explicit release.
+    Pinned,
+}
+
+/// What acquiring a slot means for the backend.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Acquire {
+    /// The slot was empty — the backend must CREATE a fresh display.
+    Create,
+    /// The slot was already Active — another session JOINS the live display (refcount++).
+    Join,
+    /// The slot was kept alive (Lingering/Pinned) — REUSE the existing display (re-attach capture).
+    Reuse,
+}
+
+/// What releasing a hold on a slot means for the backend.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Release {
+    /// Another session still holds the display — nothing to do.
+    Decref,
+    /// The last session left; keep the display until its deadline ([`State::Lingering`]), then tear down.
+    Linger,
+    /// The last session left; keep the display indefinitely ([`State::Pinned`]).
+    Pin,
+    /// The last session left and keep-alive is off — tear the display down now.
+    Teardown,
+    /// A release with no live hold (stale/duplicate) — no-op.
+    Noop,
+}
+
+impl State {
+    /// True while a backend display resource exists (Active/Lingering/Pinned) — the registry holds
+    /// the keepalive in exactly these states, and `Idle` means it has been dropped.
+    pub fn has_display(self) -> bool {
+        !matches!(self, State::Idle)
+    }
+
+    /// Number of live sessions holding the display (0 unless Active).
+    pub fn refs(self) -> u32 {
+        match self {
+            State::Active { refs } => refs,
+            _ => 0,
+        }
+    }
+
+    /// A session acquires the slot. Transitions the state and reports whether the backend must
+    /// create a fresh display, join the live one, or reuse the kept one.
+    pub fn acquire(&mut self) -> Acquire {
+        match *self {
+            State::Idle => {
+                *self = State::Active { refs: 1 };
+                Acquire::Create
+            }
+            State::Active { refs } => {
+                *self = State::Active { refs: refs + 1 };
+                Acquire::Join
+            }
+            State::Lingering { .. } | State::Pinned => {
+                *self = State::Active { refs: 1 };
+                Acquire::Reuse
+            }
+        }
+    }
+
+    /// A session releases the slot. When the LAST session leaves, `now` + the resolved `linger`
+    /// decide the kept state. Returns what the registry should do.
+    pub fn release(&mut self, now: Instant, linger: Linger) -> Release {
+        match *self {
+            State::Active { refs } if refs > 1 => {
+                *self = State::Active { refs: refs - 1 };
+                Release::Decref
+            }
+            State::Active { .. } => match linger {
+                Linger::Immediate => {
+                    *self = State::Idle;
+                    Release::Teardown
+                }
+                Linger::For(d) => {
+                    *self = State::Lingering { until: now + d };
+                    Release::Linger
+                }
+                Linger::Forever => {
+                    *self = State::Pinned;
+                    Release::Pin
+                }
+            },
+            // Releasing a slot with no live hold is a stale/duplicate release. The registry's
+            // gen-stamped leases already make a stale lease's drop a no-op before it reaches here;
+            // this is the defensive backstop.
+            State::Idle | State::Lingering { .. } | State::Pinned => Release::Noop,
+        }
+    }
+
+    /// The registry's linger-timer tick: a Lingering slot past its deadline goes Idle and returns
+    /// `true` (the registry tears the display down). Pinned and every other state are untouched.
+    pub fn poll_expiry(&mut self, now: Instant) -> bool {
+        match *self {
+            State::Lingering { until } if now >= until => {
+                *self = State::Idle;
+                true
+            }
+            _ => false,
+        }
+    }
+
+    /// Force-release a kept display (the `/display/release` endpoint): a Lingering/Pinned slot goes
+    /// Idle and the registry tears it down (`true`). An Active slot is refused (`false`) — releasing
+    /// a display that still has live sessions is session management, not display management. Idle → `false`.
+    pub fn force_release(&mut self) -> bool {
+        match *self {
+            State::Lingering { .. } | State::Pinned => {
+                *self = State::Idle;
+                true
+            }
+            State::Active { .. } | State::Idle => false,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::time::Duration;
+
+    #[test]
+    fn create_join_reuse_and_teardown() {
+        let mut s = State::default();
+        assert_eq!(s.acquire(), Acquire::Create);
+        assert_eq!(s, State::Active { refs: 1 });
+        // A concurrent session joins.
+        assert_eq!(s.acquire(), Acquire::Join);
+        assert_eq!(s.refs(), 2);
+        // One leaves — still active.
+        let now = Instant::now();
+        assert_eq!(s.release(now, Linger::Immediate), Release::Decref);
+        assert_eq!(s.refs(), 1);
+        // The last leaves with keep-alive off — teardown.
+        assert_eq!(s.release(now, Linger::Immediate), Release::Teardown);
+        assert_eq!(s, State::Idle);
+        assert!(!s.has_display());
+    }
+
+    #[test]
+    fn linger_then_reuse_within_window() {
+        let mut s = State::default();
+        let t0 = Instant::now();
+        s.acquire();
+        assert_eq!(
+            s.release(t0, Linger::For(Duration::from_secs(10))),
+            Release::Linger
+        );
+        assert!(s.has_display());
+        // A tick before the deadline does nothing.
+        assert!(!s.poll_expiry(t0 + Duration::from_secs(5)));
+        // A reconnect inside the window reuses the kept display.
+        assert_eq!(s.acquire(), Acquire::Reuse);
+        assert_eq!(s, State::Active { refs: 1 });
+    }
+
+    #[test]
+    fn linger_expires_to_teardown() {
+        let mut s = State::default();
+        let t0 = Instant::now();
+        s.acquire();
+        s.release(t0, Linger::For(Duration::from_secs(10)));
+        // Past the deadline → teardown.
+        assert!(s.poll_expiry(t0 + Duration::from_secs(11)));
+        assert_eq!(s, State::Idle);
+        // A second tick is idempotent (nothing to tear down).
+        assert!(!s.poll_expiry(t0 + Duration::from_secs(12)));
+    }
+
+    #[test]
+    fn pinned_never_expires_but_force_releases() {
+        let mut s = State::default();
+        let t0 = Instant::now();
+        s.acquire();
+        assert_eq!(s.release(t0, Linger::Forever), Release::Pin);
+        assert_eq!(s, State::Pinned);
+        // No amount of ticking tears a pinned display down.
+        assert!(!s.poll_expiry(t0 + Duration::from_secs(86_400)));
+        assert!(s.has_display());
+        // Only an explicit release does.
+        assert!(s.force_release());
+        assert_eq!(s, State::Idle);
+    }
+
+    #[test]
+    fn force_release_refuses_active() {
+        let mut s = State::default();
+        s.acquire();
+        assert!(
+            !s.force_release(),
+            "an active display can't be force-released"
+        );
+        assert_eq!(s.refs(), 1);
+        // Idle also can't.
+        let mut idle = State::default();
+        assert!(!idle.force_release());
+    }
+
+    #[test]
+    fn stale_release_is_noop() {
+        let mut s = State::default();
+        assert_eq!(s.release(Instant::now(), Linger::Immediate), Release::Noop);
+        assert_eq!(s, State::Idle);
+    }
+
+    /// Property test (deterministic seeded walk): across an arbitrary interleaving of acquire /
+    /// release / expiry-tick / force-release, the machine must never (a) leak or double-free the
+    /// backend resource — `has_display()` must exactly track a shadow "resource alive" flag, with
+    /// every Create preceded by no live resource and every teardown preceded by one — nor (b)
+    /// underflow the refcount, nor (c) tear a display down while a session still holds it.
+    #[test]
+    fn property_no_leaks_no_double_free_no_underflow() {
+        // Tiny deterministic LCG (Numerical Recipes) — reproducible, no dependency.
+        let mut rng: u64 = 0x1234_5678_9abc_def0;
+        let mut next = || {
+            rng = rng
+                .wrapping_mul(6364136223846793005)
+                .wrapping_add(1442695040888963407);
+            (rng >> 33) as u32
+        };
+
+        let base = Instant::now();
+        let mut logical_ms: u64 = 0;
+        let mut s = State::default();
+        // Shadow model.
+        let mut resource_alive = false;
+        let mut live_holds: u32 = 0;
+
+        for _ in 0..200_000 {
+            // Advance logical time by 0..2000 ms each step so lingers cross their deadlines.
+            logical_ms += (next() % 2000) as u64;
+            let now = base + Duration::from_millis(logical_ms);
+
+            match next() % 5 {
+                0 => {
+                    // acquire
+                    let before_alive = resource_alive;
+                    let a = s.acquire();
+                    match a {
+                        Acquire::Create => {
+                            assert!(!before_alive, "Create while a resource was alive")
+                        }
+                        Acquire::Join | Acquire::Reuse => {
+                            assert!(before_alive, "Join/Reuse with no live resource")
+                        }
+                    }
+                    resource_alive = true;
+                    live_holds += 1;
+                }
+                1 | 2 => {
+                    // release (weighted 2/5 so refs actually drain)
+                    let linger = match next() % 3 {
+                        0 => Linger::Immediate,
+                        1 => Linger::For(Duration::from_millis((next() % 3000) as u64 + 1)),
+                        _ => Linger::Forever,
+                    };
+                    let held_before = live_holds;
+                    let r = s.release(now, linger);
+                    match r {
+                        Release::Noop => assert_eq!(held_before, 0, "Noop only with no live hold"),
+                        Release::Decref => {
+                            assert!(held_before >= 2, "Decref must leave the display held");
+                            live_holds -= 1;
+                        }
+                        Release::Teardown => {
+                            assert_eq!(held_before, 1, "Teardown only on the last hold");
+                            live_holds = 0;
+                            resource_alive = false;
+                        }
+                        Release::Linger | Release::Pin => {
+                            assert_eq!(held_before, 1, "Linger/Pin only on the last hold");
+                            live_holds = 0;
+                            // resource stays alive (kept)
+                        }
+                    }
+                }
+                3 => {
+                    // expiry tick
+                    if s.poll_expiry(now) {
+                        assert_eq!(live_holds, 0, "expiry tore down a held display");
+                        resource_alive = false;
+                    }
+                }
+                _ => {
+                    // force release
+                    if s.force_release() {
+                        assert_eq!(live_holds, 0, "force-release tore down a held display");
+                        resource_alive = false;
+                    }
+                }
+            }
+
+            // Invariant after every step: the machine's own view of "a display exists" matches the
+            // shadow, and the refcount matches the live-hold count.
+            assert_eq!(
+                s.has_display(),
+                resource_alive,
+                "has_display drifted from the shadow model"
+            );
+            assert_eq!(
+                s.refs(),
+                live_holds,
+                "refs drifted from the live-hold count"
+            );
+        }
+    }
+}

crates/punktfunk-host/src/vdisplay/linux/kwin.rs

@@ -67,13 +67,42 @@ const VOUT_NAME: &str = "punktfunk";
 /// event (deprecated only since v6) for the node id, so cap the bind at 5.
 const MAX_VERSION: u32 = 5;
 
-/// The KWin virtual-display driver. Stateless — each [`create`](VirtualDisplay::create) spins up
+/// The KWin virtual-display driver. Carries the connecting client's cert fingerprint (set before
-/// its own Wayland connection/thread that owns the resulting output.
+/// [`create`](VirtualDisplay::create)) so a paired client gets a STABLE per-slot output NAME
-pub struct KwinDisplay;
+/// (`Virtual-punktfunk-<id>`) — KWin persists per-output config (scale/mode) keyed by name in
+/// `kwinoutputconfig.json`, so a stable name makes KDE reapply that client's scaling on reconnect
+/// (Stage 3). Each `create` spins up its own Wayland connection/thread that owns the output.
+#[derive(Default)]
+pub struct KwinDisplay {
+    client_fp: Option<[u8; 32]>,
+    /// The identity slot the last [`create`](VirtualDisplay::create) resolved (the per-client id, or
+    /// `None` for shared/anonymous) — reported to the registry via [`last_identity_slot`] so it can key
+    /// the group arrangement + `/display/state` slot to the same id this backend named the output with.
+    last_slot: Option<u32>,
+    /// The base output name the last `create` used (`punktfunk` / `punktfunk-<id>`) — so
+    /// [`apply_position`](VirtualDisplay::apply_position) can address the KWin output `Virtual-<name>`.
+    last_name: Option<String>,
+    /// The topology-restore action the last `create` prepared (re-enable the outputs an `exclusive`
+    /// topology disabled), pending pickup by the registry via [`take_topology_restore`] — so the
+    /// physical is re-enabled only when the display GROUP's last member drops (§6.1), not this session's.
+    /// A backstop [`Drop`] runs it if the registry never took it (so a physical is never left dark).
+    pending_restore: Option<Box<dyn FnOnce() + Send>>,
+}
+
+impl Drop for KwinDisplay {
+    fn drop(&mut self) {
+        // Backstop only: the registry takes the restore right after `create` (moving it into the group),
+        // so this is normally `None`. If some path skipped the take, re-enable here so a physical is
+        // never stranded dark.
+        if let Some(restore) = self.pending_restore.take() {
+            restore();
+        }
+    }
+}
 
 impl KwinDisplay {
     pub fn new() -> Result<Self> {
-        Ok(KwinDisplay)
+        Ok(KwinDisplay::default())
     }
 }
 
@@ -82,14 +111,61 @@ impl VirtualDisplay for KwinDisplay {
         "kwin"
     }
 
+    fn set_client_identity(&mut self, fingerprint: Option<[u8; 32]>) {
+        self.client_fp = fingerprint;
+    }
+
+    fn last_identity_slot(&self) -> Option<u32> {
+        self.last_slot
+    }
+
+    fn take_topology_restore(&mut self) -> Option<Box<dyn FnOnce() + Send>> {
+        self.pending_restore.take()
+    }
+
+    fn apply_position(&mut self, x: i32, y: i32) {
+        let Some(name) = self.last_name.clone() else {
+            return;
+        };
+        let output = format!("Virtual-{name}");
+        // kscreen-doctor position syntax: `output.<name>.position.<x>,<y>`.
+        let ok = std::process::Command::new("kscreen-doctor")
+            .arg(format!("output.{output}.position.{x},{y}"))
+            .status()
+            .map(|s| s.success())
+            .unwrap_or(false);
+        if ok {
+            tracing::info!(output, x, y, "KWin: placed output in the desktop layout");
+        } else {
+            tracing::warn!(output, x, y, "KWin: output position apply failed");
+        }
+    }
+
     fn create(&mut self, mode: Mode) -> Result<VirtualOutput> {
+        // Per-slot output name (Stage 3): the `identity` policy resolves the client to a stable id →
+        // `punktfunk-<id>` (KWin exposes `Virtual-punktfunk-<id>`, whose per-output config KWin
+        // persists by name). Shared / anonymous → the base `punktfunk` (today's single name). Linux
+        // defaults to Shared when unconfigured, so this is a no-op change until a policy opts in — AND
+        // it fixes the latent clash where two concurrent sessions both used `Virtual-punktfunk`.
+        let slot = crate::vdisplay::identity::resolve_slot(
+            self.client_fp,
+            (mode.width, mode.height),
+            crate::vdisplay::policy::Identity::Shared,
+        );
+        self.last_slot = slot; // reported to the registry for the group arrangement + state slot
+        let name = match slot {
+            Some(id) => format!("{VOUT_NAME}-{id}"),
+            None => VOUT_NAME.to_string(),
+        };
+        self.last_name = Some(name.clone()); // for apply_position (registry-driven §6.2 layout)
         let (setup_tx, setup_rx) = std::sync::mpsc::channel::<Result<u32, String>>();
         let stop = Arc::new(AtomicBool::new(false));
         let stop_thread = stop.clone();
         let (width, height) = (mode.width, mode.height);
+        let name_thread = name.clone();
         thread::Builder::new()
             .name("punktfunk-kwin-vout".into())
-            .spawn(move || virtual_output_thread(width, height, setup_tx, stop_thread))
+            .spawn(move || virtual_output_thread(width, height, name_thread, setup_tx, stop_thread))
             .context("spawn KWin virtual-output thread")?;
 
         let node_id = match setup_rx.recv_timeout(Duration::from_secs(20)) {
@@ -107,36 +183,70 @@ impl VirtualDisplay for KwinDisplay {
         // rejected custom mode leaves the output at 60 Hz). At ≤60 Hz there's nothing to install —
         // the source runs 60 Hz and the encoder downsamples — so carry the requested rate through.
         let achieved_hz = if mode.refresh_hz > 60 {
-            set_custom_refresh(width, height, mode.refresh_hz)
+            set_custom_refresh(width, height, mode.refresh_hz, &name)
         } else {
             mode.refresh_hz
         };
-        // Make our streamed output the SOLE desktop: plasmashell + windows land on the surface we
+        // Display-management topology (Stage 2): `Extend` leaves the streamed output an extension;
-        // stream, not on the headless session's `kwin --virtual` bootstrap output (otherwise the
+        // `Primary` makes it the primary output but keeps the bootstrap/physical outputs enabled;
-        // client sees only the wallpaper of an empty extended output). Opt-in
+        // `Exclusive` makes it the SOLE desktop (others disabled, restored on teardown) — so
-        // (PUNKTFUNK_KWIN_VIRTUAL_PRIMARY), mirroring the Mutter backend's PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY.
+        // plasmashell + windows land on the streamed surface, not the headless `kwin --virtual`
-        let restore = if virtual_primary_enabled() {
+        // bootstrap output. Read from the policy (replacing the PUNKTFUNK_KWIN_VIRTUAL_PRIMARY boolean).
-            apply_virtual_primary()
+        use crate::vdisplay::policy::Topology;
-        } else {
+        let disabled = match crate::vdisplay::effective_topology() {
-            Vec::new()
+            Topology::Exclusive => apply_virtual_primary(&name),
+            Topology::Primary => {
+                apply_virtual_primary_only(&name);
+                Vec::new() // nothing disabled → nothing to restore
+            }
+            Topology::Extend | Topology::Auto => Vec::new(),
         };
+        // Per-group restore (§6.1): DON'T bind the re-enable to this session's keepalive (a per-session
+        // `StopGuard` restore would re-enable the physical the moment the FIRST of several exclusive
+        // sessions drops — under a still-live sibling). Instead stash it as a closure the registry lifts
+        // into the display group and runs once, when the group's LAST member is torn down (ordered before
+        // that display's output is reclaimed, so KWin never sees zero outputs). Empty ⇒ nothing to restore.
+        self.pending_restore = (!disabled.is_empty()).then(|| {
+            let disabled = disabled.clone();
+            Box::new(move || reenable_outputs(&disabled)) as Box<dyn FnOnce() + Send>
+        });
+        // Layout position (§6.2) is applied by the registry via `apply_position` right after create
+        // (it owns the display group, so it computes auto-row / manual placement over the whole group).
         Ok(VirtualOutput {
             node_id,
             remote_fd: None,
             preferred_mode: Some((mode.width, mode.height, achieved_hz)),
-            keepalive: Box::new(StopGuard { stop, restore }),
+            keepalive: Box::new(StopGuard { stop }),
         })
     }
 }
 
+/// Re-enable the outputs an `exclusive` topology disabled (bootstrap / physical), so KWin re-homes onto
+/// them. Called by the registry when the display group's last member is torn down (design §6.1), BEFORE
+/// that member's output is reclaimed — so KWin is never momentarily left with zero enabled outputs.
+fn reenable_outputs(outputs: &[String]) {
+    if outputs.is_empty() {
+        return;
+    }
+    let args: Vec<String> = outputs
+        .iter()
+        .map(|o| format!("output.{o}.enable"))
+        .collect();
+    let _ = std::process::Command::new("kscreen-doctor")
+        .args(&args)
+        .status();
+    std::thread::sleep(Duration::from_millis(200));
+    tracing::info!(reenabled = ?outputs, "KWin: restored the physical/bootstrap outputs (group empty)");
+}
+
 /// Best-effort: raise the just-created virtual output's refresh above KWin's default 60 Hz by
 /// installing + selecting a custom mode via `kscreen-doctor` (the output is `Virtual-<VOUT_NAME>`,
 /// refresh given in mHz), then **read back the active mode** and return the refresh KWin actually
 /// gave us. The apply command can report success yet leave the output at 60 Hz (mode rejected),
 /// and a silent rate mismatch surfaces downstream as judder / duplicated frames — so the caller
 /// paces the encoder to the *achieved* rate, not the requested one.
-fn set_custom_refresh(width: u32, height: u32, hz: u32) -> u32 {
+fn set_custom_refresh(width: u32, height: u32, hz: u32, name: &str) -> u32 {
-    let output = format!("Virtual-{VOUT_NAME}");
+    let output = format!("Virtual-{name}");
     let mhz = hz.saturating_mul(1000);
     let run = |arg: String| {
         std::process::Command::new("kscreen-doctor")
@@ -213,26 +323,17 @@ fn read_active_refresh(output: &str) -> Option<u32> {
     Some(hz.round() as u32)
 }
 
-/// Opt-in: make the per-session virtual output the sole desktop. Off by default — a host with no
+/// The prefix EVERY managed KWin output shares — Stage 3 names them `punktfunk` / `punktfunk-<id>`,
-/// competing output (or one that wants the bootstrap kept) is unaffected; the headless KDE appliance
+/// which KWin exposes as `Virtual-punktfunk` / `Virtual-punktfunk-<id>`. Group membership (§6.1) is
-/// (run-headless-kde.sh's `kwin --virtual` bootstrap + our streamed output) sets it so the desktop
+/// recognised by this prefix, so we never have to thread the live set through the backend.
-/// renders on the streamed surface, not the bootstrap. Mirrors the Mutter backend's gate.
+const MANAGED_PREFIX: &str = "Virtual-punktfunk";
-fn virtual_primary_enabled() -> bool {
-    std::env::var("PUNKTFUNK_KWIN_VIRTUAL_PRIMARY")
-        .map(|v| {
-            matches!(
-                v.trim().to_ascii_lowercase().as_str(),
-                "1" | "true" | "yes" | "on"
-            )
-        })
-        .unwrap_or(false)
-}
 
-/// Names of currently-ENABLED outputs other than our `Virtual-punktfunk` — i.e. the headless
+/// Names of currently-ENABLED outputs that are **not managed by us** — the headless session's
-/// session's bootstrap output(s), which hold the desktop by default. Parsed from `kscreen-doctor -j`
+/// bootstrap output(s) + any physical monitor, i.e. exactly what `exclusive` must disable.
-/// (same source as [`read_active_refresh`]).
+/// **Group-aware (§6.1):** excludes the WHOLE managed family (the [`MANAGED_PREFIX`]), not just this
+/// session's own output — so a 2nd `exclusive` session (with a distinct per-slot name) never disables
+/// the 1st session's live output. Parsed from `kscreen-doctor -j` (same source as [`read_active_refresh`]).
 fn other_enabled_outputs() -> Vec<String> {
-    let ours = format!("Virtual-{VOUT_NAME}");
     let out = match std::process::Command::new("kscreen-doctor")
         .arg("-j")
         .output()
@@ -248,22 +349,49 @@ fn other_enabled_outputs() -> Vec<String> {
         .and_then(|o| o.as_array())
         .map(|outs| {
             outs.iter()
-                .filter(|o| {
+                .filter(|o| o.get("enabled").and_then(|e| e.as_bool()).unwrap_or(false))
-                    o.get("enabled").and_then(|e| e.as_bool()).unwrap_or(false)
+                .filter_map(|o| o.get("name").and_then(|n| n.as_str()))
-                        && o.get("name").and_then(|n| n.as_str()) != Some(ours.as_str())
+                .filter(|n| !n.starts_with(MANAGED_PREFIX))
-                })
+                .map(String::from)
-                .filter_map(|o| o.get("name").and_then(|n| n.as_str()).map(String::from))
                 .collect()
         })
         .unwrap_or_default()
 }
 
-/// Set `Virtual-punktfunk` primary and disable the bootstrap output(s) so it becomes the sole
+/// True if any managed group member (the [`MANAGED_PREFIX`] family) is ALREADY the KWin primary —
-/// desktop (KWin re-homes plasmashell + windows onto it). Returns the disabled outputs for the
+/// first-slot-wins support (§6.1) so a later exclusive session doesn't steal primary from the group's
-/// keepalive to re-enable on teardown. Best-effort: on failure, streaming continues (just possibly
+/// first member. Best-effort: if kscreen reports no primary flag we treat it as "none" (the session
+/// then sets itself primary — the pre-group behavior). Recent kscreen marks the primary with
+/// `"priority": 1`; older builds used a `"primary": true` bool — accept either.
+fn a_managed_output_is_primary() -> bool {
+    let Ok(out) = std::process::Command::new("kscreen-doctor").arg("-j").output() else {
+        return false;
+    };
+    let Ok(doc) = serde_json::from_slice::<serde_json::Value>(&out.stdout) else {
+        return false;
+    };
+    doc.get("outputs")
+        .and_then(|o| o.as_array())
+        .map(|outs| {
+            outs.iter().any(|o| {
+                let managed = o
+                    .get("name")
+                    .and_then(|n| n.as_str())
+                    .is_some_and(|n| n.starts_with(MANAGED_PREFIX));
+                let primary = o.get("primary").and_then(|p| p.as_bool()).unwrap_or(false)
+                    || o.get("priority").and_then(|p| p.as_u64()) == Some(1);
+                managed && primary
+            })
+        })
+        .unwrap_or(false)
+}
+
+/// Set `Virtual-punktfunk` primary and disable the bootstrap output(s) so the managed group becomes
+/// the sole desktop (KWin re-homes plasmashell + windows onto it). Returns the disabled outputs for
+/// the keepalive to re-enable on teardown. Best-effort: on failure, streaming continues (just possibly
 /// showing only the wallpaper) rather than failing the session.
-fn apply_virtual_primary() -> Vec<String> {
+fn apply_virtual_primary(name: &str) -> Vec<String> {
-    let ours = format!("Virtual-{VOUT_NAME}");
+    let ours = format!("Virtual-{name}");
     let kscreen = |args: &[String]| {
         std::process::Command::new("kscreen-doctor")
             .args(args)
@@ -271,15 +399,20 @@ fn apply_virtual_primary() -> Vec<String> {
             .map(|s| s.success())
             .unwrap_or(false)
     };
-    // Make ours primary — KWin usually then re-homes the desktop and disables the bootstrap on its
+    // First-slot-wins (§6.1): only grab primary if no managed group member is primary yet — so a 2nd
-    // own. Let that settle, then belt-and-suspenders: disable anything still enabled besides ours so
+    // exclusive session joins as a secondary monitor of the shared desktop instead of stealing the
-    // the streamed output is unambiguously the sole desktop regardless of KWin's implicit behaviour.
+    // shell off the 1st session's output. KWin usually then re-homes the desktop + disables the
-    if !kscreen(&[format!("output.{ours}.primary")]) {
+    // bootstrap on its own; the belt-and-suspenders disable below covers the rest.
-        tracing::warn!(
+    if !a_managed_output_is_primary() {
-            "KWin: could not set the virtual output primary; client may see only the wallpaper"
+        if !kscreen(&[format!("output.{ours}.primary")]) {
-        );
+            tracing::warn!(
+                "KWin: could not set the virtual output primary; client may see only the wallpaper"
+            );
+        }
+        std::thread::sleep(Duration::from_millis(200));
     }
-    std::thread::sleep(Duration::from_millis(200));
+    // Disable everything still enabled that ISN'T a managed group member (bootstrap / physical), so
+    // the group is unambiguously the desktop — never a sibling session's output (group-aware filter).
     let others = other_enabled_outputs();
     if !others.is_empty() {
         let args: Vec<String> = others
@@ -292,29 +425,33 @@ fn apply_virtual_primary() -> Vec<String> {
     others
 }
 
+/// **Primary** (Stage 2): make the streamed output the primary but KEEP the other outputs enabled
+/// (don't disable the bootstrap/physical) — so the shell re-homes onto the streamed surface while a
+/// physical screen stays usable. Nothing to restore on teardown (we disabled nothing).
+fn apply_virtual_primary_only(name: &str) {
+    let ours = format!("Virtual-{name}");
+    let ok = std::process::Command::new("kscreen-doctor")
+        .arg(format!("output.{ours}.primary"))
+        .status()
+        .map(|s| s.success())
+        .unwrap_or(false);
+    if ok {
+        tracing::info!("KWin: streamed output set primary (physical outputs kept)");
+    } else {
+        tracing::warn!("KWin: could not set the virtual output primary");
+    }
+}
+
 /// Dropping this releases the KWin virtual output: it flips the keepalive thread's `stop`, which
-/// drops the Wayland connection and makes KWin reclaim the output.
+/// drops the Wayland connection and makes KWin reclaim the output. The topology **restore** is no
+/// longer bound here — it moved to the registry's display group (§6.1, [`reenable_outputs`]), which
+/// runs it once when the group's last member drops, BEFORE this keepalive is dropped.
 struct StopGuard {
     stop: Arc<AtomicBool>,
-    /// Bootstrap output(s) `apply_virtual_primary` disabled to make our streamed output the sole
-    /// desktop — re-enabled here FIRST, so KWin is never left with zero enabled outputs as our
-    /// output is reclaimed. Empty unless PUNKTFUNK_KWIN_VIRTUAL_PRIMARY is set.
-    restore: Vec<String>,
 }
 
 impl Drop for StopGuard {
     fn drop(&mut self) {
-        if !self.restore.is_empty() {
-            let args: Vec<String> = self
-                .restore
-                .iter()
-                .map(|o| format!("output.{o}.enable"))
-                .collect();
-            let _ = std::process::Command::new("kscreen-doctor")
-                .args(&args)
-                .status();
-            std::thread::sleep(Duration::from_millis(200));
-        }
         self.stop.store(true, Ordering::Relaxed);
     }
 }
@@ -388,10 +525,11 @@ impl Dispatch<ScreencastStream, ()> for State {
 fn virtual_output_thread(
     width: u32,
     height: u32,
+    name: String,
     setup_tx: Sender<Result<u32, String>>,
     stop: Arc<AtomicBool>,
 ) {
-    if let Err(e) = run(width, height, &setup_tx, &stop) {
+    if let Err(e) = run(width, height, &name, &setup_tx, &stop) {
         // If we never delivered a node id, report the failure to the waiting opener.
         let _ = setup_tx.send(Err(format!("{e:#}")));
     }
@@ -431,6 +569,7 @@ pub fn is_available() -> bool {
 fn run(
     width: u32,
     height: u32,
+    name: &str,
     setup_tx: &Sender<Result<u32, String>>,
     stop: &AtomicBool,
 ) -> Result<()> {
@@ -453,7 +592,7 @@ fn run(
 
     // Create the virtual output sized to the client, cursor composited into the stream.
     let stream = screencast.stream_virtual_output(
-        VOUT_NAME.to_string(),
+        name.to_string(),
         width as i32,
         height as i32,
         1.0, // scale (logical == physical)
@@ -522,3 +661,27 @@ fn run(
     let _ = conn.flush();
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::MANAGED_PREFIX;
+
+    /// Group-aware exclusive (§6.1): with two managed group members + a physical panel enabled,
+    /// exclusive disables ONLY the non-managed panel — never a sibling session's per-slot output
+    /// (the Stage-3 naming would otherwise make a 2nd exclusive session black out the 1st).
+    #[test]
+    fn exclusive_disables_only_non_managed() {
+        let enabled = [
+            "Virtual-punktfunk",   // base name (shared identity)
+            "Virtual-punktfunk-1", // client A's per-slot output
+            "Virtual-punktfunk-7", // client B's per-slot output
+            "eDP-1",               // a physical panel
+        ];
+        let to_disable: Vec<&str> = enabled
+            .iter()
+            .copied()
+            .filter(|n| !n.starts_with(MANAGED_PREFIX))
+            .collect();
+        assert_eq!(to_disable, vec!["eDP-1"]);
+    }
+}

crates/punktfunk-host/src/vdisplay/linux/mutter.rs

@@ -42,11 +42,19 @@ const CURSOR_EMBEDDED: u32 = 1;
 
 /// The Mutter virtual-display driver. Each [`create`](VirtualDisplay::create) spins up a
 /// keepalive thread owning the D-Bus sessions behind the virtual monitor.
-pub struct MutterDisplay;
+pub struct MutterDisplay {
+    /// Whether this display is the FIRST of its group (§6.1) — set by the registry before `create`.
+    /// A later sibling **extends** into the already-exclusive desktop instead of re-applying the
+    /// sole-monitor config (which would disable the first session's virtual). Defaults true (a lone
+    /// session establishes topology as before).
+    first_in_group: bool,
+}
 
 impl MutterDisplay {
     pub fn new() -> Result<Self> {
-        Ok(MutterDisplay)
+        Ok(MutterDisplay {
+            first_in_group: true,
+        })
     }
 }
 
@@ -64,13 +72,18 @@ impl VirtualDisplay for MutterDisplay {
         "mutter"
     }
 
+    fn set_first_in_group(&mut self, first: bool) {
+        self.first_in_group = first;
+    }
+
     fn create(&mut self, mode: Mode) -> Result<VirtualOutput> {
         let (setup_tx, setup_rx) = std::sync::mpsc::channel::<Result<u32, String>>();
         let stop = Arc::new(AtomicBool::new(false));
         let stop_thread = stop.clone();
+        let first_in_group = self.first_in_group;
         thread::Builder::new()
             .name("punktfunk-mutter-vout".into())
-            .spawn(move || session_thread(setup_tx, stop_thread, mode))
+            .spawn(move || session_thread(setup_tx, stop_thread, mode, first_in_group))
             .context("spawn Mutter virtual-output thread")?;
 
         let node_id = match setup_rx.recv_timeout(Duration::from_secs(20)) {
@@ -104,8 +117,14 @@ impl Drop for StopGuard {
 }
 
 /// Keepalive thread: run the D-Bus handshake on a private tokio runtime, report the PipeWire
-/// node id, then hold the connection until stopped.
+/// node id, then hold the connection until stopped. `first_in_group` gates the topology change (a
-fn session_thread(setup_tx: Sender<Result<u32, String>>, stop: Arc<AtomicBool>, mode: Mode) {
+/// non-first sibling extends into the group's already-exclusive desktop instead of re-clobbering it).
+fn session_thread(
+    setup_tx: Sender<Result<u32, String>>,
+    stop: Arc<AtomicBool>,
+    mode: Mode,
+    first_in_group: bool,
+) {
     let rt = match tokio::runtime::Builder::new_multi_thread()
         .worker_threads(1)
         .enable_all()
@@ -118,9 +137,30 @@ fn session_thread(setup_tx: Sender<Result<u32, String>>, stop: Arc<AtomicBool>,
         }
     };
     rt.block_on(async move {
-        // Opt-in: snapshot the monitor layout BEFORE the virtual output exists, so we can tell the
+        // Display-management topology (Stage 2): the console policy's level, resolved to a concrete
-        // new (virtual) connector apart and restore the layout on teardown. Best-effort.
+        // value. `Extend` leaves the virtual output an extension (no config change); `Primary` makes
-        let dc_pre = if virtual_primary_enabled() {
+        // it the primary monitor but keeps the physicals as secondaries; `Exclusive` makes it the
+        // SOLE output (physicals disabled). `Auto` never reaches here — it's resolved upstream.
+        use crate::vdisplay::policy::Topology;
+        let topo = crate::vdisplay::effective_topology();
+        let topo_policy = matches!(topo, Topology::Primary | Topology::Exclusive);
+        // Group-aware (§6.1): only the FIRST display of the group establishes the topology. A later
+        // sibling extends into the already-exclusive desktop — re-applying the sole-monitor config would
+        // disable the first session's virtual output (Mutter connectors are un-nameable, so we can't
+        // build a config that keeps all group virtuals; skipping is the safe choice). *Concurrent
+        // Mutter exclusive is on-glass-validation-pending; the APPLY_TEMPORARY revert when the FIRST
+        // session leaves under a live sibling is a documented residual (design §7).*
+        let want_config = first_in_group && topo_policy;
+        if topo_policy && !first_in_group {
+            tracing::info!(
+                "mutter: joining an existing display group — extending (the first session owns the \
+                 exclusive/primary topology)"
+            );
+        }
+        let exclusive = matches!(topo, Topology::Exclusive);
+        // Snapshot the monitor layout BEFORE the virtual output exists (so we can tell the new
+        // connector apart and restore on teardown) whenever we're going to touch the topology.
+        let dc_pre = if want_config {
             match display_config().await {
                 Ok(dc) => match get_state(&dc).await {
                     Ok(state) => Some((dc, state)),
@@ -152,8 +192,12 @@ fn session_thread(setup_tx: Sender<Result<u32, String>>, stop: Arc<AtomicBool>,
         // monitor attached, the virtual output is an empty extended desktop — you stream only the
         // wallpaper. Best-effort: any failure just logs and streaming continues unchanged.
         if let Some((dc, pre)) = &dc_pre {
-            match make_virtual_primary(dc, mode, pre).await {
+            match make_virtual_primary(dc, mode, pre, exclusive).await {
-                Ok(()) => tracing::info!("mutter: virtual output set as the primary monitor"),
+                Ok(()) => tracing::info!(
+                    exclusive,
+                    "mutter: virtual output set as the primary monitor (physicals {})",
+                    if exclusive { "disabled" } else { "kept" }
+                ),
                 Err(e) => tracing::warn!(
                     "mutter: could not set the virtual output primary ({e:#}); streaming continues — the desktop may render on the physical monitor"
                 ),
@@ -338,17 +382,6 @@ type CurrentState = (
 type ApplyMon = (String, String, HashMap<String, Value<'static>>); // connector, mode_id, props
 type ApplyLogical = (i32, i32, f64, u32, bool, Vec<ApplyMon>);
 
-fn virtual_primary_enabled() -> bool {
-    std::env::var("PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY")
-        .map(|v| {
-            matches!(
-                v.trim().to_ascii_lowercase().as_str(),
-                "1" | "true" | "yes" | "on"
-            )
-        })
-        .unwrap_or(false)
-}
-
 /// Opt-in: pin the virtual output to the client's exact refresh via RecordVirtual "modes" (true
 /// above-60 Hz). Off by default — Mutter-derived 60 Hz is safe on every host; high-refresh virtual
 /// CRTCs are validated on Mutter 50 + NVIDIA but behaviour can vary, so it stays opt-in. (The
@@ -411,7 +444,12 @@ fn current_mode(state: &CurrentState, connector: &str) -> Option<(String, i32, i
 /// which lands shortly after the node id), then make it the SOLE primary output (physicals
 /// disabled for the session) so the cursor, windows, and keyboard focus stay on the streamed
 /// surface. Restored on teardown.
-async fn make_virtual_primary(dc: &zbus::Proxy<'_>, mode: Mode, pre: &CurrentState) -> Result<()> {
+async fn make_virtual_primary(
+    dc: &zbus::Proxy<'_>,
+    mode: Mode,
+    pre: &CurrentState,
+    exclusive: bool,
+) -> Result<()> {
     let pre_conns = connectors(pre);
     let deadline = Instant::now() + Duration::from_secs(6);
     loop {
@@ -437,7 +475,14 @@ async fn make_virtual_primary(dc: &zbus::Proxy<'_>, mode: Mode, pre: &CurrentSta
             let Some(vmode) = vmode else {
                 bail!("virtual monitor {vconn} has no usable mode yet");
             };
-            let config = build_primary_config(&vconn, &vmode);
+            // Exclusive: the virtual output alone (physicals omitted → Mutter disables them).
+            // Primary: the virtual output primary at (0,0) PLUS the physicals kept as secondaries.
+            // (On a headless host with no physicals the two are identical.)
+            let config = if exclusive {
+                build_exclusive_config(&vconn, &vmode)
+            } else {
+                build_primary_keeping_physicals(&state, &vconn, &vmode, mode.width as i32)
+            };
             let _: () = dc
                 .call(
                     "ApplyMonitorsConfig",
@@ -459,12 +504,12 @@ async fn make_virtual_primary(dc: &zbus::Proxy<'_>, mode: Mode, pre: &CurrentSta
     }
 }
 
-/// The virtual output as the SOLE, primary monitor — physical outputs are omitted, so Mutter
+/// **Exclusive** — the virtual output as the SOLE, primary monitor: physical outputs are omitted, so
-/// disables them for the session. This confines the cursor, windows, and keyboard focus to the
+/// Mutter disables them for the session. This confines the cursor, windows, and keyboard focus to the
 /// streamed surface; keeping the physical enabled as a *secondary* monitor instead lets relative
 /// pointer motion and window focus wander onto it (invisible to the client — the cursor seems to
 /// vanish). The physical layout is restored on teardown.
-fn build_primary_config(vconn: &str, vmode: &str) -> Vec<ApplyLogical> {
+fn build_exclusive_config(vconn: &str, vmode: &str) -> Vec<ApplyLogical> {
     vec![(
         0,
         0,
@@ -474,3 +519,47 @@ fn build_primary_config(vconn: &str, vmode: &str) -> Vec<ApplyLogical> {
         vec![(vconn.to_string(), vmode.to_string(), HashMap::new())],
     )]
 }
+
+/// **Primary** — the virtual output primary at `(0, 0)`, with every currently-active physical
+/// monitor KEPT as a secondary (laid left-to-right past the virtual, each at its current mode). So
+/// the shell + new windows land on the streamed surface, but the operator's physical screen stays
+/// on. On a headless host (no physicals) this is identical to [`build_exclusive_config`].
+///
+/// *Physical-keep is unvalidated on-glass* — the lab boxes are headless (no attached display to keep
+/// on); the layout math is conservative (append to the right) but wants a display-attached box.
+fn build_primary_keeping_physicals(
+    state: &CurrentState,
+    vconn: &str,
+    vmode: &str,
+    virt_width: i32,
+) -> Vec<ApplyLogical> {
+    let mut logicals: Vec<ApplyLogical> = vec![(
+        0,
+        0,
+        1.0,
+        0,
+        true,
+        vec![(vconn.to_string(), vmode.to_string(), HashMap::new())],
+    )];
+    // Append each physical (non-virtual) connector that has a usable current mode, to the right of
+    // the virtual output, as a non-primary secondary.
+    let mut x = virt_width.max(0);
+    for mon in &state.1 {
+        let conn = &mon.0 .0;
+        if conn == vconn {
+            continue;
+        }
+        if let Some((mode_id, w, _h)) = current_mode(state, conn) {
+            logicals.push((
+                x,
+                0,
+                1.0,
+                0,
+                false,
+                vec![(conn.clone(), mode_id, HashMap::new())],
+            ));
+            x += w.max(0);
+        }
+    }
+    logicals
+}

crates/punktfunk-host/src/vdisplay/policy.rs

@@ -0,0 +1,623 @@
+//! Virtual-display **management policy** — the user-configurable behavior surface for how virtual
+//! displays are created, kept alive, and arranged (design: `design/display-management.md`).
+//!
+//! This is the pure config layer that sits **above** the per-compositor [`VirtualDisplay`](super)
+//! backends: a small set of orthogonal options ([`DisplayPolicy`]) with safe defaults and named
+//! [`Preset`]s, persisted to `<config>/display-settings.json` and editable from the web console.
+//! The lifecycle/registry that *acts* on this policy lands in later stages; **Stage 0** (this file
+//! plus the mgmt endpoints) stands up the surface and wires the two behaviors the existing code can
+//! already express — the Windows monitor linger duration and the Linux "make the streamed output
+//! the sole desktop" topology — through it.
+//!
+//! Precedence, mirroring the GPU preference (`console preference > env pin > default`): a present,
+//! valid `display-settings.json` (console-written) **wins**; when it is absent the host keeps its
+//! historical env-knob / default behavior untouched ([`DisplayPolicyStore::configured`] returns
+//! `None`, and every Stage-0 call site falls back to exactly what it did before). The policy is
+//! read at each acquire/teardown (file state, not a startup-frozen env var), so a console change
+//! applies to the next connect without a host restart.
+//!
+//! The pure logic here — preset expansion, [`DisplayPolicy::effective`], the [`KeepAlive`] linger
+//! resolution — is unit-tested; the store adds file I/O around it (the `gpu.rs` discipline:
+//! private dir, temp-write + atomic rename, in-memory rollback on a failed write).
+
+use std::collections::BTreeMap;
+use std::path::PathBuf;
+use std::sync::{Mutex, OnceLock};
+use std::time::Duration;
+
+use anyhow::Result;
+use serde::{Deserialize, Serialize};
+use utoipa::ToSchema;
+
+/// How long a virtual display (and, on gamescope's bare spawn, the nested session + its game)
+/// survives after the last client session detaches. Serialized as an object tagged on `mode`
+/// (`{"mode":"off"}` / `{"mode":"duration","seconds":300}` / `{"mode":"forever"}`) so the web form
+/// and the OpenAPI schema stay simple.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize, ToSchema)]
+#[serde(tag = "mode", rename_all = "snake_case")]
+pub enum KeepAlive {
+    /// Tear the display down at session end (today's default on every backend but Windows, which
+    /// lingers 10 s).
+    Off,
+    /// Keep the display for `seconds` after the last session leaves, then tear it down; a reconnect
+    /// inside the window reuses it.
+    Duration {
+        /// Linger window in seconds.
+        seconds: u32,
+    },
+    /// Keep the display until host shutdown or an explicit release (the `Pinned` lifecycle state).
+    /// **Not honored until the display-lifecycle stage** — rejected by the mgmt PUT at Stage 0.
+    Forever,
+}
+
+impl Default for KeepAlive {
+    fn default() -> Self {
+        // The historical Windows behavior, made explicit; the Linux backends had no linger and map
+        // `Off`/short-duration onto their (nonexistent) keep-alive as a no-op until the lifecycle stage.
+        KeepAlive::Duration { seconds: 10 }
+    }
+}
+
+/// Resolved linger for the display lifecycle: teardown immediately, after a fixed window, or never.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Linger {
+    /// Tear down as soon as the last session leaves.
+    Immediate,
+    /// Linger for this window, then tear down.
+    For(Duration),
+    /// Never auto-tear-down (Pinned).
+    Forever,
+}
+
+impl KeepAlive {
+    /// The [`Linger`] this keep-alive resolves to.
+    pub fn linger(self) -> Linger {
+        match self {
+            KeepAlive::Off => Linger::Immediate,
+            KeepAlive::Duration { seconds } => Linger::For(Duration::from_secs(seconds as u64)),
+            KeepAlive::Forever => Linger::Forever,
+        }
+    }
+}
+
+/// What the host does to the box's display topology while managed virtual displays are up.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize, ToSchema)]
+#[serde(rename_all = "snake_case")]
+pub enum Topology {
+    /// Today's behavior, resolved per host at acquire time (see [`super::effective_topology`]):
+    /// exclusive on Windows and the auto-detected Linux desktop path, extend under an explicit
+    /// `PUNKTFUNK_COMPOSITOR` pin.
+    #[default]
+    Auto,
+    /// Add the virtual display(s); touch nothing else.
+    Extend,
+    /// Make the group's primary virtual display the OS primary; physical outputs stay enabled.
+    Primary,
+    /// The managed virtual displays become the only enabled outputs (physical outputs disabled,
+    /// restored on teardown).
+    Exclusive,
+}
+
+/// Admission when a *different* client connects while a display/session is already live and asks for
+/// a different mode. Stored at Stage 0; enforced from the mode-conflict admission stage.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize, ToSchema)]
+#[serde(rename_all = "snake_case")]
+pub enum ModeConflict {
+    /// Give the new client its own virtual display on the same desktop (today's Linux multi-view).
+    #[default]
+    Separate,
+    /// Stop the existing session(s), tear down / reconfigure, serve the new client.
+    Steal,
+    /// Admit the new client at the live display's mode (the honest-downgrade convention).
+    Join,
+    /// Refuse the new client with a clear handshake error.
+    Reject,
+}
+
+/// Stable display identity, so desktop environments persist per-display config (KDE scaling). Stored
+/// at Stage 0; carriers wired from the identity stage.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize, ToSchema)]
+#[serde(rename_all = "kebab-case")]
+pub enum Identity {
+    /// One identity for everything (today's Linux behavior).
+    Shared,
+    /// One identity per paired client cert fingerprint (today's Windows behavior).
+    #[default]
+    PerClient,
+    /// One identity per (client, resolution) — distinct scaling per resolution, at the cost of
+    /// identity slots.
+    PerClientMode,
+}
+
+/// How group members are arranged in the desktop coordinate space. Stored at Stage 0; applied from
+/// the multi-monitor stage.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize, ToSchema)]
+#[serde(rename_all = "kebab-case")]
+pub enum LayoutMode {
+    /// Left-to-right in acquire order, top-aligned (deterministic default).
+    #[default]
+    AutoRow,
+    /// Per-identity-slot offsets from [`Layout::positions`] (console-arranged).
+    Manual,
+}
+
+/// A desktop-space offset for a display (top-left origin).
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize, ToSchema)]
+pub struct Position {
+    pub x: i32,
+    pub y: i32,
+}
+
+/// Group layout: the arrangement mode plus, for [`LayoutMode::Manual`], per-slot offsets keyed by
+/// identity-slot id (string keys for stable JSON).
+#[derive(Clone, Debug, Default, PartialEq, Eq, Serialize, Deserialize, ToSchema)]
+pub struct Layout {
+    #[serde(default)]
+    pub mode: LayoutMode,
+    #[serde(default)]
+    pub positions: BTreeMap<String, Position>,
+}
+
+/// A named bundle of the fields below. `Custom` (the default) means the explicit fields rule; any
+/// other preset ignores the stored fields and expands to its own ([`DisplayPolicy::effective`]).
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize, ToSchema)]
+#[serde(rename_all = "kebab-case")]
+pub enum Preset {
+    /// The explicit fields below define the policy.
+    #[default]
+    Custom,
+    /// Today's behavior, made explicit.
+    Default,
+    /// Dedicated headless/couch box: displays + game survive disconnects; whoever connects takes over.
+    GamingRig,
+    /// A desktop someone also uses physically: never blank the real monitors, never keep ghosts.
+    SharedDesktop,
+    /// One user at a time with fast reattach; a second user is told the box is busy.
+    Hotdesk,
+    /// The multi-monitor daily driver: manual arrangement, per-client identity, exclusive.
+    Workstation,
+}
+
+/// The user-facing display-management policy — what `display-settings.json` holds and what the mgmt
+/// API GETs/PUTs. When [`preset`](Self::preset) is not [`Preset::Custom`] the explicit fields are
+/// ignored (the console writes one or the other); [`effective`](Self::effective) resolves both to a
+/// single [`EffectivePolicy`].
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize, ToSchema)]
+pub struct DisplayPolicy {
+    /// Schema version (currently 1) — lets a future field addition migrate rather than reject.
+    #[serde(default = "one")]
+    pub version: u32,
+    #[serde(default)]
+    pub preset: Preset,
+    #[serde(default)]
+    pub keep_alive: KeepAlive,
+    #[serde(default)]
+    pub topology: Topology,
+    #[serde(default)]
+    pub mode_conflict: ModeConflict,
+    #[serde(default)]
+    pub identity: Identity,
+    #[serde(default)]
+    pub layout: Layout,
+    /// Upper bound on simultaneously-live virtual displays (clamped to `1..=16` on write).
+    #[serde(default = "default_max_displays")]
+    pub max_displays: u32,
+}
+
+fn one() -> u32 {
+    1
+}
+fn default_max_displays() -> u32 {
+    4
+}
+
+impl Default for DisplayPolicy {
+    fn default() -> Self {
+        // Bit-for-bit today's behavior (the `default` preset expanded), so an unconfigured host reads
+        // the same policy the Stage-0 call sites already produce.
+        DisplayPolicy {
+            version: 1,
+            preset: Preset::Custom,
+            keep_alive: KeepAlive::default(),
+            topology: Topology::Auto,
+            mode_conflict: ModeConflict::default(),
+            identity: Identity::default(),
+            layout: Layout::default(),
+            max_displays: 4,
+        }
+    }
+}
+
+/// The six resolved fields after preset expansion — what the lifecycle/registry and the Stage-0 call
+/// sites read, and what the mgmt API echoes as the "currently in force" policy. Pure output of
+/// [`DisplayPolicy::effective`].
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize, ToSchema)]
+pub struct EffectivePolicy {
+    pub keep_alive: KeepAlive,
+    pub topology: Topology,
+    pub mode_conflict: ModeConflict,
+    pub identity: Identity,
+    pub layout: Layout,
+    pub max_displays: u32,
+}
+
+impl DisplayPolicy {
+    /// Resolve to the [`EffectivePolicy`]: a named preset expands to its bundle; `Custom` uses the
+    /// explicit fields. Pure — the single source of truth shared by the preset docs and the runtime.
+    pub fn effective(&self) -> EffectivePolicy {
+        if let Some(mut e) = preset_fields(self.preset) {
+            // A preset fixes the six behavior fields but honors an explicit manual layout table
+            // (positions are data, not behavior — the `workstation` preset only sets the *mode*).
+            if self.preset == Preset::Workstation && !self.layout.positions.is_empty() {
+                e.layout.positions = self.layout.positions.clone();
+            }
+            e
+        } else {
+            EffectivePolicy {
+                keep_alive: self.keep_alive,
+                topology: self.topology,
+                mode_conflict: self.mode_conflict,
+                identity: self.identity,
+                layout: self.layout.clone(),
+                max_displays: self.max_displays,
+            }
+        }
+    }
+
+    /// Clamp fields to their valid ranges (called on write). `max_displays` to `1..=16` (the
+    /// pf-vdisplay connector ceiling / a sane Linux bound).
+    pub fn sanitized(mut self) -> Self {
+        self.version = 1;
+        self.max_displays = self.max_displays.clamp(1, 16);
+        self
+    }
+}
+
+impl EffectivePolicy {
+    /// Build a persistable `Custom` [`DisplayPolicy`] that keeps THIS effective behavior but replaces
+    /// the arrangement with a **manual** layout at `positions` — the `/display/layout` endpoint's
+    /// transform, factored out pure so arranging displays stays orthogonal to the other axes and is
+    /// unit-tested without touching the global store. (`Custom` so the explicit fields — incl. the new
+    /// layout — rule; a named preset would ignore them.)
+    pub fn with_manual_layout(&self, positions: BTreeMap<String, Position>) -> DisplayPolicy {
+        DisplayPolicy {
+            version: 1,
+            preset: Preset::Custom,
+            keep_alive: self.keep_alive,
+            topology: self.topology,
+            mode_conflict: self.mode_conflict,
+            identity: self.identity,
+            layout: Layout {
+                mode: LayoutMode::Manual,
+                positions,
+            },
+            max_displays: self.max_displays,
+        }
+    }
+}
+
+/// The field bundle a named preset expands to; `None` for [`Preset::Custom`]. The single expansion
+/// table — the docs' preset table mirrors this and the `presets_match_doc` test guards the shape.
+pub fn preset_fields(preset: Preset) -> Option<EffectivePolicy> {
+    let base = |keep_alive, topology, mode_conflict, identity, layout_mode| EffectivePolicy {
+        keep_alive,
+        topology,
+        mode_conflict,
+        identity,
+        layout: Layout {
+            mode: layout_mode,
+            positions: BTreeMap::new(),
+        },
+        max_displays: 4,
+    };
+    Some(match preset {
+        Preset::Custom => return None,
+        Preset::Default => base(
+            KeepAlive::Duration { seconds: 10 },
+            Topology::Auto,
+            ModeConflict::Separate,
+            Identity::PerClient,
+            LayoutMode::AutoRow,
+        ),
+        Preset::GamingRig => base(
+            KeepAlive::Forever,
+            Topology::Exclusive,
+            ModeConflict::Steal,
+            Identity::PerClient,
+            LayoutMode::AutoRow,
+        ),
+        Preset::SharedDesktop => base(
+            KeepAlive::Off,
+            Topology::Extend,
+            ModeConflict::Separate,
+            Identity::PerClient,
+            LayoutMode::AutoRow,
+        ),
+        Preset::Hotdesk => base(
+            KeepAlive::Duration { seconds: 300 },
+            Topology::Exclusive,
+            ModeConflict::Reject,
+            Identity::PerClientMode,
+            LayoutMode::AutoRow,
+        ),
+        Preset::Workstation => base(
+            KeepAlive::Duration { seconds: 300 },
+            Topology::Exclusive,
+            ModeConflict::Separate,
+            Identity::PerClient,
+            LayoutMode::Manual,
+        ),
+    })
+}
+
+/// The persisted policy store: the loaded file value (or `None` when no file exists) behind its
+/// JSON path. Mirrors [`crate::gpu::GpuPrefStore`] — private dir, temp-write + atomic rename,
+/// in-memory rollback if the disk write fails.
+pub struct DisplayPolicyStore {
+    path: PathBuf,
+    /// `Some` only when a valid `display-settings.json` was loaded / written — the "console has
+    /// configured this host" signal that gates whether Stage-0 call sites override their historical
+    /// env/default behavior.
+    cur: Mutex<Option<DisplayPolicy>>,
+}
+
+impl DisplayPolicyStore {
+    /// Load from `path`. A missing file ⇒ unconfigured (`None`); a corrupt file ⇒ unconfigured with a
+    /// warning (never fail host startup over a settings file).
+    pub fn load_from(path: PathBuf) -> Self {
+        let cur = match std::fs::read(&path) {
+            Ok(bytes) => match serde_json::from_slice::<DisplayPolicy>(&bytes) {
+                Ok(p) => Some(p),
+                Err(e) => {
+                    tracing::warn!(path = %path.display(),
+                        "display-settings.json unreadable — using built-in defaults: {e}");
+                    None
+                }
+            },
+            Err(_) => None,
+        };
+        DisplayPolicyStore {
+            path,
+            cur: Mutex::new(cur),
+        }
+    }
+
+    /// The stored policy, or [`DisplayPolicy::default`] when unconfigured (for the mgmt GET).
+    pub fn get(&self) -> DisplayPolicy {
+        self.cur.lock().unwrap().clone().unwrap_or_default()
+    }
+
+    /// The console-configured policy, or `None` when no settings file exists. Stage-0 call sites use
+    /// this to decide whether to override their historical behavior (`None` ⇒ leave it untouched).
+    pub fn configured(&self) -> Option<DisplayPolicy> {
+        self.cur.lock().unwrap().clone()
+    }
+
+    /// The effective (preset-expanded) policy the console configured, or `None` when unconfigured.
+    pub fn configured_effective(&self) -> Option<EffectivePolicy> {
+        self.configured().map(|p| p.effective())
+    }
+
+    /// Persist + adopt a new policy (sanitized first). The in-memory value changes only if the disk
+    /// write succeeds, so a full disk can't leave memory and file disagreeing.
+    pub fn set(&self, policy: DisplayPolicy) -> Result<()> {
+        let policy = policy.sanitized();
+        if let Some(dir) = self.path.parent() {
+            crate::gamestream::create_private_dir(dir)?;
+        }
+        let tmp = self.path.with_extension("json.tmp");
+        crate::gamestream::write_secret_file(&tmp, &serde_json::to_vec_pretty(&policy)?)?;
+        std::fs::rename(&tmp, &self.path)?;
+        *self.cur.lock().unwrap() = Some(policy);
+        Ok(())
+    }
+}
+
+/// The process-wide display-policy store (config-dir file), loaded once on first access — the same
+/// global-accessor shape as [`crate::gpu::prefs`], because display setup happens deep in the
+/// capture/vdisplay path where no app state is threaded.
+pub fn prefs() -> &'static DisplayPolicyStore {
+    static STORE: OnceLock<DisplayPolicyStore> = OnceLock::new();
+    STORE.get_or_init(|| {
+        DisplayPolicyStore::load_from(crate::gamestream::config_dir().join("display-settings.json"))
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn keep_alive_serializes_tagged_on_mode() {
+        assert_eq!(
+            serde_json::to_value(KeepAlive::Duration { seconds: 300 }).unwrap(),
+            serde_json::json!({ "mode": "duration", "seconds": 300 })
+        );
+        assert_eq!(
+            serde_json::to_value(KeepAlive::Off).unwrap(),
+            serde_json::json!({ "mode": "off" })
+        );
+        assert_eq!(
+            serde_json::to_value(KeepAlive::Forever).unwrap(),
+            serde_json::json!({ "mode": "forever" })
+        );
+        // Round-trips.
+        for k in [
+            KeepAlive::Off,
+            KeepAlive::Duration { seconds: 42 },
+            KeepAlive::Forever,
+        ] {
+            let s = serde_json::to_string(&k).unwrap();
+            assert_eq!(serde_json::from_str::<KeepAlive>(&s).unwrap(), k);
+        }
+    }
+
+    #[test]
+    fn keep_alive_linger_resolution() {
+        assert_eq!(KeepAlive::Off.linger(), Linger::Immediate);
+        assert_eq!(
+            KeepAlive::Duration { seconds: 30 }.linger(),
+            Linger::For(Duration::from_secs(30))
+        );
+        assert_eq!(KeepAlive::Forever.linger(), Linger::Forever);
+    }
+
+    #[test]
+    fn default_policy_is_todays_behavior() {
+        let e = DisplayPolicy::default().effective();
+        assert_eq!(e.keep_alive, KeepAlive::Duration { seconds: 10 });
+        assert_eq!(e.topology, Topology::Auto);
+        assert_eq!(e.mode_conflict, ModeConflict::Separate);
+        assert_eq!(e.identity, Identity::PerClient);
+        assert_eq!(e.layout.mode, LayoutMode::AutoRow);
+    }
+
+    #[test]
+    fn custom_uses_explicit_fields_presets_override_them() {
+        // Custom: explicit fields flow through.
+        let p = DisplayPolicy {
+            preset: Preset::Custom,
+            keep_alive: KeepAlive::Off,
+            topology: Topology::Extend,
+            ..DisplayPolicy::default()
+        };
+        assert_eq!(p.effective().keep_alive, KeepAlive::Off);
+        assert_eq!(p.effective().topology, Topology::Extend);
+
+        // A named preset ignores the explicit fields.
+        let p = DisplayPolicy {
+            preset: Preset::GamingRig,
+            keep_alive: KeepAlive::Off, // ignored
+            topology: Topology::Extend, // ignored
+            ..DisplayPolicy::default()
+        };
+        let e = p.effective();
+        assert_eq!(e.keep_alive, KeepAlive::Forever);
+        assert_eq!(e.topology, Topology::Exclusive);
+        assert_eq!(e.mode_conflict, ModeConflict::Steal);
+    }
+
+    #[test]
+    fn workstation_preset_keeps_manual_layout_positions() {
+        let mut positions = BTreeMap::new();
+        positions.insert("1".to_string(), Position { x: 2560, y: 0 });
+        let p = DisplayPolicy {
+            preset: Preset::Workstation,
+            layout: Layout {
+                mode: LayoutMode::AutoRow, // preset forces Manual regardless
+                positions,
+            },
+            ..DisplayPolicy::default()
+        };
+        let e = p.effective();
+        assert_eq!(e.layout.mode, LayoutMode::Manual);
+        assert_eq!(
+            e.layout.positions.get("1"),
+            Some(&Position { x: 2560, y: 0 })
+        );
+    }
+
+    #[test]
+    fn every_preset_expands() {
+        for preset in [
+            Preset::Default,
+            Preset::GamingRig,
+            Preset::SharedDesktop,
+            Preset::Hotdesk,
+            Preset::Workstation,
+        ] {
+            assert!(preset_fields(preset).is_some(), "{preset:?} must expand");
+        }
+        assert!(preset_fields(Preset::Custom).is_none());
+    }
+
+    #[test]
+    fn sanitize_clamps_max_displays_and_pins_version() {
+        let p = DisplayPolicy {
+            version: 99,
+            max_displays: 0,
+            ..DisplayPolicy::default()
+        }
+        .sanitized();
+        assert_eq!(p.version, 1);
+        assert_eq!(p.max_displays, 1);
+        let p = DisplayPolicy {
+            max_displays: 999,
+            ..DisplayPolicy::default()
+        }
+        .sanitized();
+        assert_eq!(p.max_displays, 16);
+    }
+
+    #[test]
+    fn with_manual_layout_preserves_behavior_and_sets_positions() {
+        // Start from a preset's effective behavior (workstation: 5-min linger, exclusive, per-client).
+        let eff = DisplayPolicy {
+            preset: Preset::Workstation,
+            ..DisplayPolicy::default()
+        }
+        .effective();
+        let mut positions = BTreeMap::new();
+        positions.insert("1".to_string(), Position { x: 0, y: 0 });
+        positions.insert("7".to_string(), Position { x: 2560, y: 0 });
+        let p = eff.with_manual_layout(positions);
+        // Preset drops to Custom so the explicit fields (incl. the layout) rule…
+        assert_eq!(p.preset, Preset::Custom);
+        // …every other behavior axis is preserved verbatim…
+        assert_eq!(p.keep_alive, eff.keep_alive);
+        assert_eq!(p.topology, eff.topology);
+        assert_eq!(p.mode_conflict, eff.mode_conflict);
+        assert_eq!(p.identity, eff.identity);
+        assert_eq!(p.max_displays, eff.max_displays);
+        // …and the arrangement is the manual layout we asked for, surviving the effective round-trip.
+        let e2 = p.effective();
+        assert_eq!(e2.layout.mode, LayoutMode::Manual);
+        let want = Position { x: 2560, y: 0 };
+        assert_eq!(e2.layout.positions.get("7"), Some(&want));
+    }
+
+    #[test]
+    fn partial_json_fills_defaults() {
+        // A hand-written file with only a couple of fields loads, the rest defaulting.
+        let p: DisplayPolicy =
+            serde_json::from_str(r#"{ "preset": "custom", "max_displays": 2 }"#).unwrap();
+        assert_eq!(p.max_displays, 2);
+        assert_eq!(p.keep_alive, KeepAlive::default());
+        assert_eq!(p.topology, Topology::Auto);
+        assert_eq!(p.version, 1);
+    }
+
+    #[test]
+    fn store_roundtrips_and_gates_on_file_presence() {
+        let dir = std::env::temp_dir().join(format!("pf-disp-{}", std::process::id()));
+        let _ = std::fs::create_dir_all(&dir);
+        let path = dir.join("display-settings.json");
+        let _ = std::fs::remove_file(&path);
+
+        let store = DisplayPolicyStore::load_from(path.clone());
+        // Unconfigured: get() yields defaults, configured() is None.
+        assert!(store.configured().is_none());
+        assert_eq!(store.get(), DisplayPolicy::default());
+
+        // After a write the file gates flip to configured.
+        let want = DisplayPolicy {
+            preset: Preset::SharedDesktop,
+            ..DisplayPolicy::default()
+        };
+        store.set(want.clone()).unwrap();
+        assert_eq!(
+            store.configured().as_ref().map(|p| p.preset),
+            Some(Preset::SharedDesktop)
+        );
+        assert_eq!(
+            store.configured_effective().unwrap().keep_alive,
+            KeepAlive::Off
+        );
+
+        // A fresh store reading the same path sees the persisted value.
+        let reopened = DisplayPolicyStore::load_from(path.clone());
+        assert_eq!(reopened.configured().unwrap().preset, Preset::SharedDesktop);
+
+        let _ = std::fs::remove_file(&path);
+    }
+}

crates/punktfunk-host/src/vdisplay/registry.rs

@@ -0,0 +1,940 @@
+//! Host-lifetime **virtual-display registry** (design: `design/display-management.md` §3/§7): the
+//! owner of the display lifecycle, so a display can outlive the session that created it (keep-alive)
+//! and the management API can list + release kept displays.
+//!
+//! **Windows** already owns its lifecycle in [`super::manager::VirtualDisplayManager`] (one shared
+//! IddCx monitor, refcounted, lingering); [`acquire`] there is a pass-through to `vd.create` (the
+//! manager does the leasing), and [`snapshot`]/[`release`] read/control it.
+//!
+//! **Linux** gains a per-session **pool** here, driven by the pure [`super::lifecycle`] machine. The
+//! key enabling fact: KWin / Mutter / gamescope put their capture node on the *default* PipeWire
+//! daemon (`VirtualOutput::remote_fd == None`), reachable by `node_id` alone — so keeping the
+//! backend's keepalive alive keeps the node alive, and a reconnect just re-attaches a fresh PipeWire
+//! consumer to the same `node_id`. No fd dup / re-open needed. wlroots (`remote_fd == Some`, the
+//! sandboxed xdpw portal) can't be kept without re-opening the portal fd per attach, so it is passed
+//! through unchanged (teardown-on-drop, today's behavior) until that fresh-portal-capture re-attach
+//! lands — a runtime gate on `remote_fd.is_some()`.
+//!
+//! The ownership split: the session's capturer no longer owns the real keepalive — the registry does.
+//! [`acquire`] hands the session a `VirtualOutput` whose `keepalive` is a lightweight, gen-stamped
+//! `DisplayLease` (mirrors the Windows `MonitorLease`); dropping it releases the registry refcount,
+//! and the lifecycle machine decides linger / teardown. `capture_virtual_output`'s signature is
+//! unchanged — it just holds a lease instead of the real keepalive.
+
+use anyhow::Result;
+
+/// One live or kept virtual display, for the mgmt snapshot.
+#[derive(Clone, Debug)]
+pub struct DisplayInfo {
+    /// A stable-enough id for the `/display/release` slot argument (the owner's generation stamp).
+    pub slot: u64,
+    /// Backend name (`"pf-vdisplay"`, `"kwin"`, `"mutter"`, …).
+    pub backend: String,
+    /// `(width, height, refresh_hz)`.
+    pub mode: (u32, u32, u32),
+    /// `"active"` | `"lingering"` | `"pinned"`.
+    pub state: String,
+    /// Milliseconds until a lingering display is torn down (`None` when active/pinned).
+    pub expires_in_ms: Option<u64>,
+    /// Live sessions holding the display.
+    pub sessions: u32,
+    /// Short client label (cert-fp prefix / peer), when the owner tracks it.
+    pub client: Option<String>,
+    /// Display **group** (shared desktop) id (design §6.1): Linux gives every backend session one
+    /// group; Windows is single-group (`1`).
+    pub group: u32,
+    /// This display's ordinal within its group, in acquire order (0-based) — the §6A "which monitor".
+    pub display_index: u32,
+    /// Desktop-space top-left origin `(x, y)` (design §6.2): auto-row, or the console's manual
+    /// arrangement when configured.
+    pub position: (i32, i32),
+    /// The stable per-client identity slot keying this display's persistent config + manual layout
+    /// (§5.4); `None` for a shared/anonymous identity.
+    pub identity_slot: Option<u32>,
+    /// The effective topology for this display's group (`"extend"` | `"primary"` | `"exclusive"`).
+    pub topology: String,
+}
+
+/// The live display set for the mgmt `/display/state` endpoint.
+#[derive(Clone, Debug, Default)]
+pub struct Snapshot {
+    pub displays: Vec<DisplayInfo>,
+}
+
+/// The effective display topology as a lowercase string for the snapshot (`effective_topology`
+/// resolves `Auto` away; the arm is defensive).
+fn topology_str() -> String {
+    use super::policy::Topology;
+    match super::effective_topology() {
+        Topology::Extend => "extend",
+        Topology::Primary => "primary",
+        Topology::Exclusive => "exclusive",
+        Topology::Auto => "auto",
+    }
+    .to_string()
+}
+
+/// Acquire a virtual display for a session: reuse a kept (lingering/pinned) display of the same
+/// backend + mode if one exists, else create a fresh one. Returns a [`VirtualOutput`](super::VirtualOutput)
+/// the capturer consumes as before — but its `keepalive` is a registry lease, so the *display*
+/// outlives the capturer per the keep-alive policy.
+///
+/// Windows delegates to the [`manager`](super::manager) via `vd.create` (unchanged); Linux uses the
+/// pool below; other platforms pass through.
+/// `quit` is the session's deliberate-quit flag: when the session ends with it set (the client closed
+/// with the quit application code — a user "stop", not a network drop), the display is torn down
+/// **immediately**, skipping the keep-alive linger. A bare disconnect leaves it `false` → normal linger.
+pub fn acquire(
+    vd: &mut Box<dyn super::VirtualDisplay>,
+    mode: super::Mode,
+    quit: std::sync::Arc<std::sync::atomic::AtomicBool>,
+) -> Result<super::VirtualOutput> {
+    #[cfg(target_os = "linux")]
+    {
+        linux::acquire(vd, mode, quit)
+    }
+    #[cfg(not(target_os = "linux"))]
+    {
+        // Windows leases in the manager (its own linger); the deliberate-quit skip is not wired
+        // through there yet, so the flag is accepted but unused off Linux.
+        let _ = quit;
+        vd.create(mode)
+    }
+}
+
+/// Snapshot the host's managed virtual displays. Cheap + side-effect-free (a state-lock read);
+/// safe per management request.
+pub fn snapshot() -> Snapshot {
+    #[cfg(target_os = "windows")]
+    {
+        // Windows is single-monitor at this stage (§6.6 multi-monitor is Stage 7): one group, index 0,
+        // origin. Its per-client identity lives in the driver (EDID serial / ConnectorIndex), not
+        // surfaced here yet.
+        let displays = super::manager::snapshot()
+            .map(|i| DisplayInfo {
+                slot: i.gen,
+                backend: i.backend.to_string(),
+                mode: i.mode,
+                state: i.state.to_string(),
+                expires_in_ms: i.expires_in_ms,
+                sessions: i.sessions,
+                client: None,
+                group: 1,
+                display_index: 0,
+                position: (0, 0),
+                identity_slot: None,
+                topology: topology_str(),
+            })
+            .into_iter()
+            .collect();
+        Snapshot { displays }
+    }
+    #[cfg(target_os = "linux")]
+    {
+        Snapshot {
+            displays: linux::snapshot(),
+        }
+    }
+    #[cfg(not(any(target_os = "windows", target_os = "linux")))]
+    {
+        Snapshot::default()
+    }
+}
+
+/// Force-release kept (lingering/pinned) displays now — the `/display/release` endpoint. `slot`
+/// selects one by [`DisplayInfo::slot`]; `None` releases every kept display. Active displays are
+/// refused (releasing a display with live sessions is session management). Returns the number
+/// released.
+pub fn release(slot: Option<u64>) -> usize {
+    #[cfg(target_os = "windows")]
+    {
+        // Windows manages a single shared monitor at Stage 1, so `slot` is moot — release the one
+        // lingering monitor if present. (Multi-monitor gives `slot` meaning later.)
+        let _ = slot;
+        usize::from(super::manager::force_release())
+    }
+    #[cfg(target_os = "linux")]
+    {
+        linux::force_release(slot)
+    }
+    #[cfg(not(any(target_os = "windows", target_os = "linux")))]
+    {
+        let _ = slot;
+        0
+    }
+}
+
+// ---------------------------------------------------------------------------------------------
+// Linux keep-alive pool
+// ---------------------------------------------------------------------------------------------
+
+#[cfg(target_os = "linux")]
+mod linux {
+    use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
+    use std::sync::{Arc, Mutex, Once, OnceLock};
+    use std::time::{Duration, Instant};
+
+    use anyhow::Result;
+
+    use super::DisplayInfo;
+    use crate::vdisplay::lifecycle::{self, Release};
+    use crate::vdisplay::policy::{self, Layout, Linger};
+    use crate::vdisplay::{Mode, VirtualDisplay, VirtualOutput};
+
+    /// One pooled display: the lifecycle state + the backend's REAL keepalive (kept alive here so the
+    /// compositor output — and thus its PipeWire `node_id` — survives past the session), plus the
+    /// capture coordinates a reconnecting session needs.
+    struct Entry {
+        life: lifecycle::State,
+        /// The backend's keepalive (KWin Wayland conn / Mutter D-Bus session / gamescope child). Its
+        /// `Drop` releases the compositor output — so it is dropped only on teardown/expiry.
+        keepalive: Box<dyn Send>,
+        node_id: u32,
+        preferred_mode: Option<(u32, u32, u32)>,
+        mode: Mode,
+        backend: &'static str,
+        /// The identity slot the backend resolved for this display (KWin per-slot naming; `None` for
+        /// shared/anonymous or a backend with no per-client identity) — keys the group arrangement +
+        /// the `/display/state` slot. Captured at create; kept across a keep-alive reuse.
+        identity_slot: Option<u32>,
+        /// The topology-restore action for this display's GROUP (design §6.1): re-enable the physical
+        /// outputs an `exclusive` topology disabled. At most ONE entry per group carries it (the first
+        /// exclusive session); on teardown it hands off to a surviving sibling, and only runs when the
+        /// group's last member drops. `None` for extend/primary and non-first / non-exclusive members.
+        topology_restore: Option<Restore>,
+        /// Generation stamp: a [`DisplayLease`] only releases if its gen still matches (a stale lease
+        /// — its entry was reused + re-stamped — is a no-op).
+        gen: u64,
+    }
+
+    /// A per-group topology-restore action (see [`Entry::topology_restore`]).
+    type Restore = Box<dyn FnOnce() + Send>;
+
+    /// Hand off a torn-down display's topology restore (design §6.1 — per-group restore): if a
+    /// same-group (backend) sibling survives in `remaining`, MOVE the restore onto it (a later teardown
+    /// runs it); if the group is now empty, RETURN the action so the caller runs it (before dropping the
+    /// reclaimed display's keepalive, so the physical is re-enabled while our output still exists —
+    /// the compositor never sees zero outputs). `None` in → `None` out.
+    fn hand_off_restore(
+        remaining: &mut [Entry],
+        backend: &'static str,
+        restore: Option<Restore>,
+    ) -> Option<Restore> {
+        let action = restore?;
+        // At most one restore per group, so any surviving sibling has `None` to receive it.
+        match remaining.iter_mut().find(|e| e.backend == backend) {
+            Some(sibling) => {
+                sibling.topology_restore = Some(action);
+                None
+            }
+            None => Some(action), // group empty → run it now
+        }
+    }
+
+    struct Reg {
+        entries: Mutex<Vec<Entry>>,
+        gen: AtomicU64,
+    }
+
+    static REG: OnceLock<Reg> = OnceLock::new();
+
+    fn reg() -> &'static Reg {
+        REG.get_or_init(|| Reg {
+            entries: Mutex::new(Vec::new()),
+            gen: AtomicU64::new(1),
+        })
+    }
+
+    /// The linger resolution for Linux: the console policy's `keep_alive` when configured, else
+    /// **Immediate** (today's behavior — a Linux disconnect tears the output down at once).
+    fn linger() -> Linger {
+        policy::prefs()
+            .configured_effective()
+            .map(|e| e.keep_alive.linger())
+            .unwrap_or(Linger::Immediate)
+    }
+
+    /// Remove entries whose linger deadline has passed, returning them so the caller drops (tears
+    /// them down) *after* releasing the lock — a backend keepalive `Drop` (Mutter D-Bus Stop) can
+    /// block, and holding the pool lock across it would stall every other acquire/release. Each
+    /// expired entry's topology restore is [handed off](hand_off_restore) to a surviving group sibling,
+    /// or collected into the returned `restores` when its group empties (run before the entries drop).
+    fn take_expired(entries: &mut Vec<Entry>, now: Instant) -> (Vec<Entry>, Vec<Restore>) {
+        let mut expired = Vec::new();
+        let mut restores = Vec::new();
+        let mut i = 0;
+        while i < entries.len() {
+            if entries[i].life.poll_expiry(now) {
+                let mut e = entries.remove(i);
+                let backend = e.backend;
+                if let Some(r) = hand_off_restore(entries, backend, e.topology_restore.take()) {
+                    restores.push(r);
+                }
+                expired.push(e);
+            } else {
+                i += 1;
+            }
+        }
+        (expired, restores)
+    }
+
+    /// Background thread (started once): reap lingering displays past their deadline.
+    fn ensure_timer() {
+        static ONCE: Once = Once::new();
+        ONCE.call_once(|| {
+            let _ = std::thread::Builder::new()
+                .name("vdisplay-linger".into())
+                .spawn(|| loop {
+                    std::thread::sleep(Duration::from_millis(500));
+                    let (expired, restores) = {
+                        let mut es = reg().entries.lock().unwrap();
+                        take_expired(&mut es, Instant::now())
+                    };
+                    // Re-enable physicals (group emptied) BEFORE dropping the outputs — outside the lock.
+                    for restore in restores {
+                        restore();
+                    }
+                    for e in expired {
+                        tracing::info!(
+                            backend = e.backend,
+                            "virtual display: linger expired — torn down"
+                        );
+                        drop(e); // outside the lock
+                    }
+                });
+        });
+    }
+
+    /// Build the session-facing [`VirtualOutput`]: the kept node + a fresh gen-stamped lease. Only
+    /// the poolable (`remote_fd == None`) backends reach here, so `remote_fd` is always `None`.
+    fn output_for(
+        node_id: u32,
+        preferred_mode: Option<(u32, u32, u32)>,
+        gen: u64,
+        quit: Arc<AtomicBool>,
+    ) -> VirtualOutput {
+        VirtualOutput {
+            node_id,
+            remote_fd: None,
+            preferred_mode,
+            keepalive: Box::new(DisplayLease { gen, quit }),
+        }
+    }
+
+    pub(super) fn acquire(
+        vd: &mut Box<dyn VirtualDisplay>,
+        mode: Mode,
+        quit: Arc<AtomicBool>,
+    ) -> Result<VirtualOutput> {
+        ensure_timer();
+        let backend = vd.name();
+        let r = reg();
+
+        // Reap expired first (run any group restores + drop outside the lock).
+        let (expired, restores) = {
+            let mut es = r.entries.lock().unwrap();
+            take_expired(&mut es, Instant::now())
+        };
+        for restore in restores {
+            restore();
+        }
+        drop(expired);
+
+        // Reuse: a kept (lingering/pinned) display of the same backend + mode. A reconnecting session
+        // re-attaches a fresh PipeWire consumer to the still-live `node_id`.
+        {
+            let mut es = r.entries.lock().unwrap();
+            if let Some(e) = es.iter_mut().find(|e| {
+                matches!(
+                    e.life,
+                    lifecycle::State::Lingering { .. } | lifecycle::State::Pinned
+                ) && e.backend == backend
+                    && e.mode == mode
+            }) {
+                // Lingering/Pinned → Active (Acquire::Reuse); side effect matters, value is known.
+                e.life.acquire();
+                let gen = r.gen.fetch_add(1, Ordering::Relaxed);
+                e.gen = gen;
+                let out = output_for(e.node_id, e.preferred_mode, gen, quit);
+                tracing::info!(
+                    backend,
+                    node_id = e.node_id,
+                    "virtual display reused (keep-alive reconnect)"
+                );
+                return Ok(out);
+            }
+        }
+
+        // Tell the backend whether it's the FIRST display of its group (no same-backend sibling live,
+        // §6.1) — so a topology-establishing backend (Mutter exclusive) extends into an already-exclusive
+        // desktop rather than re-clobbering the first session's virtual. Best-effort (a concurrent create
+        // is a narrow race); single-session is always `first == true` → today's behavior.
+        let first_in_group = {
+            let es = r.entries.lock().unwrap();
+            !es.iter().any(|e| e.backend == backend)
+        };
+        vd.set_first_in_group(first_in_group);
+
+        // Create a fresh display (NOT under the lock — `vd.create` blocks + spawns threads).
+        let real = vd.create(mode)?;
+        // The identity slot the backend just resolved (KWin per-slot naming; `None` elsewhere) — keys
+        // the group arrangement (manual per-slot positions) + the state slot.
+        let identity_slot = vd.last_identity_slot();
+
+        // wlroots (remote_fd = Some, sandboxed xdpw portal) can't be kept without re-opening the
+        // portal fd per attach — pass it through unchanged (capturer owns it, teardown on drop). The
+        // poolable backends put their node on the default daemon (remote_fd = None).
+        if real.remote_fd.is_some() {
+            tracing::debug!(
+                backend,
+                "virtual display not poolable (portal fd) — keep-alive off for this backend"
+            );
+            return Ok(real);
+        }
+
+        let node_id = real.node_id;
+        let preferred_mode = real.preferred_mode;
+        // The backend's topology-restore action (KWin `exclusive` → re-enable the disabled physicals),
+        // lifted into the group so it runs once when the group's last member drops (§6.1), not at this
+        // session's teardown. `None` for non-exclusive / non-first / backends whose topology auto-reverts.
+        let topology_restore = vd.take_topology_restore();
+        let gen = r.gen.fetch_add(1, Ordering::Relaxed);
+        let mut life = lifecycle::State::default();
+        life.acquire(); // Idle → Active{refs:1} (Acquire::Create)
+        let entry = Entry {
+            life,
+            keepalive: real.keepalive,
+            node_id,
+            preferred_mode,
+            mode,
+            backend,
+            identity_slot,
+            topology_restore,
+            gen,
+        };
+
+        // Compute this new display's position in its group (design §6.2) BEFORE pushing, then push
+        // under the same lock: the group is the same-backend entries; the new one appends last
+        // (rightmost under auto-row). `position_for_new` is pure; the lock is held only across it
+        // (I/O-free) — the backend apply is below, outside the lock.
+        let position = {
+            use crate::vdisplay::layout::Member;
+            let layout_policy = policy::prefs()
+                .configured_effective()
+                .map(|e| e.layout)
+                .unwrap_or_default();
+            let mut es = r.entries.lock().unwrap();
+            // Same-group members (design §6.1): same backend for a shared desktop, but each gamescope
+            // spawn is its own group, so a new gamescope never auto-rows against another.
+            let new_group = group_key(backend, gen);
+            let existing: Vec<(u64, Member)> = es
+                .iter()
+                .filter(|e| group_key(e.backend, e.gen) == new_group)
+                .map(|e| {
+                    (
+                        e.gen,
+                        Member {
+                            identity_slot: e.identity_slot,
+                            width: e.mode.width as i32,
+                        },
+                    )
+                })
+                .collect();
+            let new_member = Member {
+                identity_slot,
+                width: mode.width as i32,
+            };
+            let pos = position_for_new(existing, new_member, &layout_policy);
+            es.push(entry);
+            pos
+        };
+        // Place the new output (design §6.2), best-effort, OUTSIDE the lock (kscreen blocks). Skip the
+        // desktop origin `(0, 0)` — it's the compositor default, so a single-display / first-of-group
+        // session (and every non-KWin backend, which no-ops `apply_position`) issues no positioning at
+        // all: the historical single-display path is untouched. *On-glass-validation-pending.*
+        if (position.x, position.y) != (0, 0) {
+            vd.apply_position(position.x, position.y);
+        }
+        Ok(output_for(node_id, preferred_mode, gen, quit))
+    }
+
+    /// The [`DisplayLease`] `Drop` path: release the session's hold on the pooled display. The
+    /// lifecycle machine decides linger / pin / teardown; a torn-down entry's keepalive drops *after*
+    /// the lock is released.
+    fn release(gen: u64, force_immediate: bool) {
+        let Some(r) = REG.get() else { return };
+        // A deliberate quit (the client closed with the quit code — a user "stop") tears the display
+        // down NOW, overriding the keep-alive linger; a bare disconnect honors the policy.
+        let linger = if force_immediate {
+            Linger::Immediate
+        } else {
+            linger()
+        };
+        let (torn_down, restore) = {
+            let mut es = r.entries.lock().unwrap();
+            let Some(idx) = es.iter().position(|e| e.gen == gen) else {
+                return; // stale lease (entry reused + re-stamped, or already gone) — no-op
+            };
+            match es[idx].life.release(Instant::now(), linger) {
+                Release::Teardown | Release::Noop => {
+                    let mut e = es.remove(idx);
+                    let backend = e.backend;
+                    // Per-group restore (§6.1): hand the physical re-enable to a surviving sibling, or run
+                    // it now if this was the group's last member.
+                    let restore = hand_off_restore(&mut es, backend, e.topology_restore.take());
+                    (Some(e), restore)
+                }
+                Release::Linger => {
+                    tracing::info!(
+                        backend = es[idx].backend,
+                        "virtual display: last session left — lingering (keep-alive)"
+                    );
+                    (None, None)
+                }
+                Release::Pin => {
+                    tracing::info!(
+                        backend = es[idx].backend,
+                        "virtual display: last session left — pinned (keep-alive forever)"
+                    );
+                    (None, None)
+                }
+                // Linux entries are single-session (refs == 1), so Decref never occurs; harmless.
+                Release::Decref => (None, None),
+            }
+        };
+        // Re-enable the physicals (group emptied) BEFORE dropping the output — outside the lock.
+        if let Some(restore) = restore {
+            restore();
+        }
+        if let Some(e) = torn_down {
+            if force_immediate {
+                tracing::info!(
+                    backend = e.backend,
+                    "virtual display torn down (deliberate quit — keep-alive skipped)"
+                );
+            } else {
+                tracing::info!(
+                    backend = e.backend,
+                    "virtual display torn down (keep-alive off / released)"
+                );
+            }
+            drop(e); // outside the lock — the keepalive Drop may block
+        }
+    }
+
+    /// One live/kept display, flattened out of the pool under the lock — so the group + arrangement
+    /// math (which calls the layout engine) runs OUTSIDE the lock.
+    struct Row {
+        gen: u64,
+        backend: &'static str,
+        mode: Mode,
+        identity_slot: Option<u32>,
+        state: &'static str,
+        expires_in_ms: Option<u64>,
+        sessions: u32,
+    }
+
+    pub(super) fn snapshot() -> Vec<DisplayInfo> {
+        let Some(r) = REG.get() else {
+            return Vec::new();
+        };
+        let now = Instant::now();
+
+        // Flatten the live/kept entries under the lock (skip Idle — never stored anyway).
+        let rows: Vec<Row> = {
+            let es = r.entries.lock().unwrap();
+            es.iter()
+                .filter_map(|e| {
+                    let (state, expires_in_ms, sessions) = match e.life {
+                        lifecycle::State::Active { refs } => ("active", None, refs),
+                        lifecycle::State::Lingering { until } => (
+                            "lingering",
+                            Some(until.saturating_duration_since(now).as_millis() as u64),
+                            0,
+                        ),
+                        lifecycle::State::Pinned => ("pinned", None, 0),
+                        lifecycle::State::Idle => return None,
+                    };
+                    Some(Row {
+                        gen: e.gen,
+                        backend: e.backend,
+                        mode: e.mode,
+                        identity_slot: e.identity_slot,
+                        state,
+                        expires_in_ms,
+                        sessions,
+                    })
+                })
+                .collect()
+        };
+
+        let topology = super::topology_str();
+        // The arrangement policy: the console's manual layout when configured, else auto-row.
+        let layout_policy: Layout = policy::prefs()
+            .configured_effective()
+            .map(|e| e.layout)
+            .unwrap_or_default();
+
+        assemble_displays(rows, &layout_policy, &topology)
+    }
+
+    /// The desktop position for a display just appended to its group (design §6.2): the group's
+    /// `existing` members (each with its acquire `gen`) plus `new` last, ordered by `gen`, arranged by
+    /// the pure [`layout`] engine, taking the new member's placement. Pure — so the append-in-acquire-
+    /// order + auto-row/manual arrangement is unit-tested independent of the pool/global.
+    fn position_for_new(
+        mut existing: Vec<(u64, crate::vdisplay::layout::Member)>,
+        new: crate::vdisplay::layout::Member,
+        layout_policy: &Layout,
+    ) -> crate::vdisplay::layout::Placement {
+        existing.sort_by_key(|(g, _)| *g);
+        let mut members: Vec<crate::vdisplay::layout::Member> =
+            existing.into_iter().map(|(_, m)| m).collect();
+        members.push(new);
+        *crate::vdisplay::layout::arrange(&members, layout_policy)
+            .last()
+            .expect("members is non-empty (just pushed `new`)")
+    }
+
+    /// The display **group** a backend+display belongs to (design §6.1). The desktop compositors
+    /// (KWin/Mutter/wlroots) put every managed output on ONE desktop → one group per backend. A
+    /// gamescope **spawn** is an independent nested session per client (no shared desktop), so each
+    /// gamescope display is its OWN group — never auto-rowed against, or topology-/restore-grouped with,
+    /// another gamescope session.
+    fn group_key(backend: &str, gen: u64) -> String {
+        if backend == "gamescope" {
+            format!("gamescope#{gen}")
+        } else {
+            backend.to_string()
+        }
+    }
+
+    /// Group the flattened rows into the mgmt `/display/state` view (design §6.1/§6.2) by
+    /// [`group_key`], ordered by acquire (`gen`), with each member's position from the pure [`layout`]
+    /// engine. Pure — no I/O, no global — so the grouping / ordering / position assignment is
+    /// unit-tested against synthetic rows.
+    fn assemble_displays(
+        rows: Vec<Row>,
+        layout_policy: &Layout,
+        topology: &str,
+    ) -> Vec<DisplayInfo> {
+        use crate::vdisplay::layout::{self, Member};
+
+        // Small stable group ids by sorted group key — deterministic; in practice a host runs one live
+        // desktop backend → group 1 (with each gamescope spawn its own group).
+        let mut keys: Vec<String> = rows.iter().map(|r| group_key(r.backend, r.gen)).collect();
+        keys.sort();
+        keys.dedup();
+
+        let mut out: Vec<DisplayInfo> = Vec::new();
+        for (gi, key) in keys.iter().enumerate() {
+            // This group's members in acquire order (gen ascending) → display_index + arrangement.
+            let mut idx: Vec<usize> = rows
+                .iter()
+                .enumerate()
+                .filter(|(_, row)| &group_key(row.backend, row.gen) == key)
+                .map(|(i, _)| i)
+                .collect();
+            idx.sort_by_key(|&i| rows[i].gen);
+            let members: Vec<Member> = idx
+                .iter()
+                .map(|&i| Member {
+                    identity_slot: rows[i].identity_slot,
+                    width: rows[i].mode.width as i32,
+                })
+                .collect();
+            let places = layout::arrange(&members, layout_policy);
+            for (ord, &i) in idx.iter().enumerate() {
+                let row = &rows[i];
+                let p = places[ord];
+                out.push(DisplayInfo {
+                    slot: row.gen,
+                    backend: row.backend.to_string(),
+                    mode: (row.mode.width, row.mode.height, row.mode.refresh_hz),
+                    state: row.state.to_string(),
+                    expires_in_ms: row.expires_in_ms,
+                    sessions: row.sessions,
+                    client: None,
+                    group: gi as u32 + 1,
+                    display_index: ord as u32,
+                    position: (p.x, p.y),
+                    identity_slot: row.identity_slot,
+                    topology: topology.to_string(),
+                });
+            }
+        }
+        out
+    }
+
+    pub(super) fn force_release(slot: Option<u64>) -> usize {
+        let Some(r) = REG.get() else { return 0 };
+        let (released, restores) = {
+            let mut es = r.entries.lock().unwrap();
+            let mut out = Vec::new();
+            let mut restores = Vec::new();
+            let mut i = 0;
+            while i < es.len() {
+                let selected = slot.is_none_or(|s| es[i].gen == s);
+                if selected && es[i].life.force_release() {
+                    let mut e = es.remove(i);
+                    let backend = e.backend;
+                    let restore = e.topology_restore.take();
+                    if let Some(rst) = hand_off_restore(&mut es, backend, restore) {
+                        restores.push(rst);
+                    }
+                    out.push(e);
+                } else {
+                    i += 1;
+                }
+            }
+            (out, restores)
+        };
+        let n = released.len();
+        // Re-enable physicals (group emptied) BEFORE dropping the outputs — outside the lock.
+        for restore in restores {
+            restore();
+        }
+        for e in released {
+            tracing::info!(
+                backend = e.backend,
+                "virtual display released (mgmt /display/release)"
+            );
+            drop(e);
+        }
+        n
+    }
+
+    /// The session's refcount handle — the `keepalive` the capturer holds. `Drop` releases the
+    /// registry hold; a stale lease (its entry was reused + re-stamped, or torn down) is a no-op.
+    struct DisplayLease {
+        gen: u64,
+        /// The session's deliberate-quit flag: set when the client closes with the quit application
+        /// code (a user "stop", not a network drop), so this lease's `Drop` tears the display down
+        /// immediately instead of lingering. `false` on a bare disconnect → normal keep-alive.
+        quit: Arc<AtomicBool>,
+    }
+
+    impl Drop for DisplayLease {
+        fn drop(&mut self) {
+            release(self.gen, self.quit.load(Ordering::SeqCst));
+        }
+    }
+
+    #[cfg(test)]
+    mod tests {
+        use super::*;
+        use crate::vdisplay::policy::{Layout, LayoutMode, Position};
+        use std::collections::BTreeMap;
+        use std::sync::atomic::{AtomicBool, Ordering};
+        use std::sync::Arc;
+
+        /// A minimal pool entry for the pure teardown/restore tests (dummy keepalive; the
+        /// `hand_off_restore` logic only reads `backend` + `topology_restore`).
+        fn test_entry(backend: &'static str, gen: u64, restore: Option<Restore>) -> Entry {
+            Entry {
+                life: lifecycle::State::default(),
+                keepalive: Box::new(()),
+                node_id: 0,
+                preferred_mode: None,
+                mode: Mode {
+                    width: 1920,
+                    height: 1080,
+                    refresh_hz: 60,
+                },
+                backend,
+                identity_slot: None,
+                topology_restore: restore,
+                gen,
+            }
+        }
+
+        /// A restore closure that flips `flag` when run — so a test can assert exactly WHEN it fires.
+        fn flag_restore(flag: &Arc<AtomicBool>) -> Restore {
+            let f = flag.clone();
+            Box::new(move || f.store(true, Ordering::SeqCst))
+        }
+
+        #[test]
+        fn topology_restore_floats_to_a_sibling_then_runs_on_the_last_teardown() {
+            let ran = Arc::new(AtomicBool::new(false));
+            // Two KWin displays in one group; the first (gen 1) carries the group's restore.
+            let mut pool = vec![
+                test_entry("kwin", 1, Some(flag_restore(&ran))),
+                test_entry("kwin", 2, None),
+            ];
+
+            // Tear down the restore-carrier while its sibling is still alive → transfer, don't run.
+            let mut e1 = pool.remove(0);
+            let out = hand_off_restore(&mut pool, "kwin", e1.topology_restore.take());
+            assert!(out.is_none(), "transferred, not run");
+            assert!(!ran.load(Ordering::SeqCst));
+            // The restore floated onto the surviving sibling.
+            assert!(pool[0].topology_restore.is_some());
+
+            // Tear down the last member → group empty → the restore is returned to run.
+            let mut e2 = pool.remove(0);
+            let out = hand_off_restore(&mut pool, "kwin", e2.topology_restore.take());
+            let action = out.expect("group empty → run the restore");
+            assert!(!ran.load(Ordering::SeqCst), "not run yet");
+            action();
+            assert!(ran.load(Ordering::SeqCst), "runs on the last drop");
+        }
+
+        #[test]
+        fn single_session_topology_restore_runs_on_its_own_teardown() {
+            // The validated single-display case: one exclusive session → restore runs at its teardown.
+            let ran = Arc::new(AtomicBool::new(false));
+            let mut pool = vec![test_entry("kwin", 1, Some(flag_restore(&ran)))];
+            let mut e = pool.remove(0);
+            let action = hand_off_restore(&mut pool, "kwin", e.topology_restore.take())
+                .expect("last (only) member → run");
+            action();
+            assert!(ran.load(Ordering::SeqCst));
+        }
+
+        #[test]
+        fn tearing_down_a_non_carrier_first_leaves_the_restore_for_last() {
+            let ran = Arc::new(AtomicBool::new(false));
+            // gen 2 carries the restore; gen 1 does not (a later exclusive session found the physical
+            // already disabled).
+            let mut pool = vec![
+                test_entry("kwin", 1, None),
+                test_entry("kwin", 2, Some(flag_restore(&ran))),
+            ];
+            // Tear down the non-carrier first → nothing to hand off, carrier untouched.
+            let mut e1 = pool.remove(0);
+            assert!(hand_off_restore(&mut pool, "kwin", e1.topology_restore.take()).is_none());
+            // The carrier (gen 2) still holds the group's restore.
+            assert!(pool[0].topology_restore.is_some());
+            // Now the carrier (last member) → run.
+            let mut e2 = pool.remove(0);
+            hand_off_restore(&mut pool, "kwin", e2.topology_restore.take())
+                .expect("last member → run")();
+            assert!(ran.load(Ordering::SeqCst));
+        }
+
+        #[test]
+        fn restore_never_floats_across_backends() {
+            // group = backend: a KWin restore must not land on a Mutter display (a different desktop).
+            let ran = Arc::new(AtomicBool::new(false));
+            let mut pool = vec![test_entry("mutter", 2, None)];
+            let out = hand_off_restore(&mut pool, "kwin", Some(flag_restore(&ran)));
+            assert!(out.is_some(), "no same-backend sibling → return to run");
+            assert!(
+                pool[0].topology_restore.is_none(),
+                "restore must not cross into another backend's group"
+            );
+        }
+
+        fn row(gen: u64, backend: &'static str, w: u32, slot: Option<u32>) -> Row {
+            Row {
+                gen,
+                backend,
+                mode: Mode {
+                    width: w,
+                    height: 1080,
+                    refresh_hz: 60,
+                },
+                identity_slot: slot,
+                state: "active",
+                expires_in_ms: None,
+                sessions: 1,
+            }
+        }
+
+        #[test]
+        fn groups_by_backend_and_auto_rows_in_acquire_order() {
+            // Two KWin displays (acquired gen 5 then gen 2 — deliberately out of vec order) + a Mutter one.
+            let rows = vec![
+                row(5, "kwin", 2560, Some(1)),
+                row(2, "kwin", 1920, Some(7)),
+                row(9, "mutter", 3840, None),
+            ];
+            let out = assemble_displays(rows, &Layout::default(), "exclusive");
+
+            let kwin: Vec<&DisplayInfo> = out.iter().filter(|d| d.backend == "kwin").collect();
+            assert_eq!(kwin.len(), 2);
+            assert_eq!(kwin[0].slot, 2); // lower gen (earlier acquire) sorts to index 0
+            assert_eq!(kwin[0].display_index, 0);
+            assert_eq!(kwin[0].position, (0, 0));
+            assert_eq!(kwin[1].slot, 5);
+            assert_eq!(kwin[1].display_index, 1);
+            assert_eq!(kwin[1].position, (1920, 0)); // auto-row: after the 1920px gen-2 display
+            assert_eq!(kwin[0].topology, "exclusive");
+
+            // A distinct backend is a distinct group.
+            let mutter = out.iter().find(|d| d.backend == "mutter").unwrap();
+            assert_ne!(mutter.group, kwin[0].group);
+            assert_eq!(mutter.display_index, 0);
+            assert_eq!(mutter.position, (0, 0));
+        }
+
+        #[test]
+        fn position_for_new_appends_right_in_acquire_order() {
+            use crate::vdisplay::layout::{Member, Placement};
+            let m = |slot, w| Member {
+                identity_slot: slot,
+                width: w,
+            };
+            // Existing group (given out of gen order): gen 8 @ 1920 acquired AFTER gen 3 @ 2560.
+            let existing = vec![(8, m(Some(2), 1920)), (3, m(Some(1), 2560))];
+            // A new 1280-wide display appends to the right of 2560 + 1920.
+            let pos = position_for_new(existing, m(Some(5), 1280), &Layout::default());
+            assert_eq!(pos, Placement { x: 4480, y: 0 });
+            // First-of-group lands at the origin (so the registry skips the apply).
+            let first = position_for_new(vec![], m(None, 3840), &Layout::default());
+            assert_eq!(first, Placement { x: 0, y: 0 });
+        }
+
+        #[test]
+        fn position_for_new_honors_a_manual_pin() {
+            use crate::vdisplay::layout::{Member, Placement};
+            let mut positions = BTreeMap::new();
+            positions.insert("5".to_string(), Position { x: 100, y: 200 });
+            let layout = Layout {
+                mode: LayoutMode::Manual,
+                positions,
+            };
+            let new = Member {
+                identity_slot: Some(5),
+                width: 1280,
+            };
+            let pos = position_for_new(vec![(1, new)], new, &layout);
+            assert_eq!(pos, Placement { x: 100, y: 200 });
+        }
+
+        #[test]
+        fn gamescope_spawns_are_separate_groups() {
+            // Two independent gamescope spawns must NOT share a group or auto-row against each other.
+            let rows = vec![
+                row(1, "gamescope", 1920, None),
+                row(2, "gamescope", 1280, None),
+            ];
+            let out = assemble_displays(rows, &Layout::default(), "extend");
+            assert_eq!(out.len(), 2);
+            assert_ne!(out[0].group, out[1].group, "distinct groups");
+            // Each is display 0 of its own group, at the origin (not auto-rowed against the other).
+            assert_eq!(out[0].display_index, 0);
+            assert_eq!(out[1].display_index, 0);
+            assert_eq!(out[0].position, (0, 0));
+            assert_eq!(out[1].position, (0, 0));
+        }
+
+        #[test]
+        fn manual_layout_keys_positions_by_identity_slot() {
+            // Client 7 arranged to the LEFT of client 1 (reversed vs. auto-row).
+            let rows = vec![row(1, "kwin", 2560, Some(1)), row(2, "kwin", 1920, Some(7))];
+            let mut positions = BTreeMap::new();
+            positions.insert("1".to_string(), Position { x: 1920, y: 0 });
+            positions.insert("7".to_string(), Position { x: 0, y: 0 });
+            let layout = Layout {
+                mode: LayoutMode::Manual,
+                positions,
+            };
+            let out = assemble_displays(rows, &layout, "extend");
+            let by_slot = |s: u32| out.iter().find(|d| d.identity_slot == Some(s)).unwrap();
+            assert_eq!(by_slot(1).position, (1920, 0));
+            assert_eq!(by_slot(7).position, (0, 0));
+        }
+    }
+}

crates/punktfunk-host/src/vdisplay/windows/identity.rs

@@ -1,172 +0,0 @@
-//! Per-client → stable monitor-id map for pf-vdisplay (Phase 2: per-client display-config persistence).
-//!
-//! Windows keys per-monitor config — notably DPI **scaling** (`HKCU\Control Panel\Desktop\PerMonitorSettings`)
-//! — on the monitor's EDID identity AND its OS device path (whose per-connector discriminator is the IddCx
-//! `ConnectorIndex` → target UID). The pf-vdisplay driver seeds BOTH the EDID serial and the `ConnectorIndex`
-//! from a single monitor `id`. So for Windows to REAPPLY a given client's saved scaling on reconnect, that
-//! client must get the SAME `id` every time. This map assigns each client (keyed by its cert fingerprint) a
-//! STABLE id and the host passes it as [`AddRequest::preferred_monitor_id`](pf_driver_proto::control::AddRequest).
-//!
-//! The id space is bounded to `1..=15` because the driver uses the id as the IddCx `ConnectorIndex`, which
-//! must stay `< MaxMonitorsSupported` (16). When more than 15 distinct clients are remembered, the
-//! LEAST-RECENTLY-USED entry is evicted and its id reused (that evicted client simply re-establishes its
-//! scaling once on its next connect). The map persists to `%ProgramData%\punktfunk\pf-vdisplay-identity.json`
-//! so ids — and therefore the client→config association — survive host restarts.
-//!
-//! Anonymous/TOFU and GameStream sessions have no fingerprint and resolve to id `0` (auto) upstream, never
-//! reaching this map — they keep the driver's lowest-free slot behavior unchanged.
-
-use std::path::PathBuf;
-
-use serde::{Deserialize, Serialize};
-
-/// Max stable id. The driver uses the id as the IddCx `ConnectorIndex`, which must stay
-/// `< MaxMonitorsSupported` (16) — so ids run `1..=15`.
-const MAX_ID: u32 = 15;
-
-#[derive(Serialize, Deserialize, Default)]
-struct Store {
-    /// Monotonic most-recently-used counter (the entry with the highest `seen` is the MRU). Persisted so
-    /// the LRU ordering survives host restarts.
-    tick: u64,
-    entries: Vec<Entry>,
-}
-
-#[derive(Serialize, Deserialize)]
-struct Entry {
-    /// Lower-hex client cert fingerprint (the map key).
-    fp: String,
-    /// The client's stable monitor id (`1..=15`).
-    id: u32,
-    /// MRU stamp (compared against [`Store::tick`]).
-    seen: u64,
-}
-
-/// Persistent fingerprint → stable-id map (see the module docs).
-pub(crate) struct MonitorIdentityMap {
-    path: PathBuf,
-    store: Store,
-}
-
-impl MonitorIdentityMap {
-    /// Load the persisted map (empty on first run / unreadable / parse failure — a fresh map just
-    /// re-derives ids, costing a client one scaling re-set the first time).
-    pub(crate) fn load() -> Self {
-        let path = crate::gamestream::config_dir().join("pf-vdisplay-identity.json");
-        let mut store = std::fs::read(&path)
-            .ok()
-            .and_then(|b| serde_json::from_slice::<Store>(&b).ok())
-            .unwrap_or_default();
-        // SANITIZE a hand-edited / corrupt / cross-version file before trusting it: resolve()'s found-entry
-        // branch returns the stored id verbatim, so an out-of-range id (0 = the "auto" sentinel, or
-        // > MAX_ID) or a duplicate id/fp would flow straight into preferred_monitor_id. Drop out-of-range
-        // ids and dedup by BOTH fp and id (keeping the most-recently-seen on a clash) so no two fingerprints
-        // can map to the same id. (The driver also rejects a live-colliding id as a backstop.)
-        store.entries.sort_by_key(|e| std::cmp::Reverse(e.seen));
-        let mut seen_fp = std::collections::HashSet::new();
-        let mut seen_id = std::collections::HashSet::new();
-        store.entries.retain(|e| {
-            (1..=MAX_ID).contains(&e.id) && seen_fp.insert(e.fp.clone()) && seen_id.insert(e.id)
-        });
-        Self { path, store }
-    }
-
-    /// The stable id (`1..=15`) for the client fingerprint `fp`: its remembered id, or a freshly assigned
-    /// one (lowest free, else LRU-evict at the cap). Bumps the entry to MRU and persists.
-    pub(crate) fn resolve(&mut self, fp: [u8; 32]) -> u32 {
-        let key: String = fp.iter().map(|b| format!("{b:02x}")).collect();
-        self.store.tick = self.store.tick.wrapping_add(1);
-        let now = self.store.tick;
-
-        if let Some(e) = self.store.entries.iter_mut().find(|e| e.fp == key) {
-            e.seen = now;
-            let id = e.id;
-            self.persist();
-            return id;
-        }
-
-        // New client: prefer the lowest free id in 1..=MAX_ID; if all are taken, evict the LRU entry and
-        // reuse its id (the evicted client re-establishes its scaling once on its next connect).
-        let id = (1..=MAX_ID)
-            .find(|i| !self.store.entries.iter().any(|e| e.id == *i))
-            .unwrap_or_else(|| {
-                let lru = self
-                    .store
-                    .entries
-                    .iter()
-                    .enumerate()
-                    .min_by_key(|(_, e)| e.seen)
-                    .map(|(i, _)| i)
-                    .expect("entries are non-empty whenever every id 1..=MAX_ID is taken");
-                let evicted = self.store.entries.remove(lru);
-                evicted.id
-            });
-        self.store.entries.push(Entry {
-            fp: key,
-            id,
-            seen: now,
-        });
-        self.persist();
-        id
-    }
-
-    /// Persist atomically (temp file + rename). Best-effort: a write failure just means a restart may
-    /// re-derive an id (one scaling re-set). Not a credential, so a plain (non-ACL'd) write is fine.
-    fn persist(&self) {
-        let Ok(bytes) = serde_json::to_vec_pretty(&self.store) else {
-            return;
-        };
-        if let Some(dir) = self.path.parent() {
-            let _ = std::fs::create_dir_all(dir);
-        }
-        let tmp = self.path.with_extension("json.tmp");
-        if std::fs::write(&tmp, &bytes).is_ok() {
-            let _ = std::fs::rename(&tmp, &self.path);
-        }
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    fn fp(n: u8) -> [u8; 32] {
-        let mut f = [0u8; 32];
-        f[0] = n;
-        f
-    }
-
-    #[test]
-    fn stable_across_calls_and_distinct_per_client() {
-        let mut m = MonitorIdentityMap {
-            path: std::env::temp_dir().join(format!("pf-id-test-{}.json", std::process::id())),
-            store: Store::default(),
-        };
-        let a1 = m.resolve(fp(1));
-        let b = m.resolve(fp(2));
-        let a2 = m.resolve(fp(1));
-        assert_eq!(a1, a2, "same client → same id");
-        assert_ne!(a1, b, "distinct clients → distinct ids");
-        assert!((1..=MAX_ID).contains(&a1) && (1..=MAX_ID).contains(&b));
-        let _ = std::fs::remove_file(&m.path);
-    }
-
-    #[test]
-    fn lru_eviction_reuses_an_id_at_the_cap() {
-        let mut m = MonitorIdentityMap {
-            path: std::env::temp_dir().join(format!("pf-id-lru-{}.json", std::process::id())),
-            store: Store::default(),
-        };
-        // Fill all 15 ids (clients 1..=15), then touch client 2 so client 1 is the LRU.
-        for n in 1..=15u8 {
-            m.resolve(fp(n));
-        }
-        let _ = m.resolve(fp(2));
-        // A 16th client evicts the LRU (client 1) and reuses its id; ids stay bounded.
-        let id16 = m.resolve(fp(16));
-        assert!((1..=MAX_ID).contains(&id16));
-        assert_eq!(m.store.entries.len(), 15, "cap holds at 15 entries");
-        assert!(m.store.entries.iter().all(|e| (1..=MAX_ID).contains(&e.id)));
-        let _ = std::fs::remove_file(&m.path);
-    }
-}

crates/punktfunk-host/src/vdisplay/windows/manager.rs

@@ -34,7 +34,7 @@ use windows::Win32::System::Threading::{
 use super::{Mode, VirtualOutput};
 use crate::win_display::{
     force_extend_topology, isolate_displays_ccd, resolve_gdi_name, restore_displays_ccd,
-    set_active_mode, SavedConfig,
+    set_active_mode, set_virtual_primary_ccd, SavedConfig,
 };
 
 /// The per-backend REMOVE key the driver stamps on ADD and consumes on REMOVE. SudoVDA keys monitors by
@@ -131,6 +131,12 @@ enum MgrState {
     Idle,
     Active { mon: Monitor, refs: u32 },
     Lingering { mon: Monitor, until: Instant },
+    /// `keep_alive = forever` (gaming-rig): the monitor is kept indefinitely after the last session
+    /// leaves — like `Lingering` but the linger timer never tears it down. A reconnect preempts +
+    /// recreates it (same as `Lingering`, since a reused IddCx swap-chain is dead); only the mgmt
+    /// `/display/release` (or host shutdown) frees it. The physical screens stay off (exclusive) for
+    /// the box's life — the §8 release-now escape hatch (`force_release`) is the way back.
+    Pinned { mon: Monitor },
 }
 
 /// The manager's control-device cache. Reopenable: a driver upgrade / WUDFHost restart kills the
@@ -169,10 +175,10 @@ pub(crate) struct VirtualDisplayManager {
     /// The current IDD-push session's stop flag; a new connection signals the prior one to release its
     /// monitor before the fresh one is created (was the `IDD_SESSION_STOP` global in `punktfunk1`).
     idd_session_stop: Mutex<Option<Arc<AtomicBool>>>,
-    /// Persistent per-client (cert-fingerprint) → stable monitor-id map. A monitor CREATE resolves the
+    // The per-client stable monitor-id map is now the process-wide `super::identity::global()`
-    /// connecting client's id here, so the client keeps the same EDID serial + IddCx ConnectorIndex across
+    // (shared with the Linux KWin backend's per-slot naming — never same-process). A monitor CREATE
-    /// reconnects and Windows reapplies its saved per-monitor config (DPI scaling). See [`super::identity`].
+    // resolves the client's id via `identity::resolve_slot`, so it keeps the same EDID serial + IddCx
-    identity_map: Mutex<super::identity::MonitorIdentityMap>,
+    // ConnectorIndex across reconnects and Windows reapplies its saved per-monitor DPI scaling.
 }
 
 static VDM: OnceLock<VirtualDisplayManager> = OnceLock::new();
@@ -188,7 +194,6 @@ pub(crate) fn init(driver: Box<dyn VdisplayDriver>) -> &'static VirtualDisplayMa
         state: Mutex::new(MgrState::Idle),
         setup_lock: Mutex::new(()),
         idd_session_stop: Mutex::new(None),
-        identity_map: Mutex::new(super::identity::MonitorIdentityMap::load()),
     })
 }
 
@@ -387,22 +392,28 @@ impl VirtualDisplayManager {
         let mut state = self.state.lock().unwrap();
         let dev = self.ensure_device()?;
 
-        // IDD-push: a new connection while a monitor is LINGERING is a single-client RECONNECT (the
+        // IDD-push: a new connection while a monitor is kept (LINGERING or PINNED) is a single-client
-        // prior session fully released). A REUSED IddCx swap-chain is DEAD, so reusing it hands a black
+        // RECONNECT (the prior session fully released). A REUSED IddCx swap-chain is DEAD, so reusing it
-        // screen — PREEMPT: tear the lingering monitor down (its key/topology are restored) and create a
+        // hands a black screen — PREEMPT: tear the kept monitor down (its key/topology are restored) and
-        // fresh one. The old session's lease is gen-stamped, so its later drop is a no-op.
+        // create a fresh one. The old session's lease is gen-stamped, so its later drop is a no-op.
         //
-        // ONLY Lingering, NOT Active: an Active monitor still has a lease held — that's the build-retry
+        // ONLY the kept states, NOT Active: an Active monitor still has a lease held — that's the
-        // path (`build_pipeline_with_retry` holds one lease across all attempts) or a concurrent session,
+        // build-retry path (`build_pipeline_with_retry` holds one lease across all attempts) or a
-        // NOT a reconnect. Preempting Active would tear a live session down AND churn REMOVE→ADD on every
+        // concurrent session, NOT a reconnect. Preempting Active would tear a live session down AND churn
-        // retry — the per-cold-start monitor churn that exhausts the IddCx slot pool and wedges ADD at
+        // REMOVE→ADD on every retry — the per-cold-start monitor churn that exhausts the IddCx slot pool
-        // 0x80070490. Active falls through to the JOIN path below (refcount++, no ADD).
+        // and wedges ADD at 0x80070490. Active falls through to the JOIN path below (refcount++, no ADD).
-        if matches!(*state, MgrState::Lingering { .. }) {
+        if matches!(*state, MgrState::Lingering { .. } | MgrState::Pinned { .. }) {
-            if let MgrState::Lingering { mon, .. } = std::mem::replace(&mut *state, MgrState::Idle)
+            let taken = match std::mem::replace(&mut *state, MgrState::Idle) {
-            {
+                MgrState::Lingering { mon, .. } | MgrState::Pinned { mon } => Some(mon),
+                other => {
+                    *state = other;
+                    None
+                }
+            };
+            if let Some(mon) = taken {
                 tracing::info!(
                     old_target = mon.target_id,
-                    "IDD-push reconnect — preempting the lingering monitor, recreating a fresh one"
+                    "IDD-push reconnect — preempting the kept (lingering/pinned) monitor, recreating a fresh one"
                 );
                 // SAFETY: `teardown` requires `dev` to be a valid control handle; `dev` is the value
                 // `ensure_device()` returned above (cached handles are never closed — a dead one is
@@ -458,12 +469,14 @@ impl VirtualDisplayManager {
             return Ok(self.output_for(mon));
         }
 
-        // Idle or Lingering: repurpose a lingering monitor / create a fresh one → Active{refs:1}.
+        // Idle or kept: repurpose a kept monitor / create a fresh one → Active{refs:1}. (In practice a
+        // kept Lingering/Pinned monitor was already preempted → Idle above; this arm is the defensive
+        // reuse path if a race left one here — it must stay exhaustive over `Pinned` regardless.)
         let mon = match std::mem::replace(&mut *state, MgrState::Idle) {
-            MgrState::Lingering { mut mon, .. } => {
+            MgrState::Lingering { mut mon, .. } | MgrState::Pinned { mut mon } => {
                 tracing::info!(
                     backend = self.driver.name(),
-                    "virtual monitor reused (reconnect within the linger window)"
+                    "virtual monitor reused (reconnect to a kept monitor)"
                 );
                 if mon.mode != mode {
                     // SAFETY: `reconfigure` needs an exclusive `&mut Monitor` and only touches the live
@@ -527,10 +540,14 @@ impl VirtualDisplayManager {
     ) -> Result<Monitor> {
         // Resolve the connecting client's STABLE per-client monitor id (so Windows reapplies its saved
         // per-monitor config — DPI scaling — on reconnect); `None`/anonymous → 0 = the driver
-        // auto-allocates the lowest-free id (the original slot-based behavior).
+        // auto-allocates the lowest-free id (the original slot-based behavior). The `identity` policy
-        let preferred_id = client_fp
+        // picks per-client vs per-client-mode; Windows defaults to PerClient (its historical behavior).
-            .map(|fp| self.identity_map.lock().unwrap().resolve(fp))
+        let preferred_id = super::identity::resolve_slot(
-            .unwrap_or(0);
+            client_fp,
+            (mode.width, mode.height),
+            crate::vdisplay::policy::Identity::PerClient,
+        )
+        .unwrap_or(0);
         // SAFETY: `create_monitor`'s own `# Safety` contract guarantees `dev` is the live control
         // handle; we forward it unchanged to `add_monitor`, whose precondition is exactly that.
         // `resolve_render_pin()` returns an `Option<LUID>` by value (plain `Copy`), so no borrowed
@@ -630,17 +647,36 @@ impl VirtualDisplayManager {
                 tracing::info!(backend = self.driver.name(), "target {} -> {n}", added.target_id);
                 // ADD only advertises the mode; force it active so DXGI captures the requested size.
                 set_active_mode(n, mode);
-                // Make the virtual display the SOLE active output (default): an EXTENDED (non-primary) IDD
+                // Apply the display-management topology (Stage 2). `Exclusive` (default) deactivates the
-                // isn't DWM-composited on this box → Desktop Duplication born-losts. Deactivating the other
+                // other display(s) so the IDD is the SOLE composited primary — an EXTENDED (non-primary)
-                // display(s) first via the atomic CCD path promotes the IDD to a composited primary with no
+                // IDD isn't DWM-composited on this box → Desktop Duplication born-losts. `Primary` keeps the
-                // MODE_CHANGE storm. Opt out with PUNKTFUNK_NO_ISOLATE=1.
+                // physical display(s) ACTIVE and makes the IDD primary (repositioned to origin). `Extend`
-                if std::env::var("PUNKTFUNK_NO_ISOLATE").is_err() {
+                // leaves it a plain extension. Both isolate + primary go through the atomic CCD path (no
-                    // SAFETY: `isolate_displays_ccd` is `unsafe` for its CCD topology FFI; it takes a
+                // MODE_CHANGE storm). Opt out (extend) with PUNKTFUNK_NO_ISOLATE=1 / the console policy.
-                    // `Copy` `u32` by value and returns an owned `SavedConfig` snapshot (no borrowed
+                use crate::vdisplay::policy::Topology;
-                    // memory crosses). It runs under the `state` lock, the sole mutator of the topology.
+                match topology_action() {
-                    ccd_saved = unsafe { isolate_displays_ccd(added.target_id) };
+                    // SAFETY (both arms): the CCD helper is `unsafe` for its topology FFI; it takes a
-                } else {
+                    // `Copy` `u32` by value and returns an owned `SavedConfig` (no borrowed memory crosses),
-                    tracing::info!("display isolation skipped (PUNKTFUNK_NO_ISOLATE) — IDD stays extended");
+                    // and runs under the `state` lock, the sole mutator of the topology.
+                    Topology::Exclusive => {
+                        ccd_saved = unsafe { isolate_displays_ccd(added.target_id) };
+                    }
+                    Topology::Primary => {
+                        // The IDD auto-activates as the SOLE display on a headless box, so the
+                        // physical (if present) is deactivated and QueryDisplayConfig sees only the
+                        // virtual. Force EXTEND first to (re)activate every CONNECTED display
+                        // alongside the virtual, THEN reposition to make the virtual primary — so the
+                        // physical stays active. (The bring-up above only force-EXTENDs when the
+                        // virtual FAILS to auto-resolve; here it resolved, so we do it explicitly.)
+                        unsafe { force_extend_topology() };
+                        thread::sleep(Duration::from_millis(300));
+                        ccd_saved = unsafe { set_virtual_primary_ccd(added.target_id) };
+                    }
+                    Topology::Extend | Topology::Auto => {
+                        tracing::info!(
+                            "display topology=extend — IDD stays extended (no isolate / no primary)"
+                        );
+                    }
                 }
                 thread::sleep(Duration::from_millis(1500)); // let the topology settle before capture opens
             }
@@ -725,7 +761,9 @@ impl VirtualDisplayManager {
     fn release(&self, gen: u64) {
         let mut state = self.state.lock().unwrap();
         let stale = match &*state {
-            MgrState::Active { mon, .. } | MgrState::Lingering { mon, .. } => mon.gen != gen,
+            MgrState::Active { mon, .. }
+            | MgrState::Lingering { mon, .. }
+            | MgrState::Pinned { mon } => mon.gen != gen,
             MgrState::Idle => true,
         };
         if stale {
@@ -736,6 +774,14 @@ impl VirtualDisplayManager {
                 mon,
                 refs: refs - 1,
             },
+            // Last session left: keep the monitor forever (Pinned) under `keep_alive = forever`,
+            // else linger for the policy window before the timer tears it down.
+            MgrState::Active { mon, .. } if keep_alive_forever() => {
+                tracing::info!(
+                    "virtual-display: last session left — PINNED (keep_alive=forever); free via /display/release"
+                );
+                MgrState::Pinned { mon }
+            }
             MgrState::Active { mon, .. } => {
                 let ms = linger_ms();
                 tracing::info!(
@@ -890,10 +936,139 @@ fn resolve_render_pin() -> Option<LUID> {
     crate::win_adapter::resolve_render_adapter_luid()
 }
 
-/// Linger window before a session-less monitor is torn down (default 10 s; `PUNKTFUNK_MONITOR_LINGER_MS`).
+/// A read-only view of the managed monitor for the mgmt `/display/state` endpoint (Goal:
+/// display-management registry facade). Backend-neutral; the [`crate::vdisplay::registry`] facade
+/// maps it into the wire shape.
+pub(crate) struct ManagedInfo {
+    pub backend: &'static str,
+    pub mode: (u32, u32, u32),
+    /// `"active"` | `"lingering"` | `"pinned"`.
+    pub state: &'static str,
+    /// Milliseconds until a lingering monitor is torn down (`None` when active).
+    pub expires_in_ms: Option<u64>,
+    /// Live sessions holding the monitor.
+    pub sessions: u32,
+    /// The monitor's generation stamp — a stable-enough id for the `/display/release` slot arg.
+    pub gen: u64,
+}
+
+impl VirtualDisplayManager {
+    /// Snapshot the current monitor for the mgmt `/display/state` endpoint. `None` when Idle.
+    pub(crate) fn snapshot(&self) -> Option<ManagedInfo> {
+        let st = self.state.lock().unwrap();
+        let (mon, state, sessions, expires_in_ms) = match &*st {
+            MgrState::Idle => return None,
+            MgrState::Active { mon, refs } => (mon, "active", *refs, None),
+            MgrState::Lingering { mon, until } => {
+                let ms = until.saturating_duration_since(Instant::now()).as_millis() as u64;
+                (mon, "lingering", 0u32, Some(ms))
+            }
+            // Pinned (keep_alive=forever): kept indefinitely, no expiry — the console shows "Pinned".
+            MgrState::Pinned { mon } => (mon, "pinned", 0u32, None),
+        };
+        Some(ManagedInfo {
+            backend: self.driver.name(),
+            mode: (mon.mode.width, mon.mode.height, mon.mode.refresh_hz),
+            state,
+            expires_in_ms,
+            sessions,
+            gen: mon.gen,
+        })
+    }
+
+    /// Force-tear-down a kept (LINGERING **or** PINNED) monitor now (the `/display/release` endpoint) —
+    /// so a physical-screen user gets their screen back without waiting out the linger, and it is the §8
+    /// escape hatch that frees a `keep_alive=forever` (Pinned) monitor. An Active monitor is refused
+    /// (stopping a live session is session management, not display management). Returns `true` if a kept
+    /// monitor was released.
+    pub(crate) fn force_release(&self) -> bool {
+        let Some(dev) = self.device_handle() else {
+            return false;
+        };
+        let mut st = self.state.lock().unwrap();
+        if matches!(&*st, MgrState::Lingering { .. } | MgrState::Pinned { .. }) {
+            let mon = match std::mem::replace(&mut *st, MgrState::Idle) {
+                MgrState::Lingering { mon, .. } | MgrState::Pinned { mon } => Some(mon),
+                other => {
+                    *st = other;
+                    None
+                }
+            };
+            if let Some(mon) = mon {
+                // SAFETY: `teardown` needs a live control handle; `dev` is from `device_handle()`
+                // (cached handles are never closed — a dead one is retired, kept alive; see
+                // `DeviceSlot`). `mon` was moved out of the kept state under the `state` lock,
+                // so it is exclusively owned here — no aliasing.
+                unsafe { self.teardown(dev, mon) };
+                return true;
+            }
+        }
+        false
+    }
+}
+
+/// Snapshot the managed monitor, or `None` when no backend has initialised the manager yet (no
+/// session has ever run) or it is Idle. Safe to call per management request.
+pub(crate) fn snapshot() -> Option<ManagedInfo> {
+    VDM.get().and_then(VirtualDisplayManager::snapshot)
+}
+
+/// Force-release a lingering monitor now; `false` if nothing was lingering (or the manager is
+/// uninitialised).
+pub(crate) fn force_release() -> bool {
+    VDM.get()
+        .map(VirtualDisplayManager::force_release)
+        .unwrap_or(false)
+}
+
+/// Linger window before a session-less monitor is torn down. The console display-management policy
+/// wins when configured (`keep_alive`); otherwise the legacy `PUNKTFUNK_MONITOR_LINGER_MS` env knob,
+/// else the 10 s default.
 fn linger_ms() -> u64 {
+    use crate::vdisplay::policy::{prefs, Linger};
+    if let Some(eff) = prefs().configured_effective() {
+        return match eff.keep_alive.linger() {
+            Linger::Immediate => 0,
+            Linger::For(d) => d.as_millis() as u64,
+            // `forever` is handled BEFORE this by `keep_alive_forever()` in `release` (→ `Pinned`), so
+            // this arm is only reached defensively (e.g. a caller that resolves ms without the pin
+            // check) — fall back to the default rather than a huge linger.
+            Linger::Forever => 10_000,
+        };
+    }
     std::env::var("PUNKTFUNK_MONITOR_LINGER_MS")
         .ok()
         .and_then(|s| s.parse().ok())
         .unwrap_or(10_000)
 }
+
+/// Whether the configured console policy's `keep_alive` resolves to **forever** (`Pinned`) — the
+/// gaming-rig preset. `release` uses this to keep the last-released monitor indefinitely instead of
+/// lingering. Unconfigured hosts are never forever (default is a short linger).
+fn keep_alive_forever() -> bool {
+    use crate::vdisplay::policy::{prefs, Linger};
+    prefs()
+        .configured_effective()
+        .map(|eff| matches!(eff.keep_alive.linger(), Linger::Forever))
+        .unwrap_or(false)
+}
+
+/// The effective display topology for a freshly-created monitor (never `Auto`): the console policy's
+/// [`effective_topology`](crate::vdisplay::effective_topology) when configured, else the legacy
+/// `PUNKTFUNK_NO_ISOLATE` env knob (`Extend`) / `Exclusive` (today's default). `Extend` leaves the IDD
+/// extended; `Primary` makes it primary while keeping the physical(s) active; `Exclusive` disables the
+/// physical(s) so the IDD is the sole composited desktop.
+fn topology_action() -> crate::vdisplay::policy::Topology {
+    use crate::vdisplay::policy::Topology;
+    if crate::vdisplay::policy::prefs()
+        .configured_effective()
+        .is_some()
+    {
+        return crate::vdisplay::effective_topology();
+    }
+    if std::env::var("PUNKTFUNK_NO_ISOLATE").is_ok() {
+        Topology::Extend
+    } else {
+        Topology::Exclusive
+    }
+}

crates/punktfunk-host/src/windows/win_display.rs

@@ -18,11 +18,13 @@ use windows::Win32::Devices::Display::{
     DisplayConfigGetDeviceInfo, DisplayConfigSetDeviceInfo, GetDisplayConfigBufferSizes,
     QueryDisplayConfig, SetDisplayConfig, DISPLAYCONFIG_DEVICE_INFO_GET_ADVANCED_COLOR_INFO,
     DISPLAYCONFIG_DEVICE_INFO_GET_SOURCE_NAME, DISPLAYCONFIG_DEVICE_INFO_SET_ADVANCED_COLOR_STATE,
-    DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO, DISPLAYCONFIG_MODE_INFO, DISPLAYCONFIG_PATH_INFO,
+    DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO, DISPLAYCONFIG_MODE_INFO,
+    DISPLAYCONFIG_MODE_INFO_TYPE_SOURCE, DISPLAYCONFIG_PATH_INFO,
     DISPLAYCONFIG_SET_ADVANCED_COLOR_STATE, DISPLAYCONFIG_SOURCE_DEVICE_NAME,
     QDC_ONLY_ACTIVE_PATHS, SDC_ALLOW_CHANGES, SDC_APPLY, SDC_FORCE_MODE_ENUMERATION,
     SDC_SAVE_TO_DATABASE, SDC_TOPOLOGY_EXTEND, SDC_USE_SUPPLIED_DISPLAY_CONFIG,
 };
+use windows::Win32::Foundation::POINTL;
 use windows::Win32::Graphics::Gdi::{
     ChangeDisplaySettingsExW, EnumDisplaySettingsW, CDS_TEST, CDS_UPDATEREGISTRY, DEVMODEW,
     DISP_CHANGE_SUCCESSFUL, DM_BITSPERPEL, DM_DISPLAYFREQUENCY, DM_PELSHEIGHT, DM_PELSWIDTH,
@@ -353,6 +355,48 @@ pub(crate) type SavedConfig = (Vec<DISPLAYCONFIG_PATH_INFO>, Vec<DISPLAYCONFIG_M
 /// doesn't export it, so define it here.
 const DISPLAYCONFIG_PATH_ACTIVE: u32 = 0x0000_0001;
 
+/// Query the current ACTIVE display config (paths + modes), truncated to the real counts. `None` on
+/// API failure. Shared by [`isolate_displays_ccd`] (snapshot + per-attempt re-query) and
+/// [`count_other_active`].
+unsafe fn query_active_config() -> Option<SavedConfig> {
+    let mut np = 0u32;
+    let mut nm = 0u32;
+    if GetDisplayConfigBufferSizes(QDC_ONLY_ACTIVE_PATHS, &mut np, &mut nm).is_err() {
+        return None;
+    }
+    let mut paths = vec![DISPLAYCONFIG_PATH_INFO::default(); np as usize];
+    let mut modes = vec![DISPLAYCONFIG_MODE_INFO::default(); nm as usize];
+    if QueryDisplayConfig(
+        QDC_ONLY_ACTIVE_PATHS,
+        &mut np,
+        paths.as_mut_ptr(),
+        &mut nm,
+        modes.as_mut_ptr(),
+        None,
+    )
+    .is_err()
+    {
+        return None;
+    }
+    paths.truncate(np as usize);
+    modes.truncate(nm as usize);
+    Some((paths, modes))
+}
+
+/// Count currently-ACTIVE display paths whose target id != `keep_target_id` — i.e. displays that would
+/// still be lit besides the virtual one. `None` on query failure. Used to VERIFY isolation actually took.
+unsafe fn count_other_active(keep_target_id: u32) -> Option<u32> {
+    let (paths, _) = query_active_config()?;
+    Some(
+        paths
+            .iter()
+            .filter(|p| {
+                p.targetInfo.id != keep_target_id && p.flags & DISPLAYCONFIG_PATH_ACTIVE != 0
+            })
+            .count() as u32,
+    )
+}
+
 /// Robust display isolation via the CCD API. The naive GDI approach (EnumDisplayDevices +
 /// ChangeDisplaySettings) MISSES displays on a hybrid box — an iGPU-attached physical monitor isn't
 /// flagged `ATTACHED_TO_DESKTOP` in the GDI enum, so it's never detached and the secure desktop /
@@ -363,6 +407,61 @@ const DISPLAYCONFIG_PATH_ACTIVE: u32 = 0x0000_0001;
 // pub(crate) so vdisplay::pf_vdisplay can reuse this backend-neutral CCD isolation helper
 // (it operates on a real OS target id — a pf-vdisplay monitor's target_id qualifies).
 pub(crate) unsafe fn isolate_displays_ccd(keep_target_id: u32) -> Option<SavedConfig> {
+    // Snapshot the ORIGINAL active config ONCE for restore-on-teardown, before any changes.
+    let saved = query_active_config()?;
+
+    // Deactivate every non-keep display, then VERIFY and RETRY. A field-reported bug had a physical
+    // monitor STAY ACTIVE in exclusive mode, so we don't trust a single SetDisplayConfig: re-query the
+    // live topology each attempt and re-apply until ONLY the keep target is active. Secure-desktop
+    // correctness depends on this — the lock screen must not land on a stray panel while we stream.
+    for attempt in 1..=4u32 {
+        let (mut paths, modes) = query_active_config()?;
+        let mut others = 0u32;
+        for p in paths.iter_mut() {
+            if p.targetInfo.id == keep_target_id {
+                continue;
+            }
+            if p.flags & DISPLAYCONFIG_PATH_ACTIVE != 0 {
+                p.flags &= !DISPLAYCONFIG_PATH_ACTIVE; // mark this path inactive
+                others += 1;
+            }
+        }
+        // Commit the config. Even when nothing needed deactivating we re-commit: a legacy mode-set does
+        // NOT drive the IddCx adapter's EVT_IDD_CX_ADAPTER_COMMIT_MODES, and without COMMIT_MODES the OS
+        // never calls ASSIGN_SWAPCHAIN, so the driver receives no frames. SDC_FORCE_MODE_ENUMERATION
+        // forces the re-commit; SAVE_TO_DATABASE only in the sole-path case (matches prior behavior —
+        // don't permanently rewrite the user's multi-display layout; the teardown restore handles it).
+        let mut flags = SDC_APPLY
+            | SDC_USE_SUPPLIED_DISPLAY_CONFIG
+            | SDC_ALLOW_CHANGES
+            | SDC_FORCE_MODE_ENUMERATION;
+        if others == 0 {
+            flags |= SDC_SAVE_TO_DATABASE;
+        }
+        let rc = SetDisplayConfig(Some(paths.as_slice()), Some(modes.as_slice()), flags);
+
+        // VERIFY the OUTCOME (rc alone lies — a "successful" apply can leave a panel active): re-query
+        // and confirm no non-keep display survived. Only then is the virtual truly the sole desktop.
+        let survivors = count_other_active(keep_target_id).unwrap_or(0);
+        if survivors == 0 {
+            tracing::info!("display isolate (CCD): target {keep_target_id} is the SOLE active desktop (attempt {attempt}/4, deactivated {others}, rc={rc:#x})");
+            return Some(saved);
+        }
+        tracing::warn!("display isolate (CCD): {survivors} display(s) STILL active after attempt {attempt}/4 (deactivated {others}, rc={rc:#x}) — re-querying + retrying");
+        std::thread::sleep(std::time::Duration::from_millis(250));
+    }
+    tracing::error!("display isolate (CCD): FAILED to isolate target {keep_target_id} after 4 attempts — a non-virtual display stayed active (the field-reported exclusive-mode bug)");
+    Some(saved)
+}
+
+/// **Primary (topology=primary)** — make the virtual output the PRIMARY display while KEEPING every
+/// other display ACTIVE (unlike [`isolate_displays_ccd`], which deactivates them). Windows treats the
+/// display whose source sits at the desktop origin `(0,0)` as primary, so we move the virtual's source
+/// to `(0,0)` and shift every other active source to its right — all paths stay active. Done as ONE
+/// atomic CCD `SetDisplayConfig` (NOT GDI `CDS_SET_PRIMARY`, which storms
+/// `DXGI_ERROR_MODE_CHANGE_IN_PROGRESS` when another display is live — see [`set_active_mode`]).
+/// Returns the original config to restore on teardown.
+pub(crate) unsafe fn set_virtual_primary_ccd(keep_target_id: u32) -> Option<SavedConfig> {
     let mut np = 0u32;
     let mut nm = 0u32;
     if GetDisplayConfigBufferSizes(QDC_ONLY_ACTIVE_PATHS, &mut np, &mut nm).is_err() {
@@ -385,36 +484,45 @@ pub(crate) unsafe fn isolate_displays_ccd(keep_target_id: u32) -> Option<SavedCo
     paths.truncate(np as usize);
     modes.truncate(nm as usize);
     let saved = (paths.clone(), modes.clone());
-    let mut others = 0u32;
+
-    for p in paths.iter_mut() {
+    // The virtual output's source width, to lay the other displays out to its right.
-        if p.targetInfo.id == keep_target_id {
+    let virt_width = paths.iter().find_map(|p| {
+        if p.targetInfo.id != keep_target_id {
+            return None;
+        }
+        let idx = p.sourceInfo.Anonymous.modeInfoIdx as usize;
+        let m = modes.get(idx)?;
+        (m.infoType == DISPLAYCONFIG_MODE_INFO_TYPE_SOURCE)
+            .then(|| m.Anonymous.sourceMode.width as i32)
+    })?;
+    let others = paths.len().saturating_sub(1);
+
+    // Reposition each active path's SOURCE once: the virtual to (0,0) (= primary), the other
+    // displays PACKED left-to-right from the virtual's right edge — kept active, no overlap and no
+    // gap (vs. blindly shifting each by virt_width, which leaves a dead gap when EXTEND already
+    // placed them to the right). Dedup source-mode indices (a cloned group shares one).
+    let mut next_x = virt_width;
+    let mut done = std::collections::HashSet::new();
+    for p in paths.iter() {
+        let idx = p.sourceInfo.Anonymous.modeInfoIdx as usize;
+        if !done.insert(idx) {
             continue;
         }
-        if p.flags & DISPLAYCONFIG_PATH_ACTIVE != 0 {
+        let Some(m) = modes.get_mut(idx) else {
-            p.flags &= !DISPLAYCONFIG_PATH_ACTIVE; // mark this path inactive
+            continue;
-            others += 1;
+        };
+        if m.infoType != DISPLAYCONFIG_MODE_INFO_TYPE_SOURCE {
+            continue;
+        }
+        if p.targetInfo.id == keep_target_id {
+            m.Anonymous.sourceMode.position = POINTL { x: 0, y: 0 };
+        } else {
+            let w = m.Anonymous.sourceMode.width as i32;
+            m.Anonymous.sourceMode.position = POINTL { x: next_x, y: 0 };
+            next_x += w;
         }
     }
-    if others == 0 {
+
-        // The virtual path shows active in the CCD database (from set_active_mode's legacy
-        // ChangeDisplaySettingsExW), but a legacy mode-set does NOT drive the IddCx adapter's
-        // EVT_IDD_CX_ADAPTER_COMMIT_MODES — and without COMMIT_MODES the OS never calls
-        // ASSIGN_SWAPCHAIN, so the driver never receives composed frames. Force an explicit CCD
-        // SetDisplayConfig commit of the (sole) virtual path so the IddCx path actually activates.
-        // SDC_FORCE_MODE_ENUMERATION makes the OS re-enumerate + re-commit even though the CCD DB
-        // already lists the path active.
-        let rc = SetDisplayConfig(
-            Some(paths.as_slice()),
-            Some(modes.as_slice()),
-            SDC_APPLY
-                | SDC_USE_SUPPLIED_DISPLAY_CONFIG
-                | SDC_ALLOW_CHANGES
-                | SDC_SAVE_TO_DATABASE
-                | SDC_FORCE_MODE_ENUMERATION,
-        );
-        tracing::info!("display isolate (CCD): forced CCD re-commit of sole virtual path {keep_target_id} rc={rc:#x} (drives IddCx COMMIT_MODES → ASSIGN_SWAPCHAIN)");
-        return Some(saved);
-    }
     let rc = SetDisplayConfig(
         Some(paths.as_slice()),
         Some(modes.as_slice()),
@@ -424,9 +532,9 @@ pub(crate) unsafe fn isolate_displays_ccd(keep_target_id: u32) -> Option<SavedCo
             | SDC_FORCE_MODE_ENUMERATION,
     );
     if rc == 0 {
-        tracing::info!("display isolate (CCD): deactivated {others} other display(s) — SudoVDA target {keep_target_id} is now the sole desktop");
+        tracing::info!("display primary (CCD): virtual target {keep_target_id} set PRIMARY at (0,0); {others} other display(s) kept ACTIVE + packed to its right");
     } else {
-        tracing::warn!("display isolate (CCD): SetDisplayConfig failed rc={rc:#x} (tried to deactivate {others} path(s))");
+        tracing::warn!("display primary (CCD): SetDisplayConfig failed rc={rc:#x} (virtual {keep_target_id} primary, physicals kept)");
     }
     Some(saved)
 }

crates/punktfunk-tray/src/status.rs

@@ -33,6 +33,10 @@ pub struct Summary {
     pub native_paired_clients: u32,
     pub pin_pending: bool,
     pub pending_approvals: u32,
+    /// Virtual displays kept with no live session (lingering/pinned). `#[serde(default)]` so an older
+    /// host that doesn't send it deserializes as 0.
+    #[serde(default)]
+    pub kept_displays: u32,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, serde::Deserialize)]
@@ -71,6 +75,14 @@ impl TrayStatus {
                     s.version, sess.width, sess.height, sess.fps
                 ),
                 (_, true) => format!("punktfunk host {} — streaming", s.version),
+                // Idle, but surface a kept (lingering/pinned) display: it — and, under an exclusive
+                // topology, your physical monitors — is being held. Release it from the console.
+                _ if s.kept_displays > 0 => format!(
+                    "punktfunk host {} — idle · {} display{} kept",
+                    s.version,
+                    s.kept_displays,
+                    if s.kept_displays == 1 { "" } else { "s" }
+                ),
                 _ => format!("punktfunk host {} — idle", s.version),
             },
         }
@@ -432,6 +444,7 @@ mod tests {
             native_paired_clients: 2,
             pin_pending: false,
             pending_approvals: 0,
+            kept_displays: 0,
         }
     }
 

design/display-management.md

@@ -0,0 +1,905 @@
+# Virtual-display management & lifecycle policy — design
+
+> **Status (2026-07-05):** **Stages 0–5 (§6A) DONE + on-glass validated; keep-alive reconnect
+> hardened** (branch `display-mgmt-stage0`, not yet merged). Stage 5 §6A: display **groups**
+> (`registry::group_key` — one per desktop backend, each gamescope spawn its own), group-aware
+> `exclusive`/`primary` (KWin name-filter + first-slot-wins; Mutter `set_first_in_group`), **per-group
+> topology restore** (KWin restore floats through the group, runs on the last member's teardown), the
+> **layout engine** (`vdisplay/layout.rs`, auto-row + manual) + registry-driven `apply_position`, the
+> `PUT /display/layout` endpoint with group/position/index in `/display/state`, and the **web console
+> arrangement table** — **live-validated on KWin `.116` + Mutter `.21`** (group model, positions,
+> identity keying, group-aware exclusive/extend, 2 concurrent Mutter `RecordVirtual` monitors). The
+> Stage-3 **KDE scaling round-trip is now proven live** (set 150 %/125 % → disconnect → reconnect →
+> reapplied, seen in `kwinoutputconfig.json`). **Keep-alive reconnect hardening (`b53710d`, on-glass
+> validated with the probe):** a same-client reconnect **preempts its own zombie**
+> (`admission::preempt_same_identity` — fixes "reconnect within the idle-detection window lands on a
+> fresh SECOND display while the old one keeps streaming"), a **deliberate quit skips the linger**
+> (client closes with `QUIT_CLOSE_CODE` 0x51 → `registry::release(force_immediate)`; §5.1), and the QUIC
+> control-connection idle timeout (the disconnect-detection latency) is **host-tunable**
+> (`PUNKTFUNK_IDLE_TIMEOUT_MS` / `--idle-timeout-ms`, default 8 s). **Remaining Stage 5 = hardware-gated
+> residuals only**: the per-group physical-restore EFFECT (needs a monitor-attached Linux box — the
+> headless validation boxes report `also_disabled=[]`, so nothing is disabled to restore), wlroots
+> `exclusive` (needs a Sway box), Mutter `APPLY_TEMPORARY` disconnect-revert. See the **Status —
+> handoff** block under §11 for the per-stage state and key decisions (notably the Windows `reject`
+> default).
+> This doc designs a **policy layer on top of the
+> existing per-compositor `VirtualDisplay` backends** — user-configurable lifecycle (keep-alive
+> after disconnect), topology (primary / exclusive), conflict handling (what happens when a second
+> client wants a different mode), stable display identity (so desktop environments remember
+> per-client settings like scaling), and **multi-monitor** (several virtual displays forming one
+> desktop, fed by one client or by several). The `VirtualDisplay` trait and the per-backend
+> `create()` mechanics stay as they are; this layer decides *when* to create, *how many*, *how
+> long* to keep, *what else* to do to the topology, and *under which identity*.
+
+Companion docs: `design/implementation-plan.md` §6 (virtual displays), `design/vrr-plan.md`
+(pacing — out of scope here), `design/gamescope-multiuser.md` (per-session isolation — adjacent,
+not required).
+
+## 1. Goal
+
+Today the virtual-display behavior is hardcoded per platform and per backend:
+
+- A session's virtual output is created at connect and torn down (RAII) at session end — a
+  disconnect destroys the display, reshuffles the desktop, and (on gamescope bare-spawn) **kills
+  the running game**.
+- "Make the streamed output the sole desktop" is an env knob on Linux
+  (`PUNKTFUNK_KWIN_VIRTUAL_PRIMARY` / `PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY`, default-on for the
+  auto-detected desktop path) and default-on on Windows (`PUNKTFUNK_NO_ISOLATE` to opt out) —
+  and on Linux "primary" and "disable the other outputs" are conflated into one switch.
+- What happens when a second client connects is an emergent property of the platform: Linux
+  creates a second output (multi-view), Windows **reconfigures the shared monitor under the
+  live session** (join-path `reconfigure` in `vdisplay/windows/manager.rs::acquire`), GameStream
+  preempts.
+- Only Windows gives a client a stable monitor identity (`vdisplay/windows/identity.rs`), so only
+  Windows reapplies per-client display config (DPI scaling) across reconnects. On KDE every
+  session's output is `Virtual-punktfunk` at whatever mode — scaling has to be re-set per connect
+  and is shared across every client.
+- One session = exactly one display. A client with two physical monitors can only stream one;
+  a tablet can't join an existing streamed desktop *as a second monitor* on purpose (the Linux
+  multi-view behavior half-does it by accident, with no layout control).
+
+Goal: **one shared, documented configuration surface** — a small set of orthogonal options with
+safe defaults and selectable presets, stored host-side, editable from the web console, applied
+uniformly across the punktfunk/1 and GameStream paths and across all five backends (KWin,
+gamescope, Mutter, wlroots, Windows pf-vdisplay), each backend implementing what it can and
+**honestly declining** what it can't (the same honest-downgrade convention as 4:4:4/10-bit).
+
+## 2. What exists today (inventory)
+
+The asymmetry worth internalizing: **Windows already has most of the machinery; Linux has none.**
+
+| Mechanism | Windows (pf-vdisplay) | Linux (kwin/mutter/wlroots) | gamescope |
+|---|---|---|---|
+| Lifecycle owner | `VirtualDisplayManager` singleton — `Idle / Active{refs} / Lingering{until}` state machine, gen-stamped `MonitorLease` | none — session owns `VirtualOutput.keepalive`, capturer drop = teardown | managed path: debounced TV-session restore (`RESTORE_DEBOUNCE` 5 s) + warm-session reuse; spawn path: child dies with the session |
+| Keep-alive after disconnect | linger, default 10 s (`PUNKTFUNK_MONITOR_LINGER_MS`) | none | managed: 5 s debounce (hardcoded) |
+| Reuse on reconnect | join Active (refcount++) / adopt Lingering (with a dead-swapchain preempt for IDD) | none (always create fresh) | managed: reuses the warm session |
+| Primary / exclusive | `isolate_displays_ccd` (exclusive), default on, restore on teardown | `apply_virtual_primary` = primary **and** disable others, env-gated, restore on drop; Mutter `make_virtual_primary` = sole monitor (APPLY_TEMPORARY) | n/a (own nested session) |
+| Mode conflict | join-path silently reconfigures the shared monitor (last-wins) | each session gets its own output (multi-view) | managed: one session; spawn: one gamescope per client |
+| Stable identity | `identity.rs` — cert-fp → id 1..=15 (EDID serial + ConnectorIndex), LRU, persisted `pf-vdisplay-identity.json` | none — KWin output always named `punktfunk`, sway `HEADLESS-N`, Mutter auto-serial | n/a |
+| Multi-monitor | manager is single-monitor (driver supports 16 connectors) | N outputs happen to coexist (multi-view), no layout/group semantics | single-output nested session |
+
+Design consequence: the plan is **not** "build a manager" — it's (a) extract the state machine
+Windows already proved into a platform-neutral, unit-testable core, (b) give Linux the ownership
+split it's missing (manager owns the keepalive, session holds a lease), (c) put a typed policy
+in front of both, (d) extend identity to Linux where the compositor allows it, and (e) grow the
+slot model into display **groups** so multi-monitor is an arrangement of slots, not a new system.
+
+## 3. Architecture
+
+Three new pieces, layered strictly **above** the `VirtualDisplay` trait (no backend rewrite):
+
+```
+                       ┌────────────────────────────────────────────┐
+   mgmt API / console  │  DisplayPolicy  (vdisplay/policy.rs)       │  pure config: schema,
+   host.env compat ───▶│  presets · layout · validation · persist   │  presets, env-compat
+                       └───────────────┬────────────────────────────┘
+                                       │ read per acquire/release (live-reload)
+                       ┌───────────────▼────────────────────────────┐
+   punktfunk/1 session │  DisplayRegistry (vdisplay/registry.rs)    │  host-lifetime singleton:
+   GameStream session ─▶  acquire(identity, mode) → DisplayLease    │  owns ManagedDisplay slots
+   mgmt /display/state │  release(lease) · linger timer · groups    │  grouped per desktop,
+                       └───────┬────────────────────────┬───────────┘  drives the pure Lifecycle
+                               │ create()/drop keepalive │ reconfigure/topology/layout ops
+                  ┌────────────▼──────────┐   ┌──────────▼───────────────┐
+                  │ Linux backends        │   │ Windows                  │
+                  │ kwin · gamescope ·    │   │ VirtualDisplayManager    │
+                  │ mutter · wlroots      │   │ (existing; delegates its │
+                  │ (unchanged trait)     │   │ state decisions upward)  │
+                  └───────────────────────┘   └──────────────────────────┘
+```
+
+- **`vdisplay/policy.rs`** — the typed config (`DisplayPolicy`), preset expansion, JSON
+  persistence (`<config>/display-settings.json`, the `gpu-settings.json` pattern: sanitize on
+  load, atomic tmp+rename write), and the deprecated-env-knob mapping. 100 % pure and
+  unit-tested (the `pick_gamescope_mode` / `wiring_plan.rs` discipline).
+- **`vdisplay/lifecycle.rs`** — the pure state machine: per-slot
+  `Idle / Active{refs} / Lingering{until} / Pinned` plus the **admission decision function**
+  (given: policy, requesting identity, requested mode(s), current slots → `Create | Reuse |
+  Reconfigure | Join{at_mode} | Steal{victims} | Reject{reason}`). No I/O, no OS types — fully
+  proptest/unit-testable, shared verbatim by both platforms. `Pinned` is `Lingering` with no
+  deadline (keep-alive **forever**), releasable only via mgmt/teardown.
+- **`vdisplay/registry.rs`** — the host-lifetime singleton that owns `ManagedDisplay` slots
+  (the backend `VirtualOutput` **including its `keepalive`**, the identity slot, current mode,
+  group membership, topology-restore state) and executes the lifecycle decisions: calls
+  `VirtualDisplay::create`, holds keepalives past session end, runs the linger timer, applies
+  layout, exposes the mgmt snapshot. On Windows it wraps the existing `VirtualDisplayManager`
+  (which keeps its driver/CCD/preempt specifics — the IDD dead-swapchain preempt, the
+  WUDFHost-death preempt, `begin_idd_setup` — but reads its linger duration and join/steal
+  behavior from the policy instead of env/hardcode).
+
+### The ownership split (the one real refactor)
+
+Today `capture::capture_virtual_output(vout, …)` consumes the whole `VirtualOutput` — the
+capturer owns the keepalive, so capturer drop tears the display down. That coupling is exactly
+what makes keep-alive impossible on Linux. Split it:
+
+```rust
+pub struct DisplayLease { /* registry handle + gen stamp; Drop = release(refcount--) */ }
+pub struct CaptureSource {          // what capture actually needs — Copy-ish, no ownership
+    pub node_id: u32,
+    pub remote_fd: Option<OwnedFd>, // Mutter portal daemon (dup'd per capture attach)
+    pub preferred_mode: Option<(u32, u32, u32)>,
+    #[cfg(windows)] pub win_capture: Option<WinCaptureTarget>,
+}
+// registry.acquire(...) -> (DisplayLease, CaptureSource)
+```
+
+The `keepalive: Box<dyn Send>` moves into `ManagedDisplay` inside the registry. The session's
+pipeline holds the `DisplayLease` (mirrors the Windows `MonitorLease`, gen-stamped so a stale
+lease from a preempted display is a release-no-op — the proven pattern). `build_pipeline`'s
+`vd.create(mode)` call sites (`punktfunk1.rs`, `gamestream/stream.rs`, `spike.rs`) become
+`registry::acquire(...)`. Every failure/retry path keeps its shape — the retry-hold lease trick
+in `build_pipeline_with_retry` maps 1:1 onto a `DisplayLease`.
+
+**Re-capture on reuse** is per-backend (see §7): wlroots re-runs portal capture of the still-
+existing output; KWin/Mutter reconnect a PipeWire consumer to the kept node (validation item);
+gamescope re-discovers the nested compositor's node; Windows already re-targets. If re-capture
+of a kept display fails, the registry falls back to **teardown + fresh create** (bounded, inside
+the existing `build_pipeline_with_retry` budget) — keep-alive is an optimization, never a new
+failure mode.
+
+## 4. The configuration surface
+
+### 4.1 Schema (`<config>/display-settings.json`)
+
+```json5
+{
+  "version": 1,
+  // Convenience: a named preset. "custom" (or absent) = the explicit fields below rule.
+  // When a preset IS named, the fields below are ignored (the console writes one or the other).
+  "preset": "custom",
+
+  // How long a display (and, on gamescope, the nested session + game) survives after the last
+  // session detaches. "off" = teardown at session end. "forever" = until host stop / explicit
+  // release. Duration is seconds.
+  "keep_alive": { "mode": "duration", "seconds": 300 },   // "off" | {"duration", seconds} | "forever"
+
+  // What the host does to the box's display topology while virtual displays are up:
+  //   "extend"    – add the virtual display(s), touch nothing else
+  //   "primary"   – make the group's primary virtual display the OS primary; physical outputs
+  //                 stay enabled
+  //   "exclusive" – the managed virtual displays become the ONLY enabled outputs (physicals
+  //                 disabled, restored when the group's last display is torn down)
+  //   "auto"      – today's behavior: exclusive on the auto-detected desktop path & Windows,
+  //                 extend when the operator pinned a compositor/env said otherwise
+  "topology": "auto",
+
+  // Admission when a client connects while another client's display/session is live and the
+  // requested mode differs (same-client reconnect ALWAYS reuses/reconfigures its own display):
+  //   "separate" – give the new client its own virtual display ON THE SAME DESKTOP (bounded by
+  //                max_displays) — this is also the "many clients as monitors" mode, see §6A
+  //   "steal"    – stop the existing session(s), tear down / reconfigure, serve the new client
+  //   "join"     – admit the new client AT THE EXISTING MODE (Welcome/serverinfo reflect the
+  //                real mode — the honest-downgrade convention); never reconfigures under a
+  //                live session
+  //   "reject"   – refuse the new client with a clear handshake error
+  "mode_conflict": "separate",
+
+  // Stable display identity → desktop environments persist per-display config (KDE scaling):
+  //   "shared"          – one identity for everything (today's Linux behavior)
+  //   "per-client"      – one identity per paired client cert fingerprint (today's Windows);
+  //                       a multi-display client (§6B) gets one identity per (client, display #)
+  //   "per-client-mode" – one identity per (client, WxH) — distinct scaling per resolution,
+  //                       at the cost of identity slots (Windows has 15; LRU eviction)
+  "identity": "per-client",
+
+  // How the group's displays are arranged in the desktop coordinate space (§6.2):
+  //   "auto-row" – left-to-right in acquire order, top-aligned (deterministic default);
+  //                a §6B client's own monitor-arrangement hints override auto placement
+  //   "manual"   – per-identity-slot offsets below (console-arranged); wins over client hints
+  "layout": { "mode": "auto-row", "positions": { /* "<slot>": {"x": 0, "y": 0} */ } },
+
+  // Upper bound on simultaneously-live virtual displays (Active + Lingering + Pinned, across
+  // the whole group). Admission returns Reject/Steal (per mode_conflict) when full; a §6B
+  // AddDisplay beyond it is declined. Windows is additionally capped by the driver (see §7).
+  "max_displays": 4
+}
+```
+
+Deliberate non-options (rejected):
+
+- **Per-client policy overrides** — real, but v2. One host-global policy first; the schema keys
+  are chosen so a later `"clients": {"<fp>": {…}}` overlay is additive.
+- **Idle timeout for Pinned displays** ("forever but tear down after 24 h") — `keep_alive`
+  already expresses it as a long duration; don't add a second axis.
+- **Choosing the linger for capture-loss separately from clean disconnect** — the registry only
+  sees "last lease released"; the session layer already distinguishes and (see §5.1) an explicit
+  client **quit** bypasses keep-alive entirely.
+- **Per-display FEC/bitrate policy knobs** — bitrate stays session-negotiated per stream as
+  today; a multi-display session's per-display bitrates are the client's ask, not host policy.
+
+### 4.2 Precedence & live-reload
+
+`display-settings.json` (console-written) **>** deprecated env knobs **>** built-in defaults —
+the exact precedence convention the GPU preference set (`console preference >
+PUNKTFUNK_RENDER_ADAPTER > auto`). The policy is **read at each acquire/release**, not once at
+startup (it's file/registry state, not env — no `HostConfig` constraint), so a console change
+applies to the next connect/disconnect without a host restart, same contract as the GPU card
+("applies to the next session"). Env-knob compatibility mapping (all logged as deprecated when
+they take effect):
+
+| Legacy knob | Maps to |
+|---|---|
+| `PUNKTFUNK_MONITOR_LINGER_MS` | `keep_alive = duration(ms/1000)` (Windows) |
+| `PUNKTFUNK_NO_ISOLATE` | `topology = "extend"` (Windows) |
+| `PUNKTFUNK_KWIN_VIRTUAL_PRIMARY` / `PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY` | `topology = "exclusive"` when truthy, `"extend"` when explicitly `0` |
+
+The `apply_session_env` default-on write of `*_VIRTUAL_PRIMARY` for the auto-desktop path is
+**replaced** by `topology = "auto"` resolving to exclusive on that path — one fewer process-env
+mutation on the connect path (a small win for the env-race surface `ENV_LOCK` guards).
+
+### 4.3 Presets
+
+Presets are the documented, supported entry point; raw fields are the escape hatch. Expansion
+lives in `policy.rs` and is unit-tested so docs and code can't drift.
+
+| Preset | keep_alive | topology | mode_conflict | identity | layout | Story |
+|---|---|---|---|---|---|---|
+| `default` | 10 s | auto | separate | per-client | auto-row | Today's behavior, made explicit: short linger absorbs client hiccups/reconnects, streamed output is the sole desktop on the auto path, extra clients get their own view. |
+| `gaming-rig` | forever | exclusive | steal | per-client | auto-row | Dedicated headless/couch box: the game and its display survive disconnects indefinitely; whoever connects takes the box over ("the TV model"). |
+| `shared-desktop` | off | extend | separate | per-client | auto-row | Streaming a desktop someone may also use physically: never blank the real monitors, never keep ghost outputs, concurrent viewers each get a view. |
+| `hotdesk` | 5 min | exclusive | reject | per-client-mode | auto-row | One user at a time with fast reattach (roaming between own devices); a second user is told the box is busy; each device+resolution keeps its own scaling. |
+| `workstation` | 5 min | exclusive | separate | per-client | manual | The multi-monitor daily driver: your dual-monitor client gets both displays back exactly where you arranged them (§6B), or a tablet joins as a side monitor (§6A). |
+
+## 5. Option semantics in detail
+
+### 5.1 `keep_alive`
+
+**What survives.** The *display* (compositor output / IddCx monitor / spawned gamescope) and its
+topology state survive; the *session* (QUIC conn, capture stream, encoder, input devices, audio
+plumbing) does not. Concretely per backend, "the display survives" means:
+
+- **kwin / mutter / wlroots**: the output stays in the layout → windows don't reshuffle, a
+  running game keeps rendering at the client's mode, reconnect is fast (no create/negotiate).
+- **gamescope (bare spawn)**: the nested gamescope **and the game launched inside it keep
+  running** — this is the headline user value (Sunshine/Apollo-style detach/reattach) and the
+  reason `keep_alive` is worth building at all.
+- **gamescope (managed)**: the policy duration replaces the hardcoded 5 s
+  `RESTORE_DEBOUNCE` — the warm Steam session stays up for the window; `forever` means the TV
+  session is never auto-restored (release via console/tray).
+- **Windows**: the existing linger, plus `forever` = the `Pinned` state — **shipped** (`ccbd7e8`,
+  `MgrState::Pinned`; compile-verified on `.173`, on-glass Windows Pinned pending). Freed via
+  `POST /display/release` (`force_release` handles Pinned) — the §8 escape hatch. `gaming-rig` (the
+  `forever` preset) is no longer mgmt-rejected and is enabled in the console; **on-glass validated on
+  Linux** (`.116` KWin: normal disconnect → `pinned`, no expiry; Release frees it).
+
+**Rules.**
+- Input devices (uinput pads, libei/EIS contexts) stay session-scoped — a disconnect reads to
+  the game as "controller unplugged", which games handle. (Keeping pads alive for kept sessions
+  is a possible later refinement; do not build it now.)
+- The **launch command runs once per display creation, never per attach** — a reconnect to a
+  kept gamescope must not double-launch the game. Today launch already happens once per
+  `build_pipeline`-successful session; the invariant moves with the create into the registry.
+- An explicit client **quit** (a user "stop", not a network drop) bypasses keep-alive: tear down
+  now. **Implemented on punktfunk/1** (`b53710d`, on-glass validated): the client closes the QUIC
+  connection with `QUIT_CLOSE_CODE` (0x51, shared in `core::quic`); the host reads the
+  `ApplicationClosed` reason and does `registry::release(force_immediate)` → `Linger::Immediate` →
+  teardown, skipping the linger. `NativeClient::disconnect_quit()` + `punktfunk-probe --quit` drive
+  it; GameStream `cancel`/quit-app (`h_cancel`) + the five real clients sending the code are
+  follow-ups. A plain disconnect / connection loss honors the policy (lingers for reconnect).
+- A **same-client reconnect resumes** (never a fresh second display). A reconnect while the client's
+  own prior session is still `Active` — its QUIC idle timer hasn't fired, and detection lags a drop by
+  `max_idle_timeout` (default 8 s, host-tunable via `PUNKTFUNK_IDLE_TIMEOUT_MS` / `--idle-timeout-ms`)
+  — is recognised by `admission::preempt_same_identity` (same cert fingerprint): the host signals the
+  zombie's stop + waits the release grace, so it lingers and the reconnect **reuses** the kept display.
+  Without this, a reconnect inside the detection window landed on a fresh second display while the old
+  session kept streaming. **Implemented + on-glass validated** (`b53710d`); implements the "preempts
+  downstream" the admission layer already promised (§5.3).
+- Host shutdown tears everything down (RAII on exit, as today). A host crash leaves whatever
+  the OS reclaims — Wayland connections die with the process (compositor reclaims outputs),
+  spawned gamescopes die with the process group, the pf-vdisplay watchdog reaps monitors when
+  pings stop. No new orphan class.
+- `keep_alive` + `topology=exclusive` means **physical monitors stay dark after disconnect**
+  until linger expiry / release. This is intended (gaming-rig) but must be loud in the docs, and
+  the release-now escape hatch (§8) must exist in the same release that ships `forever`.
+
+### 5.2 `topology`
+
+Splits the currently-conflated "primary" knob into three honest levels, **group-aware** (§6.1):
+"exclusive" means *the managed virtual displays* are the only enabled outputs — never disable a
+sibling slot; restore fires when the group's last display drops. Per-backend mapping:
+
+| | extend | primary | exclusive |
+|---|---|---|---|
+| KWin | no-op | `kscreen-doctor output.X.primary` only | primary + disable non-managed others (today's `apply_virtual_primary` with a registry-driven filter, §6.1), restore-on-teardown |
+| Mutter | no-op | `ApplyMonitorsConfig` incl. physicals, virtual primary | today's sole-monitor config (`make_virtual_primary`) extended to include all group members |
+| wlroots | no-op | **unsupported** (no primary concept) → log + treat as extend | `swaymsg output <phys> disable` + re-enable on teardown (new, small) |
+| gamescope | n/a — the nested session *is* the whole world; all three resolve to no-op | | |
+| Windows | skip isolate (today's `PUNKTFUNK_NO_ISOLATE`) | CCD primary-only variant (new, small — `set_active_mode` already exists; primary without deactivation) | today's `isolate_displays_ccd`, extended to isolate to the SET of managed targets |
+
+Restore stays bound to **display teardown** (keepalive drop / `teardown()`), not session end —
+already true everywhere; keep-alive inherits it for free. The KWin restore-before-reclaim
+ordering (re-enable others *first* so KWin never sees zero enabled outputs) is preserved.
+
+`auto` resolves at acquire time: exclusive on Windows and on the Linux auto-detected-desktop
+path, extend under an explicit `PUNKTFUNK_COMPOSITOR` pin (the CI/test posture) — bit-for-bit
+today's defaults, so `default` preset = no behavior change.
+
+### 5.3 `mode_conflict`
+
+Enforced at **admission**, before the Welcome / RTSP launch, in the lifecycle decision function
+— so the client gets an honest answer, not a mid-build failure:
+
+- Applies only across **different clients** (identity ≠ identity). A same-client reconnect
+  always preempts its own zombie session / adopts its own kept display and reconfigures it to
+  the newly requested mode (today's behavior, now uniform on all platforms).
+- `separate` — allocate another slot in the desktop group (Linux multi-view today, upgraded
+  with layout — §6A; Windows: **requires the multi-monitor manager, §6.6** — until that stage
+  lands, `separate` on Windows resolves to `join` with a startup + docs warning rather than
+  silently doing something else).
+- `join` — the second client is admitted at the live display's mode. punktfunk/1: the Welcome's
+  `Config` carries the real mode (the client already renders what the Welcome says — the
+  4:4:4/10-bit honest-downgrade pattern). GameStream: serverinfo/RTSP negotiate the live mode.
+  **This replaces the Windows join-path's silent last-wins `reconfigure` under a live session**
+  — that current behavior becomes opt-in as `steal`.
+- `steal` — signal the victim sessions' stop flags (the machinery `begin_idd_setup` already
+  uses), wait the release grace, tear down or reconfigure, admit. Trust note: conflict policy
+  runs **after** the pairing gate, so on a default host only paired clients can steal; on an
+  `--open`/TOFU host any accepted client can — the docs call this out and recommend `reject`
+  for open hosts.
+- `reject` — punktfunk/1: a typed handshake refusal (extend the existing error path with a
+  `busy` reason string carrying the live mode + client label so the client UI can say "host is
+  streaming 2560×1440 to <name>"); GameStream: the 503/session-in-use answer Moonlight already
+  understands.
+
+Interaction with `--max-concurrent` (session bound) is unchanged and orthogonal: sessions and
+displays are different resources; `max_displays` bounds displays, the accept-loop permit bounds
+in-flight sessions. `join` deliberately lets N sessions share one display (that's today's
+Windows concurrency model).
+
+### 5.4 `identity` — stable displays, persistent scaling (the KDE ask)
+
+Two halves: an **identity map** (who gets which slot) and a **per-backend identity carrier**
+(how a slot becomes something the DE keys its config on).
+
+**Map** — generalize `vdisplay/windows/identity.rs` (it's already pure + unit-tested) into a
+platform-neutral `vdisplay/identity.rs`: key = client cert fp (plus display ordinal for a §6B
+multi-display client, plus WxH under `per-client-mode`), value = small stable slot id, LRU
+eviction at the platform cap, persisted `<config>/display-identity.json` (Windows migrates
+`pf-vdisplay-identity.json` on first load — read old path if new absent, write new).
+Anonymous/unpaired clients stay slot 0 = auto/shared. **GameStream clients get identities too**
+(improvement over today): the paired GameStream client cert fingerprint feeds the same map, so a
+Moonlight device also keeps its scaling — today `set_client_identity` is only wired on the
+punktfunk/1 path.
+
+**Carriers per backend:**
+
+- **Windows** — shipped: slot → EDID serial + IddCx ConnectorIndex; Windows keys
+  `PerMonitorSettings` (DPI scaling) on exactly that. Cap 15 (ConnectorIndex <
+  MaxMonitorsSupported=16). `per-client-mode` and per-display ordinals work unchanged but burn
+  slots faster — the LRU already handles pressure; document the trade-off.
+- **KWin** — the carrier is the **output name**: `stream_virtual_output(name, …)` becomes
+  `punktfunk-<slot>` → output `Virtual-punktfunk-<slot>`. KWin persists per-output config
+  (scale, transform, mode) in `kwinoutputconfig.json`, matching EDID-less outputs **by name** —
+  so a stable per-client name is precisely what makes KDE reapply that client's scaling.
+  Two validation items before relying on it (Stage 3 gate, §11):
+  1. confirm KWin ≥ 6.5.6 actually persists + reapplies scale for `Virtual-*` outputs;
+  2. confirm a *remembered mode* doesn't fight the freshly requested one (if KWin reapplies a
+     stale stored mode on output-added, our existing `set_custom_refresh`/mode apply must run
+     after and win — it already reads back the achieved mode, so a fight is at least visible).
+  Side effect worth having: distinct names also unclash concurrent sessions (today two
+  simultaneous KWin sessions both create `Virtual-punktfunk` and `set_custom_refresh` /
+  `other_enabled_outputs` match **by that shared name** — a latent multi-view bug this fixes).
+- **wlroots** — no rename and no settable description via IPC; headless outputs are
+  `HEADLESS-N` by creation order. Identity is therefore **not reliably carriable** → declared
+  unsupported (`shared` behavior regardless of setting; capability matrix + docs say so). The
+  single-session case is de-facto stable (`HEADLESS-1`), which users can pin in sway config —
+  document that recipe instead of pretending.
+- **Mutter** — `RecordVirtual` auto-generates the virtual monitor's serial; no public D-Bus
+  surface to control it → unsupported for now. Note for later: re-evaluate Mutter's
+  virtual-monitor D-Bus surface per GNOME release (tracked as an open item, not a promise).
+- **gamescope** — n/a: the client streams a whole nested session; scaling inside it is per-game.
+
+**Scale as a punktfunk-side option (small, high-value adjunct):** KWin's
+`stream_virtual_output` takes a `scale` argument we currently hardcode to `1.0`. Add an optional
+per-client `default_scale` (console-editable next to the device list) passed at create on KWin;
+on Windows scaling stays the OS's job (identity makes it persist). This gives HiDPI phones/
+tablets a correct-sized desktop on first connect, before any DE-side persistence exists. A
+client-requested scale hint in the Hello (trailing-byte back-compat, like the gamepad-pref byte)
+is future protocol growth — design it when a client actually wants to send it.
+
+## 6. Multi-monitor
+
+Two scenarios, deliberately separated because they differ ~10× in cost:
+
+- **§6A — many clients, one desktop ("second screen")**: each client device becomes one more
+  monitor of the same host desktop (tablet as a side monitor next to the laptop's stream).
+  Structurally this already half-exists on the Linux desktop compositors (`separate` gives
+  every client its own output on the shared desktop); what's missing is *intent*: layout
+  control, group-aware topology, and honest per-backend gating. **No protocol change** — it
+  ships on the registry work.
+- **§6B — one client, many displays**: a client with two physical monitors gets two virtual
+  displays, streamed as two video planes, presented one-per-monitor, arranged on the host to
+  mirror the client's physical arrangement. Needs protocol growth, N encoder pipelines, client
+  presenter work, and (on Windows) the multi-monitor manager. **punktfunk/1-native only** —
+  GameStream/Moonlight has no multi-display vocabulary and stays single-stream.
+
+### 6.1 Display groups (registry concept, serves both)
+
+`ManagedDisplay` slots gain a **group**: the set of displays sharing one desktop/session.
+
+- kwin / mutter / wlroots: one group per compositor session — every acquired slot joins it
+  (that *is* the shared desktop).
+- gamescope spawn: one group per spawned nested session. gamescope is single-output — a §6B
+  client asking N displays there resolves to 1, honestly (the extra `AddDisplay`s are declined).
+- Windows: one group (the desktop); slots = IddCx monitors (§6.6).
+
+Group-aware semantics — these fix latent issues even before multi-monitor ships:
+
+- **`exclusive` disables only non-managed (physical/bootstrap) outputs, never group members.**
+  Today's KWin `apply_virtual_primary` disables "everything not named `Virtual-punktfunk`" —
+  under Stage-3 per-slot names, a second session's exclusive would disable the *first* session's
+  live output. The filter must consult the registry (the set of managed output names), not one
+  hardcoded name. Same shape on Windows (`isolate_displays_ccd` isolates to the managed target
+  *set*) and Mutter (the sole-monitor config includes all group members).
+- **`primary` designates one group member** — for §6B the client marks which of its displays is
+  primary (its OS already knows); for §6A the first slot wins unless the console re-designates.
+- **Topology restore is per-group, not per-display** — the saved pre-stream config is restored
+  when the group's **last** member drops, never while siblings live. (Windows `SavedConfig` and
+  the KWin `restore` vec move from `Monitor`/`StopGuard` into the group record.)
+
+### 6.2 Layout
+
+The `layout` policy block (§4.1) controls where group members sit in the desktop space:
+
+- `auto-row` (default): left-to-right in acquire order, top-aligned — what compositors mostly
+  do anyway, made deterministic.
+- `manual`: per-identity-slot offsets, console-edited (an OS-settings-style drag mini-map is
+  the stretch UI; an x/y table ships first). Keyed by identity slot, so *client B's tablet
+  always reappears to the right of client A's monitor* — layout + identity compose.
+- A §6B client sends its real monitor arrangement as per-display position hints; they override
+  `auto-row` (mouse crossing between streamed monitors then matches the client's physical
+  layout) but lose to `manual` pins.
+
+Backend mapping — all existing tooling, no new protocols: KWin
+`kscreen-doctor output.X.position.x,y` (validate syntax the way `set_custom_refresh` did);
+wlroots `swaymsg output <n> position X Y`; Mutter logical-monitor positions in the same
+`ApplyMonitorsConfig` we already build; Windows CCD source origins in the same
+`SetDisplayConfig` path `isolate_displays_ccd` uses.
+
+**Host-side input routing.** §6A needs nothing (N clients inject into one desktop — already
+true today). §6B needs the injectors to map `(display, x, y)` → desktop coordinates using the
+group layout: per-backend work items — libei absolute positioning is per-region, the wlr
+virtual-pointer protocol binds to an output, Windows `SendInput` absolute is desktop-normalized
+(pure math off the group layout). Wire change in §6.3.
+
+Two realities to document, not engineer around: **cursor rendering is already correct** (every
+backend embeds the cursor per-output — KWin `POINTER_EMBEDDED`, the IDD's per-monitor
+composition — so it appears only on the stream it's on and "crosses" between monitors
+naturally), and **a §6A desktop has one cursor shared by all member clients** — exactly right
+for the one-user-two-devices case (touch the tablet, the cursor jumps there), chaotic for two
+people; genuinely independent users want gamescope multi-user
+(`design/gamescope-multiuser.md`), not groups.
+
+### 6.3 Protocol growth for §6B (punktfunk/1 only)
+
+Principle: **a display is one data-plane instance.** Don't touch the hardened core packet
+format — N displays = N × (encoder + send thread + core `Session` over its own UDP flow), one
+shared QUIC control connection, one set of session-scoped side planes (audio, mic, rumble,
+input). And **don't grow the Hello**: the handshake's back-compat idiom is single trailing
+bytes — a variable-length display list doesn't fit it, and it doesn't need to, because the
+control stream stays open after `Start` (Reconfigure/ClockProbe already ride it).
+
+- **Capability**: client advertises `VIDEO_CAP_MULTI_DISPLAY` (`video_caps` bit `0x10`); the
+  Welcome echoes the host's per-session display budget as one trailing byte (`max_displays`
+  remaining, `0`/absent = single-display host — old hosts are automatically honest).
+- **Negotiation**: the Hello/Welcome pair is untouched and establishes **display 0** exactly as
+  today (an old host serves a multi-monitor-capable client's primary display with zero special
+  cases). Extra displays negotiate post-`Start` on the control stream:
+  `AddDisplay { mode, position_hint, primary: bool } → DisplayAdded { index, config /* the same
+  honest per-display Config shape the Welcome carries: mode, bit depth, chroma, codec */ }` or
+  `DisplayDeclined { reason }`. `RemoveDisplay { index }` and a per-display `Reconfigure`
+  (index as a trailing byte on the existing message) complete the set — **client monitor
+  hotplug maps 1:1 onto Add/Remove mid-session.**
+- **Data plane**: `DisplayAdded` carries the flow binding (host UDP port / flow token) for that
+  display's own core `Session`. Per-flow crypto derives the AES-GCM nonce salts per
+  (direction, display index) — no salt reuse across flows; FEC domains are independent per flow
+  (loss on one display can't stall another) — this is why "one Session per display" beats
+  muxing display ids into the core packet format.
+- **Side planes**: pointer/touch events gain a display-index byte (same trailing-byte pattern
+  as the gamepad pref; absent = display 0); 0xCF host-timing and 0xCE HDR-metadata datagrams
+  gain the index the same way (a client mixing an HDR laptop panel + SDR external monitor gets
+  per-display grades). Audio/mic/rumble/gamepad stay session-scoped, untouched.
+- **Per-display honesty**: each display negotiates bit depth/chroma/codec independently through
+  the same resolve functions — a host that can afford HEVC Main10 on one head and only 4:2:0 on
+  the second says so in each `DisplayAdded.config`.
+- **Stats**: the stats-unification vocabulary (four measurement points, p50/p95 windows) gains
+  a display dimension — per-display series, HUD shows the focused display's equation
+  (`design/stats-unification.md` gets a §6B addendum; don't invent client-local stats).
+- **C ABI / connector**: `punktfunk_add_display` / per-display `next_au` routing (an index out
+  param on the existing call keeps the ABI additive), so PunktfunkKit/JNI stay on the shared
+  connector.
+
+### 6.4 Encoder & resource budget
+
+N displays = N encode pipelines. NVENC consumer session caps — and the existing auto 2-way
+**split-encode** above ~1 Gpix/s consuming *two* NVENC sessions for one stream — mean admission
+must budget: `DisplayAdded` is granted only if the encoder backend confirms capacity (extend the
+existing NVENC session accounting + the AMF/QSV probes with a `can_open_another()` check), and
+**split-encode is disabled for multi-display sessions** (displays win over split; a 5K@240
+single head is not the multi-monitor use case). `max_displays` bounds the group. Same idle-cost
+note as keep-alive: every added display composites + encodes at full rate. Bandwidth is
+per-display additive (two 4K heads ≈ 2× the bitrate): the per-host speed test's recommendation
+should be read **per session** and split across that session's displays — the client divides
+its ask, the host doesn't second-guess it (per-display bitrate is deliberately not host policy,
+§4.1).
+
+### 6.5 Client staging for §6B
+
+- **Linux GTK + Windows clients first** — natural multi-window presenters: one
+  window/fullscreen surface per display on the matching physical monitor, the existing capture
+  state machine extended to span them (pointer crossing between our fullscreen windows must not
+  release capture).
+- **macOS second** (multi-NSWindow across Screens; Spaces/fullscreen interplay is the risk).
+- **Android/iOS/tvOS: never advertise the capability** — single-display presenters. A phone or
+  tablet still participates in multi-monitor via §6A (it *is* a second monitor), which needs
+  nothing from those clients.
+
+### 6.6 Windows multi-monitor manager
+
+Previously an explicit non-goal; now a designed **final stage** — the single-monitor manager
+keeps working unchanged until it lands:
+
+- **Manager**: the singleton's `MgrState` becomes a map keyed by connector id; `lifecycle.rs`
+  is already written per-slot, so the Windows manager's delegation doesn't change shape. The
+  IDD reconnect preempts (dead-swapchain, WUDFHost-death) become per-slot.
+- **Driver**: pf-vdisplay already ADDs by connector id 1..=15 (the identity map's bound). The
+  sealed frame channel (`IOCTL_SET_FRAME_CHANNEL`) must become **per-monitor** — channel
+  messages carry the monitor id, reusing the multi-pad `pad_index` pattern (driver proto v3;
+  `design/idd-push-security.md` addendum: same unnamed-object + handle-dup broker per ring).
+  Driver work + CI + on-glass validation is exactly why this stage is last.
+- **Capture/encode**: one IDD-push capturer per monitor ring; budget per §6.4.
+- **CCD**: isolate/primary/layout already group-aware from §6.1/6.2.
+
+## 7. Per-backend capability matrix
+
+What each backend supports; unsupported cells resolve to the stated fallback and are surfaced in
+`GET /api/v1/display/state` per display (`"capabilities": [...]`) so the console can grey options
+out per-host instead of lying:
+
+| Capability | KWin | gamescope spawn | gamescope managed | gamescope attach | Mutter | wlroots | Windows |
+|---|---|---|---|---|---|---|---|
+| keep-alive (linger/forever) | ✅ hold the vout thread; re-attach PipeWire consumer to the kept node — **validate** | ✅ nested session + game survive; re-discover node | ✅ policy replaces the 5 s debounce | — (never owned it) | ✅ hold the D-Bus session; consumer re-attach — **validate** | ✅ output persists; fresh portal capture per attach (cleanest) | ✅ shipped incl. `Pinned` (forever) |
+| reconfigure kept display to a new mode | ✅ `set_custom_refresh` + kscreen mode | ✅ SIGKILL+respawn is the honest "reconfigure" (game restarts — docs say so) or decline → recreate | ✅ existing managed-mode set | — | ⚠ node is sized by negotiation; renegotiation unproven — fallback recreate | ✅ `output <n> mode --custom` | ✅ `reconfigure()` shipped |
+| topology: primary | ✅ | n/a | n/a | n/a | ✅ | ❌ → extend | ✅ (new, small) |
+| topology: exclusive | ✅ shipped (filter → group-aware) | n/a | n/a | n/a | ✅ shipped (→ group-aware) | ✅ (new, small) | ✅ shipped (→ group-aware) |
+| mode_conflict: separate / §6A group | ✅ multi-output | ✅ one gamescope per client (independent sessions, no shared desktop) | ❌ single session → steal/join/reject only | — | ✅ assumed — **validate ≥2 RecordVirtual monitors** | ✅ HEADLESS-N | ⏳ §6.6 (until then → join + warning) |
+| §6B multi-display for one client | ✅ N outputs + layout | ❌ single-output (extra displays declined) | ❌ | — | ⚠ gated on the ≥2-monitor validation | ✅ | ⏳ §6.6 |
+| layout (position control) | ✅ kscreen position | n/a | n/a | n/a | ✅ ApplyMonitorsConfig | ✅ `output position` | ✅ CCD origins |
+| stable identity | ✅ output name per slot | n/a | n/a | n/a | ❌ (API gives no serial control) | ❌ (no name control) | ✅ shipped |
+
+The **attach** gamescope sub-mode never owns the display (it mirrors a foreign gamescope) — the
+registry records it as an unmanaged pass-through slot: no keep-alive, no topology, no identity,
+conflict = join-only. That's just codifying reality.
+
+## 8. Management API, web console, tray
+
+Endpoints (bearer-only, like `/gpus`; documented in `mgmt.rs`'s OpenAPI → regenerate
+`api/openapi.json`):
+
+- `GET /api/v1/display/settings` → `{ settings, preset_expansions, capabilities }` — the stored
+  policy plus what this host's live backend can actually do (so the console renders accurate
+  controls).
+- `PUT /api/v1/display/settings` — validate (unknown fields rejected, ranges clamped like the
+  GPU PUT), persist atomically, log. Applies from the next acquire/release.
+- `GET /api/v1/display/state` → live slots:
+  ```json
+  { "displays": [ { "slot": 3, "backend": "kwin", "output": "Virtual-punktfunk-3",
+      "mode": "2560x1440@120", "state": "lingering", "expires_in_s": 240,
+      "client": "a1b2c3…(label)", "display_index": 0, "sessions": 0,
+      "group": 1, "position": {"x": 0, "y": 0}, "topology": "exclusive" } ] }
+  ```
+- `POST /api/v1/display/release` `{ "slot": 3 }` or `{}` (all) — immediately tear down
+  Lingering/Pinned displays. **Refuses Active** (stopping a live session is session management,
+  not display management — don't blur it).
+- `PUT /api/v1/display/layout` `{ "positions": { "<slot>": {"x":…, "y":…} } }` — the manual
+  arrangement (applies live to affected groups; persisted into the policy's layout block).
+
+Web console (Host page, next to the GPU card): a **Virtual displays** card — preset selector
+(radio + one-line story each, `custom` unlocking the advanced fields), the live display list from
+`/state` with per-row "Release" buttons and a linger countdown, the arrangement editor (x/y
+table first, drag mini-map stretch), capability-aware disabled states. The loopback
+`local/summary` gains a `displays_live` count (counts only — the established no-secrets rule) so
+the **tray** tooltip can show "1 display kept alive" and offer a release-all action through the
+same elevation path as start/stop (Windows) / `systemctl --user` (Linux) — tray work is a
+stretch stage, not core.
+
+## 9. Enforcement points (exact code paths)
+
+1. **punktfunk/1 handshake** (`punktfunk1.rs`, where the Hello is resolved into the Welcome):
+   call `registry::admit(identity, requested_mode)` → on `Reject` answer the typed refusal; on
+   `Join` the Welcome's `Config` carries the live mode; on `Steal` signal victims + wait release
+   (bounded) before proceeding. This runs **before** `SessionContext` is built.
+2. **`virtual_stream` / `build_pipeline`** (`punktfunk1.rs:3511`, `build_pipeline_with_retry`):
+   `vd.create(mode)` → `registry::acquire(...) -> (DisplayLease, CaptureSource)`; the retry-hold
+   lease keeps its exact semantics. The mid-stream **Reconfigure**, **session-switch**, and
+   **capture-loss rebuild** paths re-acquire through the registry so a compositor switch
+   correctly releases the old backend's slot and the new mode updates the slot's record.
+3. **Control stream, post-Start** (§6B): `AddDisplay`/`RemoveDisplay` handlers spawn/stop a
+   per-display pipeline (its own `registry::acquire`, encoder, send thread, UDP flow) inside the
+   same `SessionContext` lifetime; `--max-concurrent` counts sessions, not displays.
+4. **GameStream** (`gamestream/stream.rs::open_gs_virtual_source`): same acquire; identity from
+   the paired client cert fp (new); quit-app → `release(quit=true)` which bypasses keep-alive.
+5. **Session end**: capturer drop (releases the PipeWire consumer / ring) then `DisplayLease`
+   drop → lifecycle decides Linger/Pinned/teardown. On Linux the keepalive no longer rides the
+   capturer (§3 ownership split).
+6. **`serve` startup/shutdown**: registry constructed once (like `start_restore_worker`), all
+   slots torn down on graceful exit.
+
+## 10. Documentation plan
+
+A dedicated docs-site page **`docs-site/content/docs/virtual-displays.md`** (+ `meta.json`
+entry), cross-linked from `configuration.md`, `host-cli.md`, `steamos-host.md`, and
+`troubleshooting.md`. Structure — written for the operator, presets first:
+
+1. **What punktfunk does with displays** — 5 lines: per-client-sized virtual output, created on
+   connect, what "keep alive"/"exclusive" mean physically.
+2. **Pick a preset** — the §4.3 table verbatim, each with a one-paragraph story and the JSON it
+   expands to ("copy this into display-settings.json, or click it in the console").
+3. **Options reference** — one subsection per option: values, default, per-backend support
+   badge row, and a concrete example scenario each ("You stream from your phone at 1080p and
+   your TV at 4K120: with `identity: per-client` KDE remembers 150 % scaling for the phone and
+   100 % for the TV").
+4. **Multi-monitor** — the two scenarios in user language: *"use your tablet as a second
+   monitor"* (§6A: connect a second device, arrange it in the console) and *"stream your
+   dual-monitor setup"* (§6B: which clients support it, what the host does with the layout),
+   plus the support matrix and the GameStream single-stream note.
+5. **Persistent scaling (KDE/Windows)** — the user-visible recipe: connect once, set scaling in
+   System Settings / Windows Settings while streaming, done — punktfunk's stable identity makes
+   the DE reapply it. Honest support table (KWin ✅ / Windows ✅ / GNOME ❌ why / Sway recipe).
+6. **Troubleshooting** — "my physical monitors stayed off" → release button/endpoint + the
+   keep_alive×exclusive explanation; "second client gets the wrong resolution" → `join`
+   semantics; "game restarted on reconnect" → gamescope reconfigure caveat; "second display
+   declined" → encoder budget (§6.4); KWin/gamescope version floors.
+7. **Legacy env knobs** — the §4.2 mapping table, marked deprecated.
+
+Also update: `README.md` status row, `CLAUDE.md` (status + invariant below), `host.env.example`
+(point at the JSON/console, list deprecated knobs), and the OpenAPI snapshot.
+
+**New design invariant for CLAUDE.md** (once shipped): *Display lifecycle is owned by the
+registry, policy-driven; sessions hold leases, never the keepalive. New backends implement
+`VirtualDisplay` + declare capabilities; they never grow their own lifecycle/env knobs. A
+display is one data-plane instance — multi-display never muxes into the core packet format.*
+
+## 11. Staged implementation
+
+Each stage lands green (`cargo test/clippy/fmt`, OpenAPI drift check) and is independently
+shippable; on-glass validation notes inline. **Heads-up for this box:** the dev VM currently has
+no GPU passthrough (RTX 5070 Ti detached at the Proxmox level, 2026-07-01) — KWin-path live
+validation needs the GPU back or one of the LAN hosts.
+
+### Status — 2026-07-05 handoff
+
+Branch **`display-mgmt-stage0`** (NOT merged; merge when the whole feature is polished/complete).
+On-glass validation boxes: **`.173`** (Windows, pf-vdisplay + a physical monitor), **`.21`** (CachyOS
+GNOME/Mutter, RTX 5070 Ti), **`.116`** (Bazzite KDE/KWin, AMD — build via a `fedora:43` distrobox;
+`.48` Fedora KDE is DOWN). Every commit is `cargo test/clippy/fmt`-green.
+
+- **Stages 0–4: DONE + on-glass validated.** 0 (policy surface + `/display/settings` + console card),
+  1 (pure `lifecycle.rs` + `registry.rs` Linux keep-alive pool + ownership split via `DisplayLease` +
+  `/display/state`/`/display/release`), 2 (topology decoupling — distinct `extend`/`primary`/`exclusive`
+  via `effective_topology()`), 3 (platform-neutral `identity.rs` map + `per-client-mode` + KWin per-slot
+  output naming → **KWin persists per-output scale by name**, proven via `kwinoutputconfig.json` on `.116`),
+  4 (mode-conflict admission — `vdisplay/admission.rs`, loopback-validated for all four policies).
+- **Stage 5 (§6A): DONE + on-glass validated (KWin `.116` + Mutter `.21`).** All §6A group semantics
+  landed + unit-tested, then live-validated (group model, positions, identity keying, group-aware
+  exclusive/extend, 2 concurrent Mutter `RecordVirtual` monitors; the dev VM itself is GPU-less):
+  **display groups** (`registry::group_key` — one
+  per desktop backend, each gamescope spawn its own group), **group-aware exclusive/primary** (KWin
+  `MANAGED_PREFIX` + first-slot-wins; Mutter `set_first_in_group` → a non-first session extends rather than
+  re-clobbering), **per-group topology restore** (KWin hands its restore to the registry via
+  `take_topology_restore`; `Entry::topology_restore` + `hand_off_restore` float it to a surviving sibling
+  and run it only when the group empties, before the last output drops — all 3 teardown paths), the pure
+  **layout engine** (`vdisplay/layout.rs::arrange`, auto-row + manual) + **registry-driven `apply_position`**
+  (`position_for_new` over the whole group; skips the origin so the single-display path is unchanged), the
+  `PUT /api/v1/display/layout` endpoint (`EffectivePolicy::with_manual_layout`), and `/display/state` now
+  carrying `group`/`display_index`/`position`/`identity_slot`/`topology`. The registry keys the arrangement
+  on per-client identity via `VirtualDisplay::last_identity_slot` (KWin). The **web arrangement table**
+  (`DisplayCard.tsx` `DisplayArrangement`, en+de) is also done, moved to its own **Virtual displays** nav
+  section with a full one-click-preset config surface. **Remaining = hardware-gated residuals only:** the
+  per-group physical-restore EFFECT (needs a monitor-attached box — the headless boxes report
+  `also_disabled=[]`), wlroots `exclusive` (needs a Sway box), Mutter `APPLY_TEMPORARY` disconnect-revert —
+  see the Stage 5 entry below. Plus the **keep-alive reconnect hardening** (`b53710d`, on-glass validated):
+  same-client zombie preempt + deliberate-quit skip-linger + tunable idle timeout (§5.1) — what made
+  "reconnect resumes" actually hold under a fast reconnect.
+
+**Decisions / deltas from this plan as written — read before continuing:**
+- **Windows admission default is `reject`, NOT `join`** (supersedes the Stage-4 line below). Two
+  concurrent Windows sessions both drive one pf-vdisplay monitor's **single-capturer** IDD-push channel
+  (newest-delivery-wins) → the 2nd freezes + can WEDGE the 1st (observed live: it wedged `.173`, needed a
+  reboot — surfaced as Moonlight "no video"). True multi-session Windows capture is §6.6/Stage 7. So on
+  Windows `separate` (incl. the unconfigured default) resolves to `reject` — a 2nd client gets a clean
+  503, the live session is protected; `join`/`steal` are explicit opt-ins. Centralised in
+  `admission::effective_conflict()`, shared by the native handshake + GameStream `h_launch`.
+- **Reject IS typed:** punktfunk/1 closes the QUIC connection with app code `0x42` + the reason
+  `"host busy: streaming WxH@Hz to <client>"`, which the client reads from `ApplicationClosed`.
+- **Stage 5's group-aware exclusive fixes a bug Stage 3 introduced:** per-slot names meant a 2nd
+  `exclusive` session's disable-filter would black out the 1st session's `Virtual-punktfunk-<id>` output.
+  Fixed on KWin by recognising the whole managed group via the shared `Virtual-punktfunk` prefix.
+- **GameStream 503** is implemented (owner-fp on `LaunchSession`, `gamestream_admission()` unit-tested,
+  shares `effective_conflict()`) but NOT Moonlight-validated (can't drive `/launch` autonomously).
+
+**Validated since (2026-07-05):** the KWin **set-scaling ROUND-TRIP** — a client set 150 % then 125 %
+in the streamed KDE session, disconnected, reconnected, and the scale was reapplied to the freshly
+re-created `Virtual-punktfunk-<id>` (proven in `kwinoutputconfig.json`); this closes the Stage-3 gate.
+Also the §6A group model + group-aware exclusive/extend + 2 concurrent Mutter `RecordVirtual` monitors,
+and the keep-alive reconnect hardening.
+
+**Still deferred (need a display-attached box / a specific compositor / a real client):** the `primary`
+physical-keep EFFECT on Linux + a Windows primary-only CCD variant; **wlroots `exclusive`**; GameStream
+503 on-glass; and the **per-group physical-restore EFFECT** — a monitor-attached box is required to see
+`exclusive` disable a physical output and the group restore re-enable it only after the last member drops
+(the headless boxes report `also_disabled=[]`, so the group semantics are proven but the physical
+toggle isn't).
+
+- **Stage 0 — policy + plumbing-lite. [DONE ✓]** `policy.rs` (schema/presets/persist/env-compat, fully
+  unit-tested), mgmt GET/PUT `/display/settings`, console card (settings only), docs page
+  skeleton with the presets/options tables. Behavior deltas limited to what existing knobs can
+  express: Windows linger reads the policy; Linux topology auto/extend/exclusive routes through
+  the existing primary code. *No lifecycle change yet — zero-risk adoption of the surface.*
+- **Stage 1 — lifecycle core + Linux keep-alive. [DONE ✓]** `lifecycle.rs` pure machine
+  (+proptests: no lost teardowns, no double-frees across arbitrary acquire/release/expiry
+  interleavings), `registry.rs`, the ownership split (`DisplayLease`/`CaptureSource` — the one
+  cross-cutting refactor, touches `capture_virtual_output` signatures on both OSes), keep-alive
+  live for **wlroots** and **gamescope-spawn** (the two backends where reuse is structurally
+  trivial), `/display/state` + `/display/release`, console live-list. Windows manager delegates
+  linger/pinned decisions to `lifecycle.rs` (its driver specifics untouched).
+  *Validate:* sway on this box (headless), gamescope spawn: connect → disconnect → verify
+  vkcube/game still runs → reconnect → same session, no relaunch.
+- **Stage 2 — topology decoupling. [DONE ✓]** Kept-node PipeWire re-attach on
+  KWin and Mutter (each behind its validation; fallback recreate), `primary` (without disable)
+  on KWin/Mutter/Windows, `exclusive` on wlroots, restore paths regression-tested.
+  *Validate:* headless KDE session (the `run-headless-kde.sh` rig), GNOME box .248.
+- **Stage 3 — identity. [DONE ✓]** Platform-neutral identity map + migration, per-slot KWin output
+  naming (+ the concurrent-session name-clash fix riding along), GameStream identity wiring,
+  optional `per-client-mode` keying, per-client `default_scale` on KWin.
+  *Validated on KDE (`.116`, 2026-07-05):* a client set 150 % then 125 % in the streamed session,
+  disconnected, reconnected (keep-alive off → full teardown+recreate), and the scale was reapplied to
+  the fresh `Virtual-punktfunk-<id>` — confirmed in `kwinoutputconfig.json` (`scale=1.25` persisted by
+  connector name). This is the round-trip the persist mechanism was designed for. *(client-B-unaffected
+  under two concurrent sessions is folded into the Stage-5 two-session case.)*
+- **Stage 4 — mode-conflict admission. [DONE ✓]** Decision function (`vdisplay/admission.rs`,
+  `decide`/`admit`/`effective_conflict`) wired into the punktfunk/1 handshake + GameStream `h_launch`,
+  the typed punktfunk/1 `busy` refusal (QUIC close `0x42` + reason), GameStream 503 path, `steal`
+  victim signaling reusing the stop-flag plumbing. **The Windows default is `reject`, NOT the
+  `join`/silent-reconfigure originally planned** — see the handoff Decisions above (single-capturer
+  IDD-push). Loopback-validated (all four policies) + `.173` reject-default validated; GameStream 503
+  unit-tested, Moonlight-pending.
+- **Stage 5 — §6A multi-client monitors. [DONE ✓ — on-glass validated (KWin `.116` + Mutter `.21`); hardware-gated residuals deferred]** Display
+  groups, group-aware exclusive/primary/restore (incl. the name-filter fix), layout auto-row + manual,
+  `/display/layout`, console arrangement table. Cheap: rides Stages 1–3 infrastructure, no protocol change.
+  **Done:**
+  - KWin group-aware `exclusive` (the name-filter fix — recognise the managed group by the
+    `Virtual-punktfunk` prefix instead of one hardcoded name) + first-slot-wins for the group primary,
+    unit-tested.
+  - **Layout engine** (`vdisplay/layout.rs::arrange`): pure auto-row (left-to-right in acquire order,
+    top-aligned) + manual (per-identity-slot offsets, auto-row fallback for unpinned members),
+    unit-tested. `manual_position` helper for a single backend-local apply.
+  - **Registry group model** (Linux): group = backend (one desktop per compositor session); the
+    `/display/state` snapshot groups entries, orders by acquire (gen), and computes each member's
+    `position` via the engine. `DisplayInfo` now carries `group` / `display_index` / `position` /
+    `identity_slot` / `topology`. The backend reports its resolved slot via the new
+    `VirtualDisplay::last_identity_slot` (KWin only), so the arrangement + state key on per-client identity.
+  - **`PUT /api/v1/display/layout`**: persists the console's manual arrangement (positions keyed by
+    identity slot) via the pure `EffectivePolicy::with_manual_layout` transform (locks the current
+    effective behavior into explicit `Custom` fields + sets a manual layout — arranging is orthogonal to
+    the other axes). OpenAPI regenerated.
+  - **Registry-driven position apply** (`VirtualDisplay::apply_position(x, y)`, default no-op; KWin
+    implements it via `kscreen-doctor output.<n>.position.<x>,<y>`): the registry owns the group, so
+    right after `create` it computes the new display's position over the whole group via the pure
+    `position_for_new` (existing same-backend members in acquire order + the new one appended last →
+    `layout::arrange` → the new member's placement) and calls `apply_position`. This makes **both**
+    auto-row (deterministic left-to-right, not just the compositor's default) **and** manual placement
+    go through one seam. Guarded: the registry skips the desktop origin `(0, 0)`, so a single-display /
+    first-of-group session (and every non-KWin backend, which no-ops `apply_position`) issues no
+    positioning at all — the historical single-display path is byte-for-byte unchanged. `position_for_new`
+    is unit-tested. *On-glass-validation-pending (kscreen positioning of a live virtual output).*
+  - **Per-group topology restore** (design §6.1 — restore the physical only when the group's LAST member
+    drops): the KWin `exclusive` restore no longer rides the per-session `StopGuard` (which would re-enable
+    the physical the moment the FIRST of several exclusive sessions dropped, under a live sibling). KWin
+    now hands the restore to the registry as a closure (`take_topology_restore`); the registry keeps it in
+    the display **group** (`Entry::topology_restore`) and, on teardown, **floats** it to a surviving
+    same-group sibling (`hand_off_restore`) or, when the group empties, runs it — outside the lock, BEFORE
+    the last output's keepalive drops, so the compositor never sees zero outputs. All three teardown paths
+    (lease drop / linger expiry / mgmt release) honor it. The single-display path is byte-for-byte
+    unchanged (one member → run on its teardown). `hand_off_restore` is unit-tested (float / run-on-last /
+    non-carrier-first / never-cross-backend). *Residual concurrent-connect race + two-session on-glass
+    validation pending.*
+  - **Mutter group-aware** (`set_first_in_group`): the registry tells each backend whether it is the
+    FIRST display of its group; a non-first Mutter session **extends** into the already-exclusive desktop
+    instead of re-applying a sole-monitor `ApplyMonitorsConfig` that would disable the first session's
+    virtual. (Simpler than the originally-planned "include all group virtuals," which Mutter can't do —
+    its connectors are un-nameable — and achieves the same connect-time outcome.) Single-session unchanged
+    (`first == true`). *Residual: Mutter `APPLY_TEMPORARY` reverts the topology when the FIRST session
+    leaves under a live sibling (§7) — a full fix needs a group-owned `DisplayConfig` connection; deferred.
+    Concurrent-Mutter on-glass validation pending (even ≥2 `RecordVirtual` monitors is unproven).*
+  - **gamescope groups** (design §6.1): a gamescope **spawn** is an independent nested session per client
+    (no shared desktop), so `registry::group_key` makes each gamescope display its OWN group — never
+    auto-rowed against, topology-grouped with, or restore-grouped with another gamescope. Unit-tested.
+    (§6B single-output "decline extras" is Stage 6.)
+  - **Console arrangement table (web)** [DONE ✓]: a `DisplayArrangement` x/y editor in the `Virtual
+    displays` card (`web/src/sections/Host/DisplayCard.tsx`) — for a ≥2-display group it renders an x/y
+    table over the live displays that carry an identity slot, seeded from `/display/state`, and Save
+    writes `PUT /display/layout` (switches the host to a manual layout, applied next connect). en+de
+    i18n; the stale `display_pending_note` copy refreshed. tsc + vite build green. (Drag mini-map is a
+    later stretch.)
+  **Remaining Stage 5 — hardware-gated residuals only (no more host/web build work):**
+  - **On-glass validation — mostly DONE (2026-07-05, KWin `.116` + Mutter `.21`):** the group model,
+    per-member positions, identity keying, group-aware `exclusive`/`extend` coexistence (a 2nd session
+    does NOT clobber the 1st's output), and **2 concurrent Mutter `RecordVirtual` monitors** are all
+    confirmed live; the keep-alive reconnect path (reuse, quit-skip-linger, tunable idle) was validated
+    deterministically with the probe. **STILL PENDING: the per-group physical-restore EFFECT** — both
+    boxes are headless so `also_disabled=[]` (nothing to disable → nothing to restore); seeing
+    `exclusive` black out a real monitor and the group restore re-enable it only after the LAST member
+    drops needs a **monitor-attached Linux box**. The group-restore LOGIC (`hand_off_restore`) is
+    unit-tested; only the physical effect is unobserved.
+  - **wlroots group-aware exclusive** stays deferred: wlroots `exclusive` is not implemented at all (needs
+    a Sway box), so there is no topology to make group-aware yet. §6A multi-view on wlroots already works
+    (independent `HEADLESS-N` outputs).
+  - **Mutter `APPLY_TEMPORARY` disconnect-revert** (§7): when the FIRST Mutter session leaves under a live
+    sibling, Mutter reverts the topology — a full fix needs a group-owned `DisplayConfig` connection.
+- **Stage 6 — §6B protocol + Linux host + GTK client.** `VIDEO_CAP_MULTI_DISPLAY`, control-
+  stream Add/Remove/DisplayAdded, per-flow nonce-salt derivation, per-display pipelines on
+  KWin/wlroots, input display-index routing, C ABI additions, GTK client multi-window
+  presenter, stats display dimension.
+  *Validate:* loopback probe requesting 2 displays → two decodable .h265 outs + per-display
+  0xCF; then a real dual-monitor Linux client against the KDE box.
+- **Stage 7 — Windows multi-monitor** (§6.6: driver proto v3 per-monitor sealed rings, manager
+  slot map, Windows client multi-window, `separate` un-gated on Windows) — gated on driver CI +
+  on-glass, deliberately last.
+- **Stage 8 — polish.** Docs page finalized with real console screenshots, tray count/release
+  (stretch), README/CLAUDE.md/host.env.example updates, `local/summary` count, macOS §6B
+  presenter (its own mini-stage when scheduled).
+
+## 12. Risks & open questions
+
+- **PipeWire node reuse after consumer detach (KWin/Mutter)** — the load-bearing unknown for
+  Stage 2. If a kept node won't renegotiate for a fresh consumer, keep-alive on those backends
+  degrades to "topology-stable but recreate-on-reconnect" (still valuable: no desktop reshuffle
+  when *paired with identity naming*). The fallback is designed in, so the stage can't strand.
+- **KWin persistence of `Virtual-*` output config** — if KWin declines to persist virtual
+  outputs, per-client scaling on KDE needs punktfunk-side scale storage instead (the
+  `default_scale` adjunct already gives us the mechanism); identity naming stays worthwhile for
+  the name-clash fix alone.
+- **KWin stored-mode vs requested-mode fights** under identity naming (§5.4) — mitigated by
+  our post-create mode apply + read-back; watch for it in Stage 3 validation.
+- **Compositor ceilings on simultaneous virtual outputs** — load-bearing for §6A/§6B: probe
+  KWin's virtual-output count and Mutter's `RecordVirtual` count (≥2 monitors) empirically in
+  Stage 2/5; `max_displays` default 4 keeps us under any realistic ceiling.
+- **Encoder session exhaustion** (§6.4) — NVENC caps × split-encode × concurrent sessions must
+  be budgeted in one place (the admission check), or a second display can silently break an
+  unrelated session's encode. Split-encode is disabled for multi-display sessions by design.
+- **Per-display input mapping** — each Linux injector (libei, wlr, gamescope EIS) binds
+  absolute coordinates differently; the §6B display-index routing is per-injector work with
+  per-backend validation, not one generic patch.
+- **Client-side multi-window fullscreen juggling** (§6.5) — per-monitor DPI on Windows, Spaces
+  on macOS, pointer capture across our own windows; the reason clients stage GTK/Windows first.
+- **Idle kept displays burn resources** — a kept gamescope keeps the game rendering (GPU) at
+  full rate; a kept KWin output keeps compositing; every §6B display encodes at full rate.
+  Document; a later refinement could drop a kept session's refresh, out of scope here.
+- **Security posture** — keep-alive keeps a user session composited/running unattended;
+  nothing is unlocked that wasn't, and admission still rides pairing. `steal` on `--open`
+  hosts is the one sharp edge → docs recommend `reject` there (§5.3). The mgmt endpoints are
+  bearer-only; `local/summary` exposes counts only. §6B's extra UDP flows reuse the hardened
+  core `Session` unchanged (per-flow salts derived, never reused) — no new crypto surface.
+- **Mutter identity** — blocked on GNOME API surface; re-check per GNOME release.

docs-site/content/docs/configuration.md

@@ -62,9 +62,15 @@ picture.
 
 ## Compositor-specific (Linux)
 
+> **Managing virtual displays** — keep-alive after disconnect, exclusive vs. extend, and (on
+> Windows/KDE) persistent per-client scaling — now has its own settings surface in the web console
+> and `display-settings.json`. See [Virtual displays](/docs/virtual-displays). The two
+> `*_VIRTUAL_PRIMARY` knobs and `PUNKTFUNK_MONITOR_LINGER_MS` below still work but are superseded by
+> it (a settings file wins over them).
+
 | Setting | Values | Meaning |
 |---|---|---|
-| `PUNKTFUNK_KWIN_VIRTUAL_PRIMARY` | `1` | Make the streamed per-session output the sole desktop so plasmashell + windows render on it (not on the headless bootstrap output). Set by the KDE appliance `host.env`. |
+| `PUNKTFUNK_KWIN_VIRTUAL_PRIMARY` | `1` | Make the streamed per-session output the sole desktop so plasmashell + windows render on it (not on the headless bootstrap output). Set by the KDE appliance `host.env`. Superseded by the console's **Topology** setting. |
 | `PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY` | `1` | GNOME/Mutter equivalent of the above. |
 | `PUNKTFUNK_MUTTER_VIRTUAL_REFRESH` | `1` | Pin the client's exact WxH**@Hz** via `RecordVirtual`'s custom modes (needed for >60 Hz on Mutter). |
 
@@ -99,7 +105,7 @@ picture.
 |---|---|---|
 | `PUNKTFUNK_VDISPLAY` | `pf` | Virtual-display backend. The bundled pf-vdisplay IddCx driver is the only backend now — informational; leave as `pf`. |
 | `PUNKTFUNK_SECURE_DDA` | `1` | Capture the secure desktop (UAC / lock / login) so the stream survives those transitions. |
-| `PUNKTFUNK_MONITOR_LINGER_MS` | ms (default `10000`) | Defer tearing a per-client virtual display down after disconnect. A reconnect inside the window preempts it and creates a fresh one (a reused IddCx swap-chain is dead); the stable per-client monitor id keeps Windows' saved display config applying either way. |
+| `PUNKTFUNK_MONITOR_LINGER_MS` | ms (default `10000`) | Defer tearing a per-client virtual display down after disconnect. A reconnect inside the window preempts it and creates a fresh one (a reused IddCx swap-chain is dead); the stable per-client monitor id keeps Windows' saved display config applying either way. Superseded by the console's **Keep alive** setting — see [Virtual displays](/docs/virtual-displays). |
 | `PUNKTFUNK_RENDER_ADAPTER` | description substring | Multi-GPU boxes only: force the NVENC/capture GPU by adapter Description substring (e.g. `4090`). Leave unset on single-GPU machines. |
 | `PUNKTFUNK_HOST_CMD` | e.g. `serve --gamestream` | The host subcommand the service launches. Default `serve --gamestream`; use `serve` for a secure native-only host. |
 

docs-site/content/docs/meta.json

@@ -24,6 +24,7 @@
     "pairing",
     "---Configuration---",
     "configuration",
+    "virtual-displays",
     "host-cli",
     "---Troubleshooting---",
     "troubleshooting",

docs-site/content/docs/troubleshooting.md

@@ -10,11 +10,52 @@ description: Common problems setting up or using a punktfunk host, and how to fi
 - Host and client must be on the **same network/subnet**. Discovery uses mDNS, which doesn't cross
   routed subnets or most VPNs-without-multicast. As a fallback, add the host by **IP address** in your
   client.
-- A firewall on the host can block it. The native protocol's control plane uses UDP port **9777**. The
+- A firewall on the host can block it. The native protocol's **control plane** is a fixed UDP port,
-  per-session **data plane** uses an *ephemeral* UDP port negotiated at connect time (currently
+  **9777** — open this one. The per-session **data plane** rides a *separate, random* UDP port and
-  random) — for a strict firewall, open a UDP range or move the data port. GameStream/Moonlight uses
+  usually needs **no** firewall rule (see [Video is slow to start, or fails across
-  TCP **47984/47989/48010** + UDP **47998–48010** + ENet UDP **47999**. Allow them on the host's
+  subnets](#video-is-slow-to-start-or-fails-across-subnets) for why, and the one case where opening it
-  firewall.
+  helps). GameStream/Moonlight (only with `--gamestream`) uses TCP **47984/47989/48010** + UDP
+  **47998–48010** (video/FEC 47998, ENet control 47999, audio 48000) + mDNS UDP **5353**. Allow those
+  on the host's firewall.
+
+## Video is slow to start, or fails across subnets
+
+The native **data plane** (the raw UDP that carries video, separate from the 9777 control plane) uses
+a **random, per-session UDP port** — the host binds `0.0.0.0:0`, then tells the client which port it
+got during the connect handshake. There is no fixed data port.
+
+Video flows host → client, but the **client sends the first packet**: a small *hole-punch* datagram to
+that port. This is deliberate. It lets the host learn the client's real (possibly NAT-translated)
+source address and stream back to it, so a session can cross a NAT or a stateful inter-VLAN firewall
+**without** a forwarded data port. What it means for a host firewall:
+
+- **Same LAN, no host firewall (or the port allowed):** the punch arrives immediately and video starts
+  at once. Nothing to configure.
+- **Same LAN, host firewall that denies inbound** (ufw/nftables/firewalld default): the punch is
+  dropped, so the host waits **~2.5 s**, then falls back to the address the client reported and streams
+  anyway — a stateful firewall admits the return traffic because the host sent first. **Net effect: it
+  works, but each session takes ~2.5 s longer to start.** That slow start is the symptom of a
+  data-plane rule you're missing.
+- **Across subnets / NAT:** the same punch-then-fallback applies, as long as the host's outbound video
+  can reach the client (the path's stateful firewall then admits the return). If the host itself is
+  behind NAT reached only via a forwarded control port, the data path may not establish — this is the
+  case a fixed, forwardable data port would solve.
+
+To remove the ~2.5 s fallback delay, **pin the data port** with `--data-port` (or the
+`PUNKTFUNK_DATA_PORT` env in `host.env`) and open exactly that one port. The host then binds that
+fixed port, skips the punch-wait, and streams straight to the client — no timeout to pay:
+
+```sh
+punktfunk-host serve --data-port 9778     # or PUNKTFUNK_DATA_PORT=9778 in host.env
+sudo ufw allow 9778/udp                    # open exactly that one port
+```
+
+Two caveats. A fixed data port serves **one session at a time**; a second concurrent session finds it
+busy and transparently falls back to a random port + hole-punch (logged). And `--data-port` streams
+to the client's *reported* address, so use it only where that address is reachable — a flat LAN, or a
+port-forward that doesn't remap the client's source. Leave it **off** (the default) to keep the
+NAT-crossing hole-punch. On a normal single-LAN setup you can also just leave the data port closed and
+accept the one-time ~2.5 s punch-timeout, or not run a host firewall on a trusted LAN at all.
 
 ## `nvidia-smi` says it can't communicate with the driver
 

docs-site/content/docs/virtual-displays.md

@@ -0,0 +1,151 @@
+---
+title: Virtual displays
+description: Control how punktfunk creates, keeps alive, and arranges the virtual displays it streams — presets, keep-alive, exclusive vs. extend, and persistent per-client scaling.
+---
+
+When a client connects, punktfunk creates a **virtual display** sized to exactly that client's
+resolution and refresh, renders your desktop or game onto it, and streams it. This page is about the
+**policy** for that display: how long it survives a disconnect, whether it takes over your physical
+monitors, what happens when a second client connects, and how desktop environments remember
+per-client settings like scaling.
+
+You set this policy in the **web console** (Host → *Virtual displays*), or by editing
+`~/.config/punktfunk/display-settings.json` directly (`%ProgramData%\punktfunk\display-settings.json`
+on Windows). A change applies to the **next** connection — a running session keeps the display it
+opened on.
+
+> **You rarely need to touch this.** The default behavior matches how punktfunk has always worked.
+> Reach for a preset when you want a specific experience — a dedicated couch/gaming box, a desktop
+> you also use in person, or a multi-monitor workstation.
+
+> **What's live today:** **keep-alive** (linger, or **forever**), **topology** (extend / primary /
+> exclusive), **conflict handling**, **per-client identity + persistent scaling** (Windows *and*
+> KDE/KWin), and **multi-monitor layout** (several clients as monitors of one desktop) are all
+> enforced. A reconnect always resumes the kept display — even a fast one — instead of spawning a
+> second. The remaining gaps are noted inline: the Linux `primary` physical-keep *effect*, Sway
+> `exclusive`, and multi-display for a *single* client (that last is the next stage).
+
+## Pick a preset
+
+A preset is the easy way in — select one in the console and you're done. Each expands to a bundle of
+the individual options documented further down.
+
+| Preset | What it's for |
+|---|---|
+| **Default** | Today's behavior. A short linger absorbs reconnects, the streamed output becomes the sole desktop, and extra clients each get their own view. |
+| **Gaming rig** | A dedicated couch/headless box. The game and its display survive disconnects indefinitely (keep-alive **forever**), and whoever connects takes the box over. Release it from the console when you're done. |
+| **Shared desktop** | A desktop you also use in person. punktfunk never blanks your real monitors and never leaves a ghost display behind; concurrent viewers each get a view. |
+| **Hot-desk** | One user at a time with fast reattach — roaming between your own devices. A second user is told the box is busy, and each device+resolution keeps its own scaling. |
+| **Workstation** | The multi-monitor daily driver. Your displays come back exactly where you arranged them, with per-client identity and an exclusive desktop. |
+
+## Options reference
+
+Choose **Custom** in the console to set these directly.
+
+### Keep alive
+
+How long the virtual display survives after your last session disconnects. On a gamescope game host,
+this also keeps the **game itself running** so you can reconnect straight back into it.
+
+- **Off** — tear the display down at session end (nothing lingers).
+- **A duration** (seconds) — keep it for that long; a reconnect inside the window drops you straight
+  back in, with no re-negotiation and no desktop reshuffle.
+- **Forever** — keep it until you stop the host or **release it** from the console (Host → *Virtual
+  displays* → *Release*). This is the gaming-rig model.
+
+Default: **10 seconds**. Windows has always lingered 10 s; the Linux backends previously tore down
+immediately — a short linger makes reconnects smoother on both.
+
+**A reconnect always resumes the kept display** — the host recognises your device and hands back the
+same display, even if you reconnect a second or two after dropping (before it has noticed you left).
+**Deliberately quitting** (closing the client, not a network drop) tears the display down at once,
+skipping the linger, so you don't leave a ghost behind. How quickly a *dropped* client is noticed is
+the QUIC idle timeout — 8 s by default, tunable with `PUNKTFUNK_IDLE_TIMEOUT_MS` (see
+[Legacy environment knobs](#legacy-environment-knobs)) if you want kept displays freed sooner.
+
+> **Keep-alive + Exclusive keeps your physical monitors dark after you disconnect**, until the
+> linger expires or you release the display. That's intentional for a dedicated gaming box, but
+> don't set a long/forever keep-alive together with Exclusive on a machine whose monitors you also
+> use in person — use **Shared desktop** there instead.
+
+### Topology
+
+What punktfunk does with your monitor layout while it streams.
+
+- **Extend** — add the virtual display alongside your real monitors; touch nothing else.
+- **Primary** — make the virtual display your primary output; your physical monitors stay on.
+- **Exclusive** — the virtual display becomes your **only** enabled output (physical monitors are
+  disabled, then restored when streaming ends). This is what makes the streamed surface *be* the
+  desktop, so panels and windows land on it.
+- **Automatic** *(default)* — Exclusive on Windows and on an auto-detected KDE/GNOME desktop
+  ("stream this desktop" means the streamed output *is* the desktop); Extend when you've pinned a
+  specific compositor with `PUNKTFUNK_COMPOSITOR` (a test/CI posture).
+
+Per-backend support:
+
+| | KWin | Mutter/GNOME | Sway/wlroots | Windows |
+|---|---|---|---|---|
+| Extend | ✅ | ✅ | ✅ | ✅ |
+| Primary | ✅ | ✅ | ⚠️ treated as Extend | ✅ |
+| Exclusive | ✅ | ✅ | ⏳ following release | ✅ |
+
+### Conflict handling · identity · layout
+
+- **Conflict handling** — what happens when a *different* client connects while one is already
+  streaming and asks for a different resolution: give it its own display (**separate**), take the
+  box over (**steal**), share the existing display at its current mode (**join**), or refuse it
+  (**reject**). On Linux, `separate` gives each client its own display on the shared desktop. On
+  **Windows** a second client is **rejected** (a clean "host busy") even under `separate` — two
+  clients can't yet share one virtual display's capture there (that's a later stage), so the live
+  session is protected instead. A same-client *reconnect* never conflicts — it resumes.
+- **Identity** — whether each client gets a **stable display identity** so your desktop environment
+  remembers its settings (see [Persistent scaling](#persistent-scaling)): one shared identity, one
+  **per client**, or one **per client + resolution**.
+- **Layout / max displays** — when several clients each become a monitor of one desktop, this places
+  them side by side (**auto**) or exactly where you arrange them in the console (**manual**, keyed to
+  each client), up to **max displays**. Arrange them under Host → *Virtual displays* once two or more
+  are streaming.
+
+## Persistent scaling
+
+Set your display **scaling** once and have it stick across reconnects. This works by giving each
+client a *stable display identity*, so your desktop environment keys its per-monitor settings to it.
+
+| Host | Supported | How |
+|---|---|---|
+| **Windows** | ✅ today | Connect, set scaling in Settings while streaming — Windows remembers it per client. |
+| **KDE / KWin** | ✅ today | Set scaling in System Settings while streaming; KWin keys it to a stable per-client output name and reapplies it on reconnect. Validated live (150 %/125 % survive a full disconnect + reconnect). |
+| **GNOME / Mutter** | ❌ | GNOME's virtual-monitor API exposes no stable identity to key config on. |
+| **Sway / wlroots** | ❌ | Headless outputs can't carry a stable identity; pin scale in your sway config instead. |
+
+## Legacy environment knobs
+
+These `PUNKTFUNK_*` variables still work, but the console (and `display-settings.json`) supersede
+them — when a settings file exists, it wins.
+
+| Legacy knob | Now expressed as |
+|---|---|
+| `PUNKTFUNK_MONITOR_LINGER_MS` | **Keep alive** → duration *(Windows)* |
+| `PUNKTFUNK_NO_ISOLATE` | **Topology** → Extend *(Windows)* |
+| `PUNKTFUNK_KWIN_VIRTUAL_PRIMARY` / `PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY` | **Topology** → Exclusive (when set) / Extend (when `0`) |
+
+One knob has no console equivalent — it's a transport tuning, not display policy:
+
+- **`PUNKTFUNK_IDLE_TIMEOUT_MS`** (host, default `8000`) — how long the host waits before declaring a
+  *dropped* client gone, which is when a kept display starts its linger (or is freed). Lower it (e.g.
+  `3000`) to reclaim kept displays sooner after an ungraceful drop; it's clamped to ≥1 s and its
+  keep-alive ping scales with it, so a live session never false-disconnects. A deliberate quit is
+  instant regardless. Also `--idle-timeout-ms` on `punktfunk1-host`.
+
+## Troubleshooting
+
+**My physical monitors stayed off after I disconnected.** You have keep-alive set together with
+Exclusive topology — the display (and your isolated desktop) is being kept for the linger window.
+Release it from the console (Host → *Virtual displays*), or switch to the **Shared desktop** preset
+so streaming never disables your real monitors.
+
+**The virtual output shows only my wallpaper.** Your topology is Extend, so the streamed display is
+an empty extension. Use **Primary** or **Exclusive** so your desktop actually lands on it.
+
+**KWin virtual outputs need KWin ≥ 6.5.6.** Older KWin can't create the virtual output at all —
+see [requirements](/docs/requirements).

include/punktfunk_core.h

@@ -274,6 +274,15 @@
 #define VIDEO_CAP_HOST_TIMING 8
 #endif
 
+#if defined(PUNKTFUNK_FEATURE_QUIC)
+// QUIC application error code a punktfunk/1 client closes the control connection with on a
+// **deliberate quit** (a user "stop", not a network drop). The host reads it off the connection's
+// `ApplicationClosed` reason and tears the session's virtual display down immediately, skipping the
+// keep-alive linger; any other close reason (idle timeout, reset, a bare code 0) still lingers so a
+// reconnect can resume. Shared so host + every client agree on the code.
+#define QUIT_CLOSE_CODE 81
+#endif
+
 #if defined(PUNKTFUNK_FEATURE_QUIC)
 // [`Hello::video_codecs`] bit: the client can decode H.264 / AVC. The GPU-less **software**
 // encode path (openh264) emits H.264, so a client that wants to stream from a software host MUST

packaging/arch/README.md

@@ -176,8 +176,16 @@ Prefer explicit rules (or a firewall the shipped profiles don't cover)? Open the
 The **native `punktfunk/1`** plane:
 
 - **QUIC control plane: UDP 9777** (`serve --native-port N` to change).
-- **Data plane: an *ephemeral* UDP port** the client hole-punches — nothing to open inbound as long
+- **Data plane: a separate UDP port.** By default it's *random* — the host binds `0.0.0.0:0` and
-  as outbound UDP is allowed (the host streams back out through the client-opened path).
+  tells the client which port it got. Video flows host → client, but the **client sends the first
+  packet** (a hole-punch), so the host learns the client's real source and streams back — this
+  traverses NAT / inter-VLAN with no forwarded port. **You normally don't open it:** if a deny-inbound
+  firewall drops the punch, the host waits ~2.5 s and falls back to the client-reported address, and a
+  stateful firewall then admits the return (it just adds ~2.5 s to session start). To skip that delay,
+  pin it with **`serve --data-port <PORT>`** (or `PUNKTFUNK_DATA_PORT`): the host binds that fixed
+  port and streams direct (no punch-wait) — open exactly that one port. A fixed port serves one
+  session at a time (concurrent ones fall back to random + hole-punch), and direct mode needs the
+  client's reported address to be reachable (flat LAN / a non-remapping port-forward).
 
 And the **GameStream / Moonlight** ports (fixed) — only needed if you run the host with
 `serve --gamestream` (opt-in, trusted LAN only); bare `serve` is native-only and doesn't open these:
@@ -200,7 +208,9 @@ sudo ufw allow 9777/udp                                 # punktfunk/1 control pl
 sudo ufw allow 47984/tcp && sudo ufw allow 47989/tcp && sudo ufw allow 48010/tcp
 sudo ufw allow 47998,47999,48000/udp                    # GameStream video/control/audio
 sudo ufw allow 5353/udp                                 # mDNS discovery
-# The punktfunk/1 data plane is an ephemeral UDP port the host hole-punches — nothing to open here.
+# The punktfunk/1 data plane uses a random UDP port; leave it closed on a LAN — the host hole-punches
+# and falls back (~2.5s at session start if firewalled). To skip that, pin it: `serve --data-port
+# 9778` and `ufw allow 9778/udp`.
 ```
 
 With raw `nftables` (add to your `inet filter input` chain):
@@ -209,8 +219,8 @@ With raw `nftables` (add to your `inet filter input` chain):
 udp dport 9777 accept                  # punktfunk/1 control plane
 tcp dport { 47984, 47989, 48010 } accept
 udp dport { 47998-48000, 5353 } accept # GameStream video/control/audio + mDNS
-# The punktfunk/1 data plane is an ephemeral UDP port the host hole-punches — a stateful chain that
+# The punktfunk/1 data plane is a random UDP port — normally left closed (hole-punch + ~2.5s
-# accepts ct state established,related (as this one should) passes the return with nothing extra.
+# fallback). Pin it with `serve --data-port <PORT>` to open exactly one instead.
 ```
 
 ## Files

packaging/bazzite/README.md

@@ -374,9 +374,14 @@ sudo firewall-cmd --reload
 default unit):
 
 - **QUIC control plane: UDP 9777** (default `--port`; change with `--port N`).
-- **Data plane: an *ephemeral* UDP port** — `punktfunk1-host` binds `0.0.0.0:0` and tells the client which
+- **Data plane: a separate UDP port** — by default *random* (`0.0.0.0:0`), so there is **no fixed
-  port it got, so there is **no fixed data port to open**. For a restrictive firewall you'd need to
+  port to open**. Video flows host → client, but the client sends the first packet (a hole-punch): if
-  allow the ephemeral UDP range; the repo does not pin one.
+  firewalld drops it, the host waits ~2.5 s and falls back to the client-reported address and streams
+  anyway, so you normally **leave the data port closed**. To skip that ~2.5 s fallback, pin it with
+  `serve --data-port <PORT>` (or `PUNKTFUNK_DATA_PORT`) and open exactly that one port with
+  `firewall-cmd --add-port=<PORT>/udp`. A fixed port serves one session at a time (concurrent ones
+  fall back to random + hole-punch) and streams to the client's reported address (flat LAN /
+  non-remapping forward only).
 
 ```sh
 # Only if you run `punktfunk1-host`:

packaging/debian/README.md

@@ -76,8 +76,16 @@ open its port with the matching one-liner — `sudo ufw allow punktfunk-web` or
 Prefer explicit rules? Open the ports directly. The **native `punktfunk/1`** plane:
 
 - **QUIC control plane: UDP 9777** (`serve --native-port N` to change).
-- **Data plane: an *ephemeral* UDP port** the client hole-punches — nothing to open inbound as long
+- **Data plane: a separate UDP port.** By default it's *random* — the host binds `0.0.0.0:0` and
-  as outbound UDP is allowed (the host streams back out through the client-opened path).
+  tells the client which port it got. Video flows host → client, but the **client sends the first
+  packet** (a hole-punch), so the host learns the client's real source and streams back — this
+  traverses NAT / inter-VLAN with no forwarded port. **You normally don't open it:** if a deny-inbound
+  firewall drops the punch, the host waits ~2.5 s and falls back to the client-reported address, and a
+  stateful firewall then admits the return (it just adds ~2.5 s to session start). To skip that delay,
+  pin it with **`serve --data-port <PORT>`** (or `PUNKTFUNK_DATA_PORT`): the host binds that fixed
+  port and streams direct (no punch-wait) — open exactly that one port. A fixed port serves one
+  session at a time (concurrent ones fall back to random + hole-punch), and direct mode needs the
+  client's reported address to be reachable (flat LAN / a non-remapping port-forward).
 
 And the **GameStream / Moonlight** ports (fixed) — only needed if you run the host with
 `serve --gamestream` (opt-in, trusted LAN only); bare `serve` is native-only and doesn't open these:
@@ -100,7 +108,9 @@ sudo ufw allow 9777/udp                                 # punktfunk/1 control pl
 sudo ufw allow 47984/tcp && sudo ufw allow 47989/tcp && sudo ufw allow 48010/tcp
 sudo ufw allow 47998,47999,48000/udp                    # GameStream video/control/audio
 sudo ufw allow 5353/udp                                 # mDNS discovery
-# The punktfunk/1 data plane is an ephemeral UDP port the host hole-punches — nothing to open here.
+# The punktfunk/1 data plane uses a random UDP port; leave it closed on a LAN — the host hole-punches
+# and falls back (~2.5s at session start if firewalled). To skip that, pin it: `serve --data-port
+# 9778` and `ufw allow 9778/udp`.
 ```
 
 With raw `nftables` (add to your `inet filter input` chain):
@@ -109,7 +119,8 @@ With raw `nftables` (add to your `inet filter input` chain):
 udp dport 9777 accept                  # punktfunk/1 control plane
 tcp dport { 47984, 47989, 48010 } accept
 udp dport { 47998-48010, 5353 } accept
-# plus the ephemeral punktfunk/1 data port (a reserved UDP range).
+# The punktfunk/1 data plane is a random UDP port — normally left closed (hole-punch + ~2.5s
+# fallback). Pin it with `serve --data-port <PORT>` to open exactly one instead.
 ```
 
 ## Updates

scripts/host.env.example

@@ -48,6 +48,15 @@ PUNKTFUNK_ZEROCOPY=1
 #PUNKTFUNK_INPUT_BACKEND=libei      # wlr | libei | gamescope | uinput
 #PUNKTFUNK_FEC_PCT=20               # video FEC overhead percent
 #PUNKTFUNK_PERF=1                   # per-stage timing logs
+# Display-management policy (keep-alive · topology · conflict · identity · layout · max) is set in the
+# web console (Host → Virtual displays) → ~/.config/punktfunk/display-settings.json, NOT here; a
+# settings file supersedes the legacy PUNKTFUNK_MONITOR_LINGER_MS / _NO_ISOLATE / *_VIRTUAL_PRIMARY
+# knobs. One transport knob has no console equivalent:
+#PUNKTFUNK_IDLE_TIMEOUT_MS=8000     # disconnect-detection latency: how long before a DROPPED client is
+                                    # declared gone (a kept display then starts its linger, or frees).
+                                    # Lower (e.g. 3000) to reclaim kept displays sooner after an
+                                    # ungraceful drop; clamped ≥1s, keep-alive ping scales with it so a
+                                    # live session never false-disconnects. A deliberate quit is instant.
 # Full-chroma 4:4:4 (HEVC Range Extensions) — sharper text/desktop, no chroma loss. Honored only on
 # the punktfunk/1 native path when the client advertises 4:4:4 AND the GPU supports it (probed; else
 # the session stays 4:2:0). HEVC-only; independent of 10-bit. NVENC (NVIDIA) is the validated path;

web/messages/de.json

@@ -4,6 +4,7 @@
 	"app_tagline": "Verwaltungskonsole",
 	"nav_dashboard": "Übersicht",
 	"nav_host": "Host",
+	"nav_displays": "Virtuelle Anzeigen",
 	"nav_clients": "Gekoppelte Geräte",
 	"nav_pairing": "Kopplung",
 	"nav_library": "Bibliothek",
@@ -47,6 +48,61 @@
 	"gpu_none": "Keine GPUs erkannt.",
 	"gpu_missing_warning": "Die bevorzugte GPU „{name}“ ist nicht vorhanden — stattdessen wird automatisch gewählt.",
 	"gpu_env_note": "PUNKTFUNK_RENDER_ADAPTER={value} bindet die GPU im Automatikmodus.",
+	"host_displays": "Virtuelle Displays",
+	"host_displays_help": "Wie virtuelle Displays erstellt, aktiv gehalten und angeordnet werden. Wähle eine Voreinstellung oder „Benutzerdefiniert“, um Optionen direkt zu setzen. Eine Änderung gilt ab der nächsten Sitzung.",
+	"display_config_title": "Konfiguration",
+	"display_preset": "Voreinstellung",
+	"display_preset_custom": "Benutzerdefiniert",
+	"display_preset_default": "Standard",
+	"display_preset_gaming_rig": "Gaming-Rig",
+	"display_preset_shared_desktop": "Geteilter Desktop",
+	"display_preset_hotdesk": "Hot-Desk",
+	"display_preset_workstation": "Workstation",
+	"display_keep_alive": "Nach Trennung aktiv halten",
+	"display_keep_alive_off": "Aus",
+	"display_keep_alive_keep": "Behalten für",
+	"display_keep_alive_seconds": "Sekunden",
+	"display_topology": "Topologie",
+	"display_topology_auto": "Automatisch",
+	"display_topology_extend": "Erweitern",
+	"display_topology_primary": "Primär",
+	"display_topology_exclusive": "Exklusiv",
+	"display_max": "Max. Displays",
+	"display_save": "Speichern",
+	"display_effective": "Aktiv",
+	"display_pending_note": "Änderungen greifen ab der nächsten Verbindung — eine laufende Sitzung behält die Anzeige, mit der sie gestartet ist.",
+	"display_live": "Aktive Displays",
+	"display_none_live": "Derzeit keine virtuellen Displays.",
+	"display_state_active": "Aktiv",
+	"display_state_lingering": "Wird gehalten",
+	"display_state_pinned": "Angeheftet",
+	"display_release_btn": "Freigeben",
+	"display_release_all": "Alle gehaltenen freigeben",
+	"display_expires_in": "Abbau in {sec}s",
+	"display_sessions": "{count} streamend",
+	"display_arrange": "Anzeigen anordnen",
+	"display_arrange_help": "Legen Sie fest, wo jede gestreamte Anzeige auf dem Desktop sitzt (in Pixeln). Beim Speichern wird auf ein manuelles Layout umgeschaltet; es greift ab der nächsten Verbindung.",
+	"display_arrange_save": "Anordnung speichern",
+	"display_custom_desc": "Jede Option selbst festlegen.",
+	"display_preset_current": "Aktiv",
+	"display_preset_soon": "in Kürze",
+	"display_keep_alive_help": "„Aus“ baut die Anzeige sofort beim Trennen ab. Halte sie (und bei gamescope ihr Spiel) am Leben, damit ein schnelles Wiederverbinden sofort fortsetzt, statt neu aufzubauen.",
+	"display_topology_help": "Was mit den physischen Monitoren des Hosts während des Streamings geschieht.",
+	"display_conflict": "Wenn ein weiterer Client verbindet",
+	"display_conflict_help": "Was passiert, wenn ein zweiter Client verbindet, während bereits gestreamt wird, und eine andere Auflösung anfragt.",
+	"display_conflict_separate": "Eigene Anzeige",
+	"display_conflict_steal": "Übernehmen",
+	"display_conflict_join": "Ansicht teilen",
+	"display_conflict_reject": "Besetzt — ablehnen",
+	"display_identity": "Client-Identität",
+	"display_identity_help": "Jedem Client eine stabile Anzeige geben, damit der Desktop seine Monitor-Einstellungen merkt (z. B. Skalierung).",
+	"display_identity_shared": "Geteilt",
+	"display_identity_per_client": "Pro Client",
+	"display_identity_per_client_mode": "Pro Client + Auflösung",
+	"display_layout_mode": "Multi-Monitor-Anordnung",
+	"display_layout_help": "Automatisch ordnet die Anzeigen nebeneinander an (links nach rechts). Manuell: Du platzierst jede selbst — ein X/Y-Editor pro Anzeige erscheint im Abschnitt „Aktive Displays“ unten, sobald zwei oder mehr streamen.",
+	"display_layout_auto_row": "Automatisch (nebeneinander)",
+	"display_layout_manual": "Manuell",
 	"clients_title": "Gekoppelte Geräte",
 	"clients_empty": "Noch keine gekoppelten Geräte.",
 	"clients_name": "Name",

web/messages/en.json

@@ -4,6 +4,7 @@
 	"app_tagline": "management console",
 	"nav_dashboard": "Dashboard",
 	"nav_host": "Host",
+	"nav_displays": "Virtual displays",
 	"nav_clients": "Paired clients",
 	"nav_pairing": "Pairing",
 	"nav_library": "Library",
@@ -47,6 +48,61 @@
 	"gpu_none": "No GPUs detected.",
 	"gpu_missing_warning": "The preferred GPU “{name}” is not present — automatic selection is used instead.",
 	"gpu_env_note": "PUNKTFUNK_RENDER_ADAPTER={value} pins the GPU while in automatic mode.",
+	"host_displays": "Virtual displays",
+	"host_displays_help": "How virtual displays are created, kept alive, and arranged. Pick a preset, or choose Custom to set options directly. A change applies to the next session.",
+	"display_config_title": "Configuration",
+	"display_preset": "Preset",
+	"display_preset_custom": "Custom",
+	"display_preset_default": "Default",
+	"display_preset_gaming_rig": "Gaming rig",
+	"display_preset_shared_desktop": "Shared desktop",
+	"display_preset_hotdesk": "Hot-desk",
+	"display_preset_workstation": "Workstation",
+	"display_keep_alive": "Keep alive after disconnect",
+	"display_keep_alive_off": "Off",
+	"display_keep_alive_keep": "Keep for",
+	"display_keep_alive_seconds": "seconds",
+	"display_topology": "Topology",
+	"display_topology_auto": "Automatic",
+	"display_topology_extend": "Extend",
+	"display_topology_primary": "Primary",
+	"display_topology_exclusive": "Exclusive",
+	"display_max": "Max displays",
+	"display_save": "Save",
+	"display_effective": "In effect",
+	"display_pending_note": "Changes apply from the next connection — a streaming session keeps the display it opened on.",
+	"display_live": "Live displays",
+	"display_none_live": "No virtual displays right now.",
+	"display_state_active": "Active",
+	"display_state_lingering": "Lingering",
+	"display_state_pinned": "Pinned",
+	"display_release_btn": "Release",
+	"display_release_all": "Release all kept",
+	"display_expires_in": "tears down in {sec}s",
+	"display_sessions": "{count} streaming",
+	"display_arrange": "Arrange displays",
+	"display_arrange_help": "Set where each streamed display sits on the desktop, in pixels. Saving switches to a manual layout; it applies from the next connect.",
+	"display_arrange_save": "Save arrangement",
+	"display_custom_desc": "Set every option yourself.",
+	"display_preset_current": "Active",
+	"display_preset_soon": "coming soon",
+	"display_keep_alive_help": "Off tears the display down as soon as the client disconnects. Keep it alive (and, on gamescope, its game) so a quick reconnect resumes instantly instead of rebuilding.",
+	"display_topology_help": "What happens to the host's physical monitors while streaming.",
+	"display_conflict": "When another client connects",
+	"display_conflict_help": "What happens if a second client connects while one is already streaming and asks for a different resolution.",
+	"display_conflict_separate": "Own display",
+	"display_conflict_steal": "Take over",
+	"display_conflict_join": "Share view",
+	"display_conflict_reject": "Busy — reject",
+	"display_identity": "Per-client identity",
+	"display_identity_help": "Give each client a stable display so the desktop remembers its per-monitor settings (e.g. scaling).",
+	"display_identity_shared": "Shared",
+	"display_identity_per_client": "Per client",
+	"display_identity_per_client_mode": "Per client + resolution",
+	"display_layout_mode": "Multi-monitor layout",
+	"display_layout_help": "Auto lays displays out side by side, left to right. Manual: you position each one yourself — a per-display X/Y editor appears in the Live displays section below once two or more are streaming.",
+	"display_layout_auto_row": "Auto (side by side)",
+	"display_layout_manual": "Manual",
 	"clients_title": "Paired clients",
 	"clients_empty": "No paired clients yet.",
 	"clients_name": "Name",

web/src/components/app-shell.tsx

@@ -4,6 +4,7 @@ import {
 	GaugeCircle,
 	KeyRound,
 	LibraryBig,
+	MonitorPlay,
 	ScrollText,
 	Server,
 	Settings,
@@ -21,6 +22,7 @@ const MLink = motion(Link);
 const NAV = [
 	{ to: "/", icon: Activity, label: () => m.nav_dashboard() },
 	{ to: "/host", icon: Server, label: () => m.nav_host() },
+	{ to: "/displays", icon: MonitorPlay, label: () => m.nav_displays() },
 	{ to: "/library", icon: LibraryBig, label: () => m.nav_library() },
 	{ to: "/stats", icon: GaugeCircle, label: () => m.nav_stats() },
 	{ to: "/logs", icon: ScrollText, label: () => m.nav_logs() },

web/src/routes/displays.tsx

@@ -0,0 +1,4 @@
+import { createFileRoute } from "@tanstack/react-router";
+import { SectionDisplays } from "@/sections/Displays";
+
+export const Route = createFileRoute("/displays")({ component: SectionDisplays });

web/src/sections/Displays/DisplayCard.tsx

@@ -0,0 +1,629 @@
+import { useQueryClient } from "@tanstack/react-query";
+import { Button } from "@unom/ui/button";
+import { type FC, type ReactNode, useEffect, useState } from "react";
+import {
+	getGetDisplayStateQueryKey,
+	getGetDisplaySettingsQueryKey,
+	useGetDisplaySettings,
+	useGetDisplayState,
+	useReleaseDisplay,
+	useSetDisplayLayout,
+	useSetDisplaySettings,
+} from "@/api/gen/display/display";
+import type {
+	ApiDisplayInfo,
+	DisplayPolicy,
+	EffectivePolicy,
+	Identity,
+	KeepAlive,
+	LayoutMode,
+	ModeConflict,
+	Preset,
+	Topology,
+} from "@/api/gen/model";
+import { ApiError } from "@/api/fetcher";
+import { QueryState } from "@/components/query-state";
+import { Badge } from "@/components/ui/badge";
+import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import { cn } from "@/lib/utils";
+import { m } from "@/paraglide/messages";
+
+/**
+ * Container: the host's virtual-display management policy (design/display-management.md). Lets the
+ * operator pick a one-click preset OR set every option by hand — all WITHOUT any client connected
+ * (this is the host's *next-connect* behavior). The live-display list + multi-monitor arrangement
+ * table below act on whatever is currently streaming.
+ */
+export const DisplaySection: FC = () => {
+	const qc = useQueryClient();
+	const q = useGetDisplaySettings();
+	const save = useSetDisplaySettings();
+
+	// Local edit buffer, seeded once from the server and re-seeded after every successful apply.
+	const [draft, setDraft] = useState<DisplayPolicy | null>(null);
+	useEffect(() => {
+		if (q.data && draft === null) setDraft(q.data.settings);
+	}, [q.data, draft]);
+
+	// Apply a policy (a one-click preset, or the hand-edited Custom draft). A change takes effect on
+	// the next connect; a live session keeps the display it opened on.
+	const apply = (policy: DisplayPolicy) =>
+		save.mutate(
+			{ data: policy },
+			{
+				onSuccess: (res) => {
+					setDraft(res.settings);
+					qc.invalidateQueries({ queryKey: getGetDisplaySettingsQueryKey() });
+				},
+			},
+		);
+
+	return (
+		<div className="flex flex-col gap-card">
+			<Card>
+				<CardHeader>
+					<CardTitle>{m.display_config_title()}</CardTitle>
+				</CardHeader>
+				<CardContent className="space-y-4">
+					<p className="text-sm text-muted-foreground">{m.host_displays_help()}</p>
+					<QueryState isLoading={q.isLoading} error={q.error} refetch={q.refetch}>
+						{q.data && draft && (
+							<DisplayForm
+								draft={draft}
+								setDraft={setDraft}
+								presets={q.data.presets}
+								apply={apply}
+								busy={save.isPending}
+								error={apiErrorMessage(save.error)}
+							/>
+						)}
+					</QueryState>
+				</CardContent>
+			</Card>
+			<Card>
+				<CardHeader>
+					<CardTitle>{m.display_live()}</CardTitle>
+				</CardHeader>
+				<CardContent>
+					<LiveDisplays />
+				</CardContent>
+			</Card>
+		</div>
+	);
+};
+
+/** Preset display order — Default first (the safe baseline), the situational ones, then Custom. */
+const PRESET_ORDER = [
+	"default",
+	"shared-desktop",
+	"hotdesk",
+	"workstation",
+	"gaming-rig",
+	"custom",
+] as const;
+
+const DisplayForm: FC<{
+	draft: DisplayPolicy;
+	setDraft: (p: DisplayPolicy) => void;
+	presets: { id: string; summary: string; fields: EffectivePolicy }[];
+	apply: (p: DisplayPolicy) => void;
+	busy: boolean;
+	error?: string;
+}> = ({ draft, setDraft, presets, apply, busy, error }) => {
+	const preset: Preset = draft.preset ?? "custom";
+	const isCustom = preset === "custom";
+
+	// The Custom fields (defaults filled): the edit buffer when preset === "custom", and what a
+	// preset→Custom switch is seeded from, so you customize starting from the current behavior.
+	const customFields: EffectivePolicy = {
+		keep_alive: draft.keep_alive ?? { mode: "duration", seconds: 10 },
+		topology: draft.topology ?? "auto",
+		mode_conflict: draft.mode_conflict ?? "separate",
+		identity: draft.identity ?? "per-client",
+		layout: draft.layout ?? { mode: "auto-row", positions: {} },
+		max_displays: draft.max_displays ?? 4,
+	};
+	const effective: EffectivePolicy =
+		(isCustom ? undefined : presets.find((p) => p.id === preset)?.fields) ?? customFields;
+
+	// The five named presets apply in ONE click; "Custom" reveals the fields, seeded from the current
+	// effective behavior (nothing changes until you Save).
+	const pickPreset = (id: string) => {
+		if (id === "custom") {
+			setDraft({
+				version: 1,
+				preset: "custom",
+				keep_alive: effective.keep_alive,
+				topology: effective.topology,
+				mode_conflict: effective.mode_conflict,
+				identity: effective.identity,
+				layout: effective.layout,
+				max_displays: effective.max_displays,
+			});
+		} else {
+			apply({ ...draft, preset: id as Preset });
+		}
+	};
+
+	const ka = customFields.keep_alive;
+	// The duration value, remembered across the Off/Keep toggle so switching back restores it.
+	const [keepSecs, setKeepSecs] = useState(ka.mode === "duration" ? ka.seconds : 300);
+
+	return (
+		<div className="space-y-6">
+			{/* One-click presets — a 2-up grid so each has room to breathe */}
+			<div className="space-y-3">
+				<Label className="text-base font-semibold">{m.display_preset()}</Label>
+				<div className="grid gap-3 sm:grid-cols-2">
+					{PRESET_ORDER.map((id) => {
+						const p = presets.find((x) => x.id === id);
+						const fields = id === "custom" ? undefined : p?.fields;
+						const summary = id === "custom" ? m.display_custom_desc() : p?.summary;
+						const selected = preset === id;
+						const soon = DISABLED_PRESETS.has(id);
+						const disabled = busy || soon;
+						const pick = () => {
+							if (!disabled) pickPreset(id);
+						};
+						return (
+							<Card
+								key={id}
+								interactive
+								role="button"
+								tabIndex={disabled ? -1 : 0}
+								aria-pressed={selected}
+								aria-disabled={disabled || undefined}
+								onClick={pick}
+								onKeyDown={(e) => {
+									if (e.key === "Enter" || e.key === " ") {
+										e.preventDefault();
+										pick();
+									}
+								}}
+								className={cn(
+									"flex h-full flex-col p-4",
+									disabled ? "cursor-not-allowed opacity-60" : "cursor-pointer",
+									selected && "ring-2 ring-primary",
+								)}
+							>
+								<div className="flex items-center justify-between gap-2">
+									<span className="text-base font-semibold">
+										{(PRESET_LABEL[id] ?? (() => id))()}
+										{soon && (
+											<span className="ml-2 text-xs font-normal text-muted-foreground">
+												{m.display_preset_soon()}
+											</span>
+										)}
+									</span>
+									{selected && (
+										<Badge variant="success">{m.display_preset_current()}</Badge>
+									)}
+								</div>
+								{summary && (
+									<p className="mt-1 text-sm text-muted-foreground">{summary}</p>
+								)}
+								{fields && (
+									<div className="mt-auto flex flex-wrap gap-1.5 pt-3">
+										<Badge variant="secondary">{fmtKeepAlive(fields.keep_alive)}</Badge>
+										<Badge variant="secondary">{tr(TOPOLOGY_LABEL, fields.topology)}</Badge>
+										<Badge variant="outline">{tr(CONFLICT_LABEL, fields.mode_conflict)}</Badge>
+										<Badge variant="outline">{tr(IDENTITY_LABEL, fields.identity)}</Badge>
+									</div>
+								)}
+							</Card>
+						);
+					})}
+				</div>
+			</div>
+
+			{/* Custom: every option by hand */}
+			{isCustom && (
+				<div className="space-y-6 rounded-lg border p-5">
+					<Field label={m.display_keep_alive()} help={m.display_keep_alive_help()}>
+						<div className="flex flex-wrap items-center gap-2">
+							<Button
+								size="sm"
+								variant={ka.mode === "off" ? "default" : "outline"}
+								disabled={busy}
+								onClick={() => setDraft({ ...draft, keep_alive: { mode: "off" } })}
+							>
+								{m.display_keep_alive_off()}
+							</Button>
+							<Button
+								size="sm"
+								variant={ka.mode === "duration" ? "default" : "outline"}
+								disabled={busy}
+								onClick={() =>
+									setDraft({ ...draft, keep_alive: { mode: "duration", seconds: keepSecs } })
+								}
+							>
+								{m.display_keep_alive_keep()}
+							</Button>
+							{ka.mode === "duration" && (
+								<div className="flex items-center gap-2">
+									<Input
+										type="number"
+										min={0}
+										className="w-24"
+										value={ka.seconds}
+										disabled={busy}
+										onChange={(e) => {
+											const n = Math.max(0, Number(e.target.value) || 0);
+											setKeepSecs(n);
+											setDraft({ ...draft, keep_alive: { mode: "duration", seconds: n } });
+										}}
+									/>
+									<span className="text-sm text-muted-foreground">
+										{m.display_keep_alive_seconds()}
+									</span>
+								</div>
+							)}
+						</div>
+					</Field>
+
+					<Choice
+						label={m.display_topology()}
+						help={m.display_topology_help()}
+						value={customFields.topology}
+						options={["auto", "extend", "primary", "exclusive"]}
+						labels={TOPOLOGY_LABEL}
+						disabled={busy}
+						onPick={(v) => setDraft({ ...draft, topology: v as Topology })}
+					/>
+					<Choice
+						label={m.display_conflict()}
+						help={m.display_conflict_help()}
+						value={customFields.mode_conflict}
+						options={["separate", "steal", "join", "reject"]}
+						labels={CONFLICT_LABEL}
+						disabled={busy}
+						onPick={(v) => setDraft({ ...draft, mode_conflict: v as ModeConflict })}
+					/>
+					<Choice
+						label={m.display_identity()}
+						help={m.display_identity_help()}
+						value={customFields.identity}
+						options={["shared", "per-client", "per-client-mode"]}
+						labels={IDENTITY_LABEL}
+						disabled={busy}
+						onPick={(v) => setDraft({ ...draft, identity: v as Identity })}
+					/>
+					<Choice
+						label={m.display_layout_mode()}
+						help={m.display_layout_help()}
+						value={customFields.layout.mode ?? "auto-row"}
+						options={["auto-row", "manual"]}
+						labels={LAYOUT_LABEL}
+						disabled={busy}
+						onPick={(v) =>
+							setDraft({
+								...draft,
+								layout: { mode: v as LayoutMode, positions: draft.layout?.positions ?? {} },
+							})
+						}
+					/>
+
+					<Field label={m.display_max()}>
+						<Input
+							type="number"
+							min={1}
+							max={16}
+							className="w-24"
+							value={draft.max_displays ?? 4}
+							disabled={busy}
+							onChange={(e) =>
+								setDraft({
+									...draft,
+									max_displays: Math.min(16, Math.max(1, Number(e.target.value) || 1)),
+								})
+							}
+						/>
+					</Field>
+
+					<div className="border-t pt-4">
+						<Button onClick={() => apply(draft)} disabled={busy}>
+							{m.display_save()}
+						</Button>
+					</div>
+				</div>
+			)}
+
+			{/* What's in force right now */}
+			<div className="flex flex-wrap items-center gap-2 border-t pt-3">
+				<span className="text-sm text-muted-foreground">{m.display_effective()}:</span>
+				<Badge variant="secondary">{fmtKeepAlive(effective.keep_alive)}</Badge>
+				<Badge variant="secondary">{tr(TOPOLOGY_LABEL, effective.topology)}</Badge>
+				<Badge variant="outline">{tr(CONFLICT_LABEL, effective.mode_conflict)}</Badge>
+				<Badge variant="outline">{tr(IDENTITY_LABEL, effective.identity)}</Badge>
+				<Badge variant="outline">{tr(LAYOUT_LABEL, effective.layout.mode)}</Badge>
+				<Badge variant="outline">{`${effective.max_displays}×`}</Badge>
+			</div>
+
+			<p className="text-xs text-muted-foreground">{m.display_pending_note()}</p>
+			{error && <p className="text-sm text-amber-600 dark:text-amber-500">{error}</p>}
+		</div>
+	);
+};
+
+/** A labeled config field — label, then the control, then optional help. The single source of the
+ * label→control→help spacing so every field (keep-alive, the button groups, max-displays) lines up. */
+const Field: FC<{ label: string; help?: string; children: ReactNode }> = ({
+	label,
+	help,
+	children,
+}) => (
+	<div className="space-y-3">
+		<Label className="block">{label}</Label>
+		{children}
+		{help && <p className="text-xs text-muted-foreground">{help}</p>}
+	</div>
+);
+
+/** A [`Field`] whose control is a row of mutually-exclusive option buttons (topology / conflict / …). */
+const Choice: FC<{
+	label: string;
+	help?: string;
+	value: string;
+	options: readonly string[];
+	labels: Record<string, () => string>;
+	disabled: boolean;
+	onPick: (v: string) => void;
+}> = ({ label, help, value, options, labels, disabled, onPick }) => (
+	<Field label={label} help={help}>
+		<div className="flex flex-wrap gap-2">
+			{options.map((o) => (
+				<Button
+					key={o}
+					size="sm"
+					variant={value === o ? "default" : "outline"}
+					disabled={disabled}
+					onClick={() => onPick(o)}
+				>
+					{(labels[o] ?? (() => o))()}
+				</Button>
+			))}
+		</div>
+	</Field>
+);
+
+/**
+ * The host's live/kept virtual displays, polled from `/display/state`, each with a Release button
+ * for lingering/pinned ones (active displays can't be released — that's session control).
+ */
+const LiveDisplays: FC = () => {
+	const qc = useQueryClient();
+	const state = useGetDisplayState({ query: { refetchInterval: 2_000 } });
+	const release = useReleaseDisplay();
+	const displays = state.data?.displays ?? [];
+	const kept = displays.filter((d) => d.state !== "active");
+
+	const doRelease = (slot?: number) =>
+		release.mutate(
+			{ data: { slot: slot ?? null } },
+			{ onSuccess: () => qc.invalidateQueries({ queryKey: getGetDisplayStateQueryKey() }) },
+		);
+
+	return (
+		<div className="space-y-3">
+			{kept.length > 0 && (
+				<div className="flex justify-end">
+					<Button
+						size="sm"
+						variant="outline"
+						disabled={release.isPending}
+						onClick={() => doRelease()}
+					>
+						{m.display_release_all()}
+					</Button>
+				</div>
+			)}
+			{displays.length === 0 ? (
+				<p className="text-sm text-muted-foreground">{m.display_none_live()}</p>
+			) : (
+				<ul className="divide-y rounded-md border">
+					{displays.map((d) => (
+						<DisplayRow
+							key={d.slot}
+							d={d}
+							busy={release.isPending}
+							onRelease={() => doRelease(d.slot)}
+						/>
+					))}
+				</ul>
+			)}
+			<DisplayArrangement displays={displays} />
+		</div>
+	);
+};
+
+/**
+ * The multi-monitor **arrangement** editor (design/display-management.md §6.2): an x/y table over the
+ * live displays that carry a stable identity slot (the manual-layout key). Saving writes
+ * `PUT /display/layout`, which switches the host to a manual layout and applies from the next connect.
+ * Shown only for a ≥2-display group — arranging a single display is moot.
+ */
+const DisplayArrangement: FC<{ displays: ApiDisplayInfo[] }> = ({ displays }) => {
+	const qc = useQueryClient();
+	const saveLayout = useSetDisplayLayout();
+	// Only displays with a stable identity slot can be pinned (shared/anonymous ones have no key).
+	const arrangeable = displays.filter((d) => d.identity_slot != null);
+
+	// Local edit buffer keyed by identity-slot string → {x, y}, seeded once from the current positions.
+	const [pos, setPos] = useState<Record<string, { x: number; y: number }> | null>(null);
+	useEffect(() => {
+		if (pos === null && arrangeable.length > 0) {
+			const seed: Record<string, { x: number; y: number }> = {};
+			for (const d of arrangeable) seed[String(d.identity_slot)] = { x: d.x, y: d.y };
+			setPos(seed);
+		}
+	}, [arrangeable, pos]);
+
+	if (arrangeable.length < 2) return null;
+	const cur = pos ?? {};
+
+	const setXY = (slot: number, key: "x" | "y", val: number) => {
+		const k = String(slot);
+		setPos({ ...cur, [k]: { ...(cur[k] ?? { x: 0, y: 0 }), [key]: val } });
+	};
+
+	const onSave = () =>
+		saveLayout.mutate(
+			{ data: { positions: cur } },
+			{ onSuccess: () => qc.invalidateQueries({ queryKey: getGetDisplayStateQueryKey() }) },
+		);
+
+	return (
+		<div className="space-y-2 border-t pt-4">
+			<h4 className="text-sm font-medium">{m.display_arrange()}</h4>
+			<p className="text-xs text-muted-foreground">{m.display_arrange_help()}</p>
+			<div className="space-y-2">
+				{arrangeable.map((d) => {
+					const slot = d.identity_slot as number;
+					const p = cur[String(slot)] ?? { x: d.x, y: d.y };
+					return (
+						<div key={d.slot} className="flex flex-wrap items-center gap-2 text-sm">
+							<span className="w-44 truncate">
+								{d.mode} <code className="text-xs text-muted-foreground">#{slot}</code>
+							</span>
+							<Label className="text-xs" htmlFor={`disp-x-${slot}`}>
+								X
+							</Label>
+							<Input
+								id={`disp-x-${slot}`}
+								type="number"
+								className="w-24"
+								value={p.x}
+								disabled={saveLayout.isPending}
+								onChange={(e) => setXY(slot, "x", Math.trunc(Number(e.target.value) || 0))}
+							/>
+							<Label className="text-xs" htmlFor={`disp-y-${slot}`}>
+								Y
+							</Label>
+							<Input
+								id={`disp-y-${slot}`}
+								type="number"
+								className="w-24"
+								value={p.y}
+								disabled={saveLayout.isPending}
+								onChange={(e) => setXY(slot, "y", Math.trunc(Number(e.target.value) || 0))}
+							/>
+						</div>
+					);
+				})}
+			</div>
+			{saveLayout.error && (
+				<p className="text-sm text-amber-600 dark:text-amber-500">
+					{apiErrorMessage(saveLayout.error)}
+				</p>
+			)}
+			<Button size="sm" onClick={onSave} disabled={saveLayout.isPending}>
+				{m.display_arrange_save()}
+			</Button>
+		</div>
+	);
+};
+
+const DisplayRow: FC<{ d: ApiDisplayInfo; busy: boolean; onRelease: () => void }> = ({
+	d,
+	busy,
+	onRelease,
+}) => {
+	const active = d.state === "active";
+	const stateLabel =
+		d.state === "active"
+			? m.display_state_active()
+			: d.state === "pinned"
+				? m.display_state_pinned()
+				: m.display_state_lingering();
+	return (
+		<li className="flex items-center justify-between gap-4 px-4 py-3">
+			<div className="min-w-0">
+				<div className="flex flex-wrap items-center gap-2">
+					<span className="font-medium">{d.mode}</span>
+					<Badge variant={active ? "success" : "secondary"}>{stateLabel}</Badge>
+					{active && d.sessions > 0 && (
+						<Badge variant="outline">{m.display_sessions({ count: d.sessions })}</Badge>
+					)}
+				</div>
+				<code className="text-xs text-muted-foreground">
+					{d.backend}
+					{d.expires_in_ms != null
+						? ` · ${m.display_expires_in({ sec: Math.ceil(d.expires_in_ms / 1000) })}`
+						: ""}
+				</code>
+			</div>
+			{!active && (
+				<Button size="sm" variant="outline" disabled={busy} onClick={onRelease}>
+					{m.display_release_btn()}
+				</Button>
+			)}
+		</li>
+	);
+};
+
+/** The server's `{ error }` message from a thrown `ApiError` (its `.data` body), for inline display. */
+const apiErrorMessage = (err: unknown): string | undefined => {
+	if (err instanceof ApiError) {
+		const data = err.data as { error?: string } | undefined;
+		return data?.error ?? err.message;
+	}
+	return err ? String(err) : undefined;
+};
+
+/** Presets the host can't honor yet (one-click apply would 400) are surfaced but disabled. Empty
+ * now that `gaming-rig` (`keep_alive: forever`) ships: the display is Pinned (Linux + Windows) and
+ * freed via Release. */
+const DISABLED_PRESETS: ReadonlySet<string> = new Set<string>();
+
+const PRESET_LABEL: Record<string, () => string> = {
+	custom: m.display_preset_custom,
+	default: m.display_preset_default,
+	"gaming-rig": m.display_preset_gaming_rig,
+	"shared-desktop": m.display_preset_shared_desktop,
+	hotdesk: m.display_preset_hotdesk,
+	workstation: m.display_preset_workstation,
+};
+
+const TOPOLOGY_LABEL: Record<string, () => string> = {
+	auto: m.display_topology_auto,
+	extend: m.display_topology_extend,
+	primary: m.display_topology_primary,
+	exclusive: m.display_topology_exclusive,
+};
+
+const CONFLICT_LABEL: Record<string, () => string> = {
+	separate: m.display_conflict_separate,
+	steal: m.display_conflict_steal,
+	join: m.display_conflict_join,
+	reject: m.display_conflict_reject,
+};
+
+const IDENTITY_LABEL: Record<string, () => string> = {
+	shared: m.display_identity_shared,
+	"per-client": m.display_identity_per_client,
+	"per-client-mode": m.display_identity_per_client_mode,
+};
+
+const LAYOUT_LABEL: Record<string, () => string> = {
+	"auto-row": m.display_layout_auto_row,
+	manual: m.display_layout_manual,
+};
+
+/** Look up a localized label, tolerating an unknown/undefined key (falls back to the raw value). */
+const tr = (map: Record<string, () => string>, key: string | null | undefined): string => {
+	const fn = key == null ? undefined : map[key];
+	return fn ? fn() : String(key ?? "");
+};
+
+const fmtKeepAlive = (k: KeepAlive): string => {
+	switch (k.mode) {
+		case "off":
+			return m.display_keep_alive_off();
+		case "duration":
+			return `${k.seconds} ${m.display_keep_alive_seconds()}`;
+		case "forever":
+			return "∞";
+	}
+};

web/src/sections/Displays/index.tsx

@@ -0,0 +1,22 @@
+import Section from "@unom/ui/section";
+import type { FC } from "react";
+import { useLocale } from "@/lib/i18n";
+import { m } from "@/paraglide/messages";
+import { DisplaySection } from "./DisplayCard";
+
+/**
+ * The **Virtual displays** page (design/display-management.md): the host's virtual-display policy
+ * (presets + every axis) plus the live-display list + multi-monitor arrangement. Its own nav
+ * section — the config surface is large enough to warrant the room, and it kept the Host page busy.
+ */
+export const SectionDisplays: FC = () => {
+	useLocale();
+	return (
+		<Section maxWidth={false}>
+			<div className="flex flex-col gap-card">
+				<h1 className="text-2xl font-semibold">{m.nav_displays()}</h1>
+				<DisplaySection />
+			</div>
+		</Section>
+	);
+};

web/src/sections/Host/index.tsx

@@ -9,7 +9,5 @@ export const SectionHost: FC = () => {
 	const host = useGetHostInfo();
 	const compositors = useListCompositors();
 
-	return (
+	return <HostView host={host} compositors={compositors} gpu={<GpuSection />} />;
-		<HostView host={host} compositors={compositors} gpu={<GpuSection />} />
-	);
 };