docs(display-management): handoff — mark Stages 0-4 done, Stage 5 started

Update the design doc for handoff: top-of-doc status, a Status/handoff block in §11
(per-stage state, validation boxes, key decisions), and per-stage [DONE]/[STARTED]
markers. Records the decisions that diverged from the plan as written — the Windows
admission default is reject (single-capturer IDD-push), reject is typed (QUIC 0x42),
Stage 5's group-aware exclusive fixes a Stage-3 latent bug — and what's left in
Stage 5 (Mutter/wlroots analogues, layout, /display/layout, per-group restore).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/arch.yml

@@ -0,0 +1,142 @@
+# Build the punktfunk-host / punktfunk-client / punktfunk-web pacman packages from
+# packaging/arch/PKGBUILD and publish them to Gitea's Arch package registry, so Arch boxes
+# get new builds via `pacman -Syu`. Counterpart to deb.yml (apt) and rpm.yml (dnf/rpm-ostree).
+# Arch is rolling, so the packages build against whatever the archlinux:base-devel container
+# resolves today — the same sonames an up-to-date Arch box runs.
+#
+# Registry (public, unom org) — box setup (once), see packaging/arch/README.md. The registry
+# SIGNS the DB + packages, so the box imports the registry key first (pacman-key --add +
+# --lsign-key), then no SigLevel line is needed (pacman's default Required verifies):
+#   [punktfunk]                         # or [punktfunk-canary] for main-push builds
+#   Server = https://git.unom.io/api/packages/unom/arch/$repo/$arch
+#
+# REGISTRY_TOKEN: repo Actions secret, a PAT with write:package scope (shared with docker.yml).
+# NOTE: this token + the registry-held private key are the trust root — a token holder can
+# publish a validly-signed package (the signature attests "via the registry", not "built by CI").
+name: arch
+
+on:
+  push:
+    branches: [main]
+    # Single project version: a `vX.Y.Z` tag is THE release. main publishes to the
+    # `punktfunk-canary` pacman repo as X.Y.Z-0.<run#> (sorts below the eventual X.Y.Z-1),
+    # tags to `punktfunk` — separate repos, so neither channel can shadow the other.
+    tags: ['v*']
+  workflow_dispatch:
+
+env:
+  REGISTRY: git.unom.io
+  OWNER: unom
+
+jobs:
+  build-publish:
+    runs-on: ubuntu-24.04
+    container:
+      image: docker.io/library/archlinux:base-devel
+    timeout-minutes: 90
+    env:
+      CARGO_HOME: /usr/local/cargo
+    steps:
+      # git + nodejs must exist before actions/checkout — base-devel ships neither, and
+      # act_runner runs the action's JS with the CONTAINER's node, it does not inject one.
+      - name: Install build + runtime-dev deps
+        run: |
+          pacman -Syu --noconfirm --needed \
+            git nodejs rust clang cmake nasm pkgconf python \
+            gtk4 libadwaita sdl3 ffmpeg pipewire wayland libxkbcommon opus libei \
+            mesa libglvnd unzip libarchive
+          # bun builds the punktfunk-web console AND is vendored as its runtime (PF_WITH_WEB=1);
+          # it's AUR-only on Arch, so bootstrap the official binary.
+          command -v bun >/dev/null || {
+            curl -fsSL https://bun.sh/install | bash
+            install -m0755 "$HOME/.bun/bin/bun" /usr/local/bin/bun
+          }
+          bun --version
+
+      - uses: actions/checkout@v4
+
+      # Cache cargo's git dir too, not just the registry: the workspace includes
+      # clients/windows, whose windows-reactor/windows deps are git-pinned — cargo must CLONE
+      # them (windows-rs is huge) merely to resolve the workspace, even though nothing Windows
+      # is ever compiled here. Cached, that cost is paid once per runner.
+      - uses: actions/cache@v4
+        with:
+          path: |
+            /usr/local/cargo/registry
+            /usr/local/cargo/git
+          key: cargo-home-arch-${{ hashFiles('Cargo.lock') }}
+          restore-keys: cargo-home-arch-
+
+      - name: Version + channel
+        # vX.Y.Z tag -> X.Y.Z-1 in the `punktfunk` repo; main push -> <next-minor>-0.<run#> in
+        # `punktfunk-canary` (pkgrel accepts only digits+dots — the run number carries the
+        # monotonic ordering; the commit sha is stamped into the binary via the workflow log).
+        run: |
+          eval "$(bash scripts/ci/pf-version.sh)"   # -> PF_BASE (one minor ahead of latest stable)
+          case "$GITHUB_REF" in
+            refs/tags/v*) V="${GITHUB_REF_NAME#v}"; R="1";                       REPO=punktfunk ;;
+            *)            V="$PF_BASE";             R="0.${GITHUB_RUN_NUMBER}";  REPO=punktfunk-canary ;;
+          esac
+          echo "PF_PKGVER=$V" >> "$GITHUB_ENV"
+          echo "PF_PKGREL=$R" >> "$GITHUB_ENV"
+          echo "REPO=$REPO" >> "$GITHUB_ENV"
+          echo "pacman $V-$R -> repo '$REPO'"
+
+      - name: Build packages (makepkg)
+        run: |
+          git config --global --add safe.directory "$PWD"
+          # libcuda link stub — same trick as packaging/rpm/build-rpm.sh: the zerocopy FFI
+          # links -lcuda but the builder has no GPU; synthesize every cu* symbol the source
+          # references so a newly-added call can't silently break the link.
+          CU_SYMS="$(grep -rhoE '\bcu[A-Z][A-Za-z0-9_]*' crates/punktfunk-host/src/ | sort -u || true)"
+          if [ -n "$CU_SYMS" ] && [ ! -e /usr/lib/libcuda.so ]; then
+            STUB_C="$(mktemp --suffix=.c)"
+            for s in $CU_SYMS; do printf 'int %s(void){return 0;}\n' "$s" >> "$STUB_C"; done
+            gcc -shared -fPIC -Wl,-soname,libcuda.so.1 -o /usr/lib/libcuda.so.1 "$STUB_C"
+            ln -sf libcuda.so.1 /usr/lib/libcuda.so
+            rm -f "$STUB_C"; ldconfig
+            echo "== libcuda stub: $(printf '%s\n' "$CU_SYMS" | wc -l) symbols =="
+          fi
+          # makepkg refuses to run as root; deps are already installed above (-d skips the
+          # RPM-level check that can't see the script-installed bun anyway).
+          useradd -m builder
+          mkdir -p "$CARGO_HOME"   # actions/cache doesn't create it on a cache miss
+          chown -R builder: "$PWD" "$CARGO_HOME"
+          sudo -u builder git config --global --add safe.directory "$PWD"
+          mkdir -p dist && chown builder: dist
+          cd packaging/arch
+          sudo -u builder env PF_SRCDIR="$GITHUB_WORKSPACE" PF_WITH_WEB=1 \
+            PF_PKGVER="$PF_PKGVER" PF_PKGREL="$PF_PKGREL" \
+            CARGO_HOME="$CARGO_HOME" PKGDEST="$GITHUB_WORKSPACE/dist" \
+            makepkg -f -d --holdver
+          ls -lh "$GITHUB_WORKSPACE/dist"
+
+      - name: Publish to the Gitea Arch registry
+        env:
+          TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+        run: |
+          for pkg in dist/*.pkg.tar.zst; do
+            echo "uploading $pkg"
+            NAME=$(bsdtar -xOf "$pkg" .PKGINFO | sed -n 's/^pkgname = //p')
+            VER=$(bsdtar -xOf "$pkg" .PKGINFO | sed -n 's/^pkgver = //p')
+            ARCH=$(bsdtar -xOf "$pkg" .PKGINFO | sed -n 's/^arch = //p')
+            # A re-tagged release re-fires this workflow and the registry 409s on duplicate
+            # package versions — delete any prior copy first (404 on the first publish is fine).
+            curl -fsS -o /dev/null --user "enricobuehler:$TOKEN" -X DELETE \
+              "https://$REGISTRY/api/packages/$OWNER/arch/$REPO/$NAME/$VER/$ARCH" || true
+            curl -fsS --user "enricobuehler:$TOKEN" --upload-file "$pkg" \
+              "https://$REGISTRY/api/packages/$OWNER/arch/$REPO"
+          done
+          echo "published to $OWNER/arch/$REPO"
+
+      # On a real release, also attach the packages to the unified Gitea Release.
+      - name: Attach packages to the Gitea release (stable tags only)
+        if: startsWith(gitea.ref, 'refs/tags/v')
+        env:
+          GITEA_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+        run: |
+          . scripts/ci/gitea-release.sh
+          RID=$(ensure_release "$GITHUB_REF_NAME" "$GITHUB_REF_NAME" auto)
+          for pkg in dist/*.pkg.tar.zst; do
+            upsert_asset "$RID" "$pkg"
+          done

.gitea/workflows/rpm.yml

@@ -35,8 +35,10 @@ jobs:
         include:
           - image: punktfunk-fedora-rpm     # Fedora 43 == Bazzite base
             group: bazzite
+            fedver: 43
           - image: punktfunk-fedora44-rpm   # Fedora 44 == Fedora KDE spin
             group: fedora-44
+            fedver: 44
     container:
       image: git.unom.io/unom/${{ matrix.image }}:latest
     timeout-minutes: 90
@@ -53,6 +55,8 @@ jobs:
         run: |
           git config --global --add safe.directory "$PWD"
           dnf -y install gtk4-devel libadwaita-devel SDL3-devel
+          # sysext build (packaging/bazzite/build-sysext.sh): squashfs + SELinux labeling.
+          dnf -y install squashfs-tools cpio libselinux-utils selinux-policy-targeted
           # bun builds the punktfunk-web console (--with web). Baked into the image; install it
           # here too so the job stays green against the PREVIOUS image (docker.yml bootstrap note).
           command -v bun >/dev/null || {
@@ -117,6 +121,27 @@ jobs:
           done
           echo "published to $OWNER/rpm/$GROUP"
 
+      # The no-layering Bazzite path: wrap the just-built host + web RPMs into a systemd-sysext
+      # image and publish it to the per-Fedora-major feed (punktfunk-sysext/f43[-canary], …) that
+      # `punktfunk-sysext install|update` reads. Same RPMs, same channels — just no rpm-ostree.
+      - name: Build the sysext image
+        run: |
+          bash packaging/bazzite/build-sysext.sh --version-id "${{ matrix.fedver }}" \
+            --out "dist-sysext/punktfunk-${PF_VERSION}-${PF_RELEASE}-x86-64.raw" \
+            dist/punktfunk-"${PF_VERSION}-${PF_RELEASE}"*.rpm \
+            dist/punktfunk-web-"${PF_VERSION}-${PF_RELEASE}"*.rpm
+
+      - name: Publish the sysext feed
+        env:
+          TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+        run: |
+          case "$GROUP" in
+            *-canary) FEED="f${{ matrix.fedver }}-canary"; KEEP=6 ;;  # rolling: bound the pile-up
+            *)        FEED="f${{ matrix.fedver }}";        KEEP=0 ;;  # stable: keep every release
+          esac
+          KEEP=$KEEP bash packaging/bazzite/publish-sysext-feed.sh "$FEED" \
+            "dist-sysext/punktfunk-${PF_VERSION}-${PF_RELEASE}-x86-64.raw"
+
       # On a real release, also attach the .rpms to the unified Gitea Release. Both Fedora bases
       # (bazzite=F43, fedora-44) build the SAME filename, so suffix the asset with the base to keep
       # both on the release; canary builds live in the `*-canary` rpm groups (no release page).
@@ -132,3 +157,6 @@ jobs:
             base="$(basename "$rpm" .rpm)"
             upsert_asset "$RID" "$rpm" "${base}.${{ matrix.group }}.rpm"
           done
+          for raw in dist-sysext/*.raw; do
+            upsert_asset "$RID" "$raw" "$(basename "$raw" .raw).f${{ matrix.fedver }}.raw"
+          done

Cargo.lock

@@ -2129,7 +2129,7 @@ dependencies = [
 
 [[package]]
 name = "latency-probe"
-version = "0.7.2"
+version = "0.7.4"
 
 [[package]]
 name = "lazy_static"
@@ -2261,7 +2261,7 @@ checksum = "0ceec5bc11778974d1bcb055b18002eba7f4b3518b6a0081b3af5f21666da9ad"
 
 [[package]]
 name = "loss-harness"
-version = "0.7.2"
+version = "0.7.4"
 dependencies = [
  "punktfunk-core",
 ]
@@ -2908,7 +2908,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-client-android"
-version = "0.7.2"
+version = "0.7.4"
 dependencies = [
  "android_logger",
  "jni",
@@ -2922,7 +2922,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-client-linux"
-version = "0.7.2"
+version = "0.7.4"
 dependencies = [
  "anyhow",
  "async-channel",
@@ -2945,7 +2945,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-client-windows"
-version = "0.7.2"
+version = "0.7.4"
 dependencies = [
  "anyhow",
  "async-channel",
@@ -2968,7 +2968,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-core"
-version = "0.7.2"
+version = "0.7.4"
 dependencies = [
  "aes-gcm",
  "bytes",
@@ -2999,7 +2999,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-host"
-version = "0.7.2"
+version = "0.7.4"
 dependencies = [
  "aes",
  "aes-gcm",
@@ -3071,7 +3071,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-probe"
-version = "0.7.2"
+version = "0.7.4"
 dependencies = [
  "anyhow",
  "mdns-sd",
@@ -3085,7 +3085,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-tray"
-version = "0.7.2"
+version = "0.7.4"
 dependencies = [
  "anyhow",
  "ksni",

Cargo.toml

@@ -17,7 +17,7 @@ members = [
 exclude = ["packaging/linux/steam-deck-gadget/usbip-poc"]
 
 [workspace.package]
-version = "0.7.2"
+version = "0.7.4"
 edition = "2021"
 rust-version = "1.82"
 license = "MIT OR Apache-2.0"

README.md

@@ -83,8 +83,9 @@ Windows host also ships as a signed installer (all-vendor: NVIDIA, AMD, Intel).
 | Platform | Install | Guide |
 |--------|---------|-------|
 | **Ubuntu / Debian** (apt) | `sudo apt install punktfunk-host` *(after adding the repo)* | [Ubuntu — GNOME](https://docs.punktfunk.unom.io/docs/ubuntu-gnome) · [KDE](https://docs.punktfunk.unom.io/docs/ubuntu-kde) |
-| **Fedora / Bazzite** (rpm-ostree) | `rpm-ostree install punktfunk punktfunk-web` *(or the bootc image)* | [Fedora — KDE](https://docs.punktfunk.unom.io/docs/fedora-kde) · [Bazzite](https://docs.punktfunk.unom.io/docs/bazzite) |
-| **Arch / Steam Deck** (PKGBUILD / sysext) | `makepkg -si` *(Arch)* · sysext `.raw` *(SteamOS)* | [packaging/arch](packaging/arch/README.md) |
+| **Bazzite / Fedora Atomic** (systemd-sysext) | `sudo bash punktfunk-sysext.sh install` *(no layering, no reboot; rpm-ostree + bootc also supported)* | [Bazzite](https://docs.punktfunk.unom.io/docs/bazzite) |
+| **Fedora** (dnf) | `dnf install punktfunk punktfunk-web` *(after adding the repo)* | [Fedora — KDE](https://docs.punktfunk.unom.io/docs/fedora-kde) |
+| **Arch / Steam Deck** (pacman / sysext) | `pacman -Sy punktfunk-host` *(binary repo)* · sysext `.raw` *(SteamOS)* | [packaging/arch](packaging/arch/README.md) |
 | **Windows** (11 22H2+, x64) | signed `setup.exe` from the package registry | [Windows Host](https://docs.punktfunk.unom.io/docs/windows-host) |
 
 `punktfunk-host` is the streaming host; `punktfunk-web` is the browser console (pairing + status).

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 +138,172 @@
         }
       }
     },
+    "/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": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          }
+        }
+      },
+      "put": {
+        "tags": [
+          "display"
+        ],
+        "summary": "Set the display-management policy",
+        "description": "Persists a new policy (validated + clamped) and applies it from the next connect/teardown — a\nrunning session keeps the display it opened on. `keep_alive: forever` is rejected until the\ndisplay-lifecycle stage ships (it would keep physical monitors dark indefinitely with no release\npath yet).",
+        "operationId": "setDisplaySettings",
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/DisplayPolicy"
+              }
+            }
+          },
+          "required": true
+        },
+        "responses": {
+          "200": {
+            "description": "Policy stored; the new state",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/DisplaySettingsState"
+                }
+              }
+            }
+          },
+          "400": {
+            "description": "An option value is not yet supported (e.g. keep_alive forever)",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$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 +1767,59 @@
           "av1"
         ]
       },
+      "ApiDisplayInfo": {
+        "type": "object",
+        "description": "One live or kept virtual display.",
+        "required": [
+          "slot",
+          "backend",
+          "mode",
+          "state",
+          "sessions"
+        ],
+        "properties": {
+          "backend": {
+            "type": "string",
+            "description": "Backend name (`pf-vdisplay`, `kwin`, …)."
+          },
+          "client": {
+            "type": [
+              "string",
+              "null"
+            ],
+            "description": "Short client label, when the owner tracks it."
+          },
+          "expires_in_ms": {
+            "type": [
+              "integer",
+              "null"
+            ],
+            "format": "int64",
+            "description": "Milliseconds until a lingering display is torn down (absent when active/pinned).",
+            "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`."
+          }
+        }
+      },
       "ApiError": {
         "type": "object",
         "description": "Error envelope for every non-2xx response.",
@@ -1909,6 +2128,130 @@
           }
         }
       },
+      "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": {
+            "$ref": "#/components/schemas/EffectivePolicy",
+            "description": "The effective (preset-expanded) policy currently in force."
+          },
+          "enforced": {
+            "type": "array",
+            "items": {
+              "type": "string"
+            },
+            "description": "Option names this build enforces right now (e.g. `keep_alive`, `topology`). The remaining\nstored options (`mode_conflict`, `identity`, `layout`) land in later stages — surfaced so the\nconsole can mark them \"coming soon\" instead of implying they already take effect."
+          },
+          "presets": {
+            "type": "array",
+            "items": {
+              "$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 +2442,72 @@
           }
         }
       },
+      "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 +2527,32 @@
           }
         }
       },
+      "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.",
@@ -2242,6 +2677,16 @@
           }
         }
       },
+      "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 +2884,88 @@
           }
         }
       },
+      "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 +3267,16 @@
             "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 +3300,10 @@
       "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/decky/src/index.tsx

@@ -80,7 +80,7 @@ const QamPanel: FC = () => {
       {/* Pinned games — the "jump straight into Playnite" rows. Pin games from a host's
           picker (fullscreen page → host row → games button). */}
       {pins.pins.length > 0 && (
-        <PanelSection title="Games">
+        <PanelSection title="Pinned Games">
           {pins.pins.map((pin) => {
             const { online } = resolvePinHost(pin, hosts);
             return (

clients/decky/src/library.tsx

@@ -3,13 +3,14 @@
 // can take seconds, hence the explicit spinner copy) and pins titles as one-tap rows in
 // the QAM's Games section; its header also launches the GTK client's on-screen gamepad
 // library (`--browse`).
-import { DialogButton, Field, Focusable, ModalRoot, Spinner, showModal } from "@decky/ui";
-import { CSSProperties, FC, useEffect, useState } from "react";
+import { DialogButton, Field, ModalRoot, Spinner, showModal } from "@decky/ui";
+import { FC, useEffect, useState } from "react";
 import { FaThLarge, FaTv } from "react-icons/fa";
 import { GameEntry, Host, library, LibraryResult, PinnedGame } from "./backend";
 import { PinsApi, resolvePinHost, startBrowse, startStream } from "./hooks";
 import { isSafeLaunchId } from "./steam";
 import { PairModal } from "./pair";
+import { RowActions, actionButton } from "./ui";
 
 /** Human store tag (mirrors the GTK client's `store_label`). */
 export function storeLabel(store: string): string {
@@ -58,12 +59,6 @@ export function streamPin(pin: PinnedGame, live: Host[], pins: PinsApi): void {
   void startStream(host, { launchId: pin.game_id }, pin.title);
 }
 
-const pickButton: CSSProperties = {
-  width: "fit-content",
-  minWidth: "5em",
-  flexShrink: 0,
-};
-
 // Copy per backend error code (LibraryResult.error); `detail` covers the generic case.
 function errorCopy(res: LibraryResult): string {
   switch (res.error) {
@@ -143,16 +138,18 @@ export const GamePickerModal: FC<{
         description="Browse this host's games with the controller, full screen"
         childrenContainerWidth="max"
       >
-        <DialogButton
-          style={pickButton}
-          onClick={() => {
-            closeModal?.();
-            void startBrowse(host);
-          }}
-        >
-          <FaTv style={{ marginRight: "0.4em" }} />
-          Open
-        </DialogButton>
+        <RowActions>
+          <DialogButton
+            style={actionButton}
+            onClick={() => {
+              closeModal?.();
+              void startBrowse(host);
+            }}
+          >
+            <FaTv style={{ marginRight: "0.4em" }} />
+            Open
+          </DialogButton>
+        </RowActions>
       </Field>
 
       {clientUpdatePending && (
@@ -177,10 +174,10 @@ export const GamePickerModal: FC<{
 
       {result !== null && !result.ok && (
         <Field label="Couldn't fetch the library" description={errorCopy(result)} childrenContainerWidth="max">
-          <Focusable style={{ display: "flex", gap: "0.5em", justifyContent: "flex-end" }}>
+          <RowActions>
             {result.error === "not-paired" && (
               <DialogButton
-                style={pickButton}
+                style={actionButton}
                 onClick={() =>
                   showModal(<PairModal host={host} onPaired={() => setAttempt((n) => n + 1)} />)
                 }
@@ -188,10 +185,10 @@ export const GamePickerModal: FC<{
                 Pair
               </DialogButton>
             )}
-            <DialogButton style={pickButton} onClick={() => setAttempt((n) => n + 1)}>
+            <DialogButton style={actionButton} onClick={() => setAttempt((n) => n + 1)}>
               Retry
             </DialogButton>
-          </Focusable>
+          </RowActions>
         </Field>
       )}
 
@@ -217,10 +214,12 @@ export const GamePickerModal: FC<{
                 }
                 childrenContainerWidth="max"
               >
-                <DialogButton style={pickButton} disabled={!safe} onClick={() => togglePin(g)}>
-                  <FaThLarge style={{ marginRight: "0.4em" }} />
-                  {pinned ? "Unpin" : "Pin"}
-                </DialogButton>
+                <RowActions>
+                  <DialogButton style={actionButton} disabled={!safe} onClick={() => togglePin(g)}>
+                    <FaThLarge style={{ marginRight: "0.4em" }} />
+                    {pinned ? "Unpin" : "Pin"}
+                  </DialogButton>
+                </RowActions>
               </Field>
             );
           })}

clients/decky/src/page.tsx

@@ -10,6 +10,7 @@ import {
   showModal,
   staticClasses,
 } from "@decky/ui";
+import { RowActions, actionButton, iconButton } from "./ui";
 import { toaster } from "@decky/api";
 import { CSSProperties, FC, useState } from "react";
 import {
@@ -58,27 +59,6 @@ const tabScroll: CSSProperties = {
   boxSizing: "border-box",
 };
 
-// DialogButton stretches to 100% width in the gamepad UI — on a fullscreen row that means a
-// screen-wide button. Size action buttons to their content instead (right-aligned by the
-// Field's children container).
-const actionButton: CSSProperties = {
-  width: "fit-content",
-  minWidth: "6em",
-  flexShrink: 0,
-};
-// Square icon-only button (details ⓘ, header back arrow) — needs an explicit height too, or
-// the zero padding collapses it to the icon's line height.
-const iconButton: CSSProperties = {
-  width: "40px",
-  minWidth: "40px",
-  height: "40px",
-  padding: 0,
-  flexShrink: 0,
-  display: "flex",
-  alignItems: "center",
-  justifyContent: "center",
-};
-
 // ----------------------------------------------------------------------------------------
 // Host details — everything the mDNS advert told us, incl. the fingerprint to cross-check
 // against the host's own log / web console before trusting it.
@@ -144,7 +124,7 @@ const HostRow: FC<{ host: Host; onPaired: () => void; onGames: () => void }> = (
       }`}
       childrenContainerWidth="max"
     >
-      <Focusable style={{ display: "flex", gap: "0.5em", justifyContent: "flex-end" }}>
+      <RowActions>
         <DialogButton
           style={iconButton}
           onClick={() => showModal(<HostDetailsModal host={host} />)}
@@ -153,13 +133,13 @@ const HostRow: FC<{ host: Host; onPaired: () => void; onGames: () => void }> = (
         </DialogButton>
         {/* Labeled, not icon-only: this is the entry to the game picker AND the on-screen
             library browser, and controller nav has no hover tooltip to explain a bare icon. */}
-        <DialogButton style={{ ...actionButton, minWidth: "6em" }} onClick={onGames}>
+        <DialogButton style={actionButton} onClick={onGames}>
           <FaThLarge style={{ marginRight: "0.4em" }} />
           Games
         </DialogButton>
         {needsPair && (
           <DialogButton
-            style={{ ...actionButton, minWidth: "5em" }}
+            style={actionButton}
             onClick={() => showModal(<PairModal host={host} onPaired={onPaired} />)}
           >
             Pair
@@ -178,7 +158,7 @@ const HostRow: FC<{ host: Host; onPaired: () => void; onGames: () => void }> = (
           <FaPlay style={{ marginRight: "0.4em" }} />
           Stream
         </DialogButton>
-      </Focusable>
+      </RowActions>
     </Field>
   );
 };
@@ -201,14 +181,16 @@ const HostsTab: FC<{
       childrenContainerWidth="max"
       bottomSeparator={hosts.length ? "standard" : "none"}
     >
-      <DialogButton style={{ ...actionButton, minWidth: "8em" }} disabled={scanning} onClick={refresh}>
-        {scanning ? (
-          <Spinner style={{ height: "1em", marginRight: "0.5em" }} />
-        ) : (
-          <FaSyncAlt style={{ marginRight: "0.5em" }} />
-        )}
-        {scanning ? "Scanning…" : "Refresh"}
-      </DialogButton>
+      <RowActions>
+        <DialogButton style={actionButton} disabled={scanning} onClick={refresh}>
+          {scanning ? (
+            <Spinner style={{ height: "1em", marginRight: "0.5em" }} />
+          ) : (
+            <FaSyncAlt style={{ marginRight: "0.5em" }} />
+          )}
+          {scanning ? "Scanning…" : "Refresh"}
+        </DialogButton>
+      </RowActions>
     </Field>
 
     {hosts.length === 0 && !scanning && (
@@ -251,18 +233,18 @@ const HostsTab: FC<{
               }${pin.paired ? "" : " · pairing required"}`}
               childrenContainerWidth="max"
             >
-              <Focusable style={{ display: "flex", gap: "0.5em", justifyContent: "flex-end" }}>
+              <RowActions>
                 <DialogButton style={actionButton} onClick={() => streamPin(pin, hosts, pins)}>
                   <FaPlay style={{ marginRight: "0.4em" }} />
                   Play
                 </DialogButton>
                 <DialogButton
-                  style={{ ...actionButton, minWidth: "5em" }}
+                  style={actionButton}
                   onClick={() => pins.removePin(pin.host_fp, pin.game_id)}
                 >
                   Remove
                 </DialogButton>
-              </Focusable>
+              </RowActions>
             </Field>
           );
         })}
@@ -306,13 +288,15 @@ const AboutTab: FC<{
       }
       childrenContainerWidth="max"
     >
-      <DialogButton
-        style={{ ...actionButton, minWidth: "11em" }}
-        disabled={checking}
-        onClick={() => void checkForUpdatesNow(check)}
-      >
-        {checking ? <Spinner style={{ height: "1em" }} /> : "Check for updates"}
-      </DialogButton>
+      <RowActions>
+        <DialogButton
+          style={actionButton}
+          disabled={checking}
+          onClick={() => void checkForUpdatesNow(check)}
+        >
+          {checking ? <Spinner style={{ height: "1em" }} /> : "Check for updates"}
+        </DialogButton>
+      </RowActions>
     </Field>
     {hasUpdate(update) && (
       <Field
@@ -326,13 +310,12 @@ const AboutTab: FC<{
         description="Installing can take a couple of minutes; Decky reloads the plugin when done"
         childrenContainerWidth="max"
       >
-        <DialogButton
-          style={{ ...actionButton, minWidth: "9em" }}
-          onClick={() => applyUpdate(update!, check)}
-        >
-          <FaDownload style={{ marginRight: "0.4em" }} />
-          Update
-        </DialogButton>
+        <RowActions>
+          <DialogButton style={actionButton} onClick={() => applyUpdate(update!, check)}>
+            <FaDownload style={{ marginRight: "0.4em" }} />
+            Update
+          </DialogButton>
+        </RowActions>
       </Field>
     )}
     <Field
@@ -340,13 +323,15 @@ const AboutTab: FC<{
       description="Hosts, pairing, controllers, and troubleshooting — docs.punktfunk.unom.io"
       childrenContainerWidth="max"
     >
-      <DialogButton
-        style={{ ...actionButton, minWidth: "8em" }}
-        onClick={() => Navigation.NavigateToExternalWeb(DOCS_URL)}
-      >
-        <FaExternalLinkAlt style={{ marginRight: "0.4em" }} />
-        Open
-      </DialogButton>
+      <RowActions>
+        <DialogButton
+          style={actionButton}
+          onClick={() => Navigation.NavigateToExternalWeb(DOCS_URL)}
+        >
+          <FaExternalLinkAlt style={{ marginRight: "0.4em" }} />
+          Open
+        </DialogButton>
+      </RowActions>
     </Field>
     <Field
       focusable={false}
@@ -358,9 +343,11 @@ const AboutTab: FC<{
       description="Force-stop the stream client if a session wedges"
       childrenContainerWidth="max"
     >
-      <DialogButton style={{ ...actionButton, minWidth: "8em" }} onClick={() => void forceStopStream()}>
-        Force-stop
-      </DialogButton>
+      <RowActions>
+        <DialogButton style={actionButton} onClick={() => void forceStopStream()}>
+          Force-stop
+        </DialogButton>
+      </RowActions>
     </Field>
   </div>
 );
@@ -399,16 +386,21 @@ const PunktfunkPage: FC = () => {
         </div>
       </Focusable>
 
-      {/* overflow:hidden is load-bearing: Valve's Tabs slides the incoming panel in from the
-          right on L1/R1, and with autoFocusContents it scrollIntoViews a control inside that
-          still-offscreen panel. Without a clip here the scroll pans #GamepadUI itself — the whole
-          Steam UI (top bar included) slides left until you click a tab. Valve's own Tabs always
-          live in a clipped flex box; match that. */}
+      {/* Two things fight each other on an L1/R1 tab switch:
+          1. Valve's Tabs slides the incoming panel in from the right with a CSS transform.
+          2. `autoFocusContents` then focuses a control inside that still-offscreen panel, which
+             fires scrollIntoView. Because the panel is offset by a *transform* (not by scroll
+             position), scrollIntoView can't satisfy it by scrolling any one ancestor, so it walks
+             up and pans the whole page — the "screen jumps right, then animates back" glitch.
+          Dropping autoFocusContents removes the scrollIntoView entirely, so nothing fights the
+          slide. L1/R1 still cycles tabs (that handler lives on the Tabs focus scope, active while
+          focus is anywhere inside — including the tab strip); after a switch, focus stays on the
+          strip and Down enters the content, which is how Steam's own tabbed pages behave.
+          The overflow:hidden clip stays as defense-in-depth against any stray horizontal pan. */}
       <div style={{ flex: 1, minHeight: 0, overflow: "hidden" }}>
         <Tabs
           activeTab={tab}
           onShowTab={(id: string) => setTab(id)}
-          autoFocusContents
           tabs={[
             {
               id: "hosts",

clients/decky/src/settings.tsx

@@ -2,8 +2,20 @@
 // the flatpak client's JSON (main.py set_settings), which the client reads on launch. The
 // accepted gamepad/compositor names mirror punktfunk-core's `*Pref::from_name`.
 import { Dropdown, Field, SliderField, Spinner, ToggleField } from "@decky/ui";
-import { FC, useEffect, useState } from "react";
+import { CSSProperties, FC, useEffect, useState } from "react";
 import { getSettings, setSettings, StreamSettings } from "./backend";
+import { RowActions } from "./ui";
+
+// Decky's Dropdown has no width prop — it fills whatever container it's in, and a
+// `childrenContainerWidth="max"` Field is the whole row. Wrapping it in this fit-content shell
+// (inside the right-aligned RowActions) shrinks the control to its selected label, with a floor
+// so short values like "60 Hz" don't collapse to a nub and a ceiling so nothing runs edge to
+// edge. Matches the right-aligned, content-sized buttons everywhere else.
+const selectShell: CSSProperties = {
+  width: "fit-content",
+  minWidth: "10em",
+  maxWidth: "24em",
+};
 
 const RESOLUTIONS: [number, number, string][] = [
   [0, 0, "Native display"],
@@ -61,21 +73,29 @@ export const SettingsSection: FC = () => {
         description="The host creates a virtual output at exactly this size"
         childrenContainerWidth="max"
       >
-        <Dropdown
-          rgOptions={RESOLUTIONS.map(([, , label], i) => ({ data: i, label }))}
-          selectedOption={resIdx}
-          onChange={(o) => {
-            const [w, h] = RESOLUTIONS[o.data as number];
-            patch({ width: w, height: h });
-          }}
-        />
+        <RowActions>
+          <div style={selectShell}>
+            <Dropdown
+              rgOptions={RESOLUTIONS.map(([, , label], i) => ({ data: i, label }))}
+              selectedOption={resIdx}
+              onChange={(o) => {
+                const [w, h] = RESOLUTIONS[o.data as number];
+                patch({ width: w, height: h });
+              }}
+            />
+          </div>
+        </RowActions>
       </Field>
       <Field label="Refresh rate" childrenContainerWidth="max">
-        <Dropdown
-          rgOptions={REFRESH.map((r) => ({ data: r, label: r === 0 ? "Native" : `${r} Hz` }))}
-          selectedOption={s.refresh_hz}
-          onChange={(o) => patch({ refresh_hz: o.data as number })}
-        />
+        <RowActions>
+          <div style={selectShell}>
+            <Dropdown
+              rgOptions={REFRESH.map((r) => ({ data: r, label: r === 0 ? "Native" : `${r} Hz` }))}
+              selectedOption={s.refresh_hz}
+              onChange={(o) => patch({ refresh_hz: o.data as number })}
+            />
+          </div>
+        </RowActions>
       </Field>
       <SliderField
         label="Bitrate"
@@ -93,11 +113,15 @@ export const SettingsSection: FC = () => {
         description="Which virtual controller the host creates for your inputs"
         childrenContainerWidth="max"
       >
-        <Dropdown
-          rgOptions={GAMEPADS.map((g) => ({ data: g, label: GAMEPAD_LABELS[g] ?? g }))}
-          selectedOption={s.gamepad}
-          onChange={(o) => patch({ gamepad: o.data as string })}
-        />
+        <RowActions>
+          <div style={selectShell}>
+            <Dropdown
+              rgOptions={GAMEPADS.map((g) => ({ data: g, label: GAMEPAD_LABELS[g] ?? g }))}
+              selectedOption={s.gamepad}
+              onChange={(o) => patch({ gamepad: o.data as string })}
+            />
+          </div>
+        </RowActions>
       </Field>
       {(s.gamepad === "steamdeck" || s.gamepad === "auto") && (
         <Field
@@ -110,11 +134,15 @@ export const SettingsSection: FC = () => {
         description="Which compositor backend the host uses for the virtual display — Automatic suits almost every host"
         childrenContainerWidth="max"
       >
-        <Dropdown
-          rgOptions={COMPOSITORS.map((c) => ({ data: c, label: COMPOSITOR_LABELS[c] ?? c }))}
-          selectedOption={s.compositor}
-          onChange={(o) => patch({ compositor: o.data as string })}
-        />
+        <RowActions>
+          <div style={selectShell}>
+            <Dropdown
+              rgOptions={COMPOSITORS.map((c) => ({ data: c, label: COMPOSITOR_LABELS[c] ?? c }))}
+              selectedOption={s.compositor}
+              onChange={(o) => patch({ compositor: o.data as string })}
+            />
+          </div>
+        </RowActions>
       </Field>
       <ToggleField
         label="Stream microphone"

clients/decky/src/ui.tsx

@@ -0,0 +1,46 @@
+// Shared UI primitives for the fullscreen page + modals. The one rule that keeps every row
+// looking consistent: a Field's action(s) always sit right-aligned, with real space between
+// them and the label text — never hugging it.
+//
+// Decky lays a Field out as `[ label .......... children ]`. When the children container is
+// grown (`childrenContainerWidth="max"`, which we want so multi-button clusters have room), a
+// bare `fit-content` button LEFT-aligns inside that grown container and ends up pressed against
+// the label with the space wasted to its right. Wrapping the action(s) in `RowActions` pushes
+// them to the right edge and evenly spaces multiples — the same treatment every row now gets.
+import { Focusable } from "@decky/ui";
+import { CSSProperties, FC, ReactNode } from "react";
+
+export const RowActions: FC<{ children: ReactNode }> = ({ children }) => (
+  <Focusable
+    style={{
+      display: "flex",
+      gap: "0.5em",
+      justifyContent: "flex-end",
+      alignItems: "center",
+    }}
+  >
+    {children}
+  </Focusable>
+);
+
+// A single action button sized to its content (not the gamepad-UI default of 100% width), with
+// a floor so short labels ("Pair", "Remove") don't render as tiny nubs and every row's button
+// reads at the same weight.
+export const actionButton: CSSProperties = {
+  width: "fit-content",
+  minWidth: "7em",
+  flexShrink: 0,
+};
+
+// Square icon-only button (details ⓘ, header back arrow). Needs an explicit height or the zero
+// padding collapses it to the icon's line height.
+export const iconButton: CSSProperties = {
+  width: "40px",
+  minWidth: "40px",
+  height: "40px",
+  padding: 0,
+  flexShrink: 0,
+  display: "flex",
+  alignItems: "center",
+  justifyContent: "center",
+};

clients/linux/src/video_gl.rs

@@ -30,15 +30,17 @@ use std::sync::{Arc, Mutex};
 
 // --- EGL_EXT_image_dma_buf_import(+_modifiers) constants (khronos-egl exposes none) ------
 const EGL_LINUX_DMA_BUF_EXT: egl::Enum = 0x3270;
-const EGL_LINUX_DRM_FOURCC_EXT: usize = 0x3271;
-const EGL_DMA_BUF_PLANE0_FD_EXT: usize = 0x3272;
-const EGL_DMA_BUF_PLANE0_OFFSET_EXT: usize = 0x3273;
-const EGL_DMA_BUF_PLANE0_PITCH_EXT: usize = 0x3274;
-const EGL_DMA_BUF_PLANE0_MODIFIER_LO_EXT: usize = 0x3443;
-const EGL_DMA_BUF_PLANE0_MODIFIER_HI_EXT: usize = 0x3444;
-const EGL_WIDTH: usize = 0x3057;
-const EGL_HEIGHT: usize = 0x3056;
-const EGL_NONE: usize = 0x3038;
+// eglCreateImageKHR takes 32-bit EGLint attribs (the core-1.5 eglCreateImage variant is the
+// one with pointer-sized EGLAttrib) — using the wrong width feeds the driver garbage pairs.
+const EGL_LINUX_DRM_FOURCC_EXT: i32 = 0x3271;
+const EGL_DMA_BUF_PLANE0_FD_EXT: i32 = 0x3272;
+const EGL_DMA_BUF_PLANE0_OFFSET_EXT: i32 = 0x3273;
+const EGL_DMA_BUF_PLANE0_PITCH_EXT: i32 = 0x3274;
+const EGL_DMA_BUF_PLANE0_MODIFIER_LO_EXT: i32 = 0x3443;
+const EGL_DMA_BUF_PLANE0_MODIFIER_HI_EXT: i32 = 0x3444;
+const EGL_WIDTH: i32 = 0x3057;
+const EGL_HEIGHT: i32 = 0x3056;
+const EGL_NONE: i32 = 0x3038;
 const DRM_FORMAT_MOD_INVALID: u64 = 0x00ff_ffff_ffff_ffff;
 
 /// `fourcc('N','V','1','2')` — the only decoder output today (8-bit 4:2:0). P010 joins when
@@ -140,7 +142,7 @@ type EglCreateImageKhr = unsafe extern "C" fn(
     *mut c_void, // EGLContext (EGL_NO_CONTEXT for dmabuf)
     egl::Enum,
     *mut c_void, // EGLClientBuffer (null for dmabuf)
-    *const usize,
+    *const i32,  // EGLint attrib list (KHR variant — NOT pointer-sized EGLAttrib)
 ) -> *const c_void;
 type EglDestroyImageKhr = unsafe extern "C" fn(*mut c_void, *const c_void) -> egl::Boolean;
 
@@ -464,24 +466,24 @@ impl GlConverter {
     ) -> Result<*const c_void> {
         let mut attribs = vec![
             EGL_WIDTH,
-            width as usize,
+            width as i32,
             EGL_HEIGHT,
-            height as usize,
+            height as i32,
             EGL_LINUX_DRM_FOURCC_EXT,
-            fourcc as usize,
+            fourcc as i32,
             EGL_DMA_BUF_PLANE0_FD_EXT,
-            plane.fd as usize,
+            plane.fd,
             EGL_DMA_BUF_PLANE0_OFFSET_EXT,
-            plane.offset as usize,
+            plane.offset as i32,
             EGL_DMA_BUF_PLANE0_PITCH_EXT,
-            plane.stride as usize,
+            plane.stride as i32,
         ];
         if modifier != DRM_FORMAT_MOD_INVALID && modifier != 0 {
             attribs.extend_from_slice(&[
                 EGL_DMA_BUF_PLANE0_MODIFIER_LO_EXT,
-                (modifier & 0xffff_ffff) as usize,
+                (modifier & 0xffff_ffff) as u32 as i32,
                 EGL_DMA_BUF_PLANE0_MODIFIER_HI_EXT,
-                (modifier >> 32) as usize,
+                (modifier >> 32) as u32 as i32,
             ]);
         }
         attribs.push(EGL_NONE);
@@ -497,12 +499,12 @@ impl GlConverter {
         };
         if img.is_null() {
             bail!(
-                "eglCreateImageKHR rejected plane ({}x{} {:#x} mod {:#018x}): {:#x}",
+                "eglCreateImageKHR rejected plane ({}x{} {:#x} mod {:#018x}): {:?}",
                 width,
                 height,
                 fourcc,
                 modifier,
-                self.egl.get_error().map(|e| e as u32).unwrap_or(0)
+                self.egl.get_error()
             );
         }
         Ok(img)

clients/probe/src/main.rs

@@ -412,7 +412,7 @@ async fn session(args: Args) -> Result<()> {
     io::write_msg(
         &mut send,
         &Hello {
-            abi_version: punktfunk_core::ABI_VERSION,
+            abi_version: punktfunk_core::WIRE_VERSION,
             mode: args.mode,
             compositor: args.compositor,
             gamepad: args.gamepad,

crates/punktfunk-core/src/client.rs

@@ -876,7 +876,7 @@ async fn worker_main(args: WorkerArgs) {
         io::write_msg(
             &mut send,
             &Hello {
-                abi_version: crate::ABI_VERSION,
+                abi_version: crate::WIRE_VERSION,
                 mode,
                 compositor,
                 gamepad,

crates/punktfunk-core/src/lib.rs

@@ -54,3 +54,11 @@ pub use stats::Stats;
 /// v3: added `punktfunk_wake_on_lan` (Wake-on-LAN magic packet; the host's wake MAC(s) reach
 /// clients out-of-band via the mDNS `mac` TXT record, so no connection is required to wake).
 pub const ABI_VERSION: u32 = 3;
+
+/// The punktfunk/1 **wire** version — what `Hello`/`Welcome` carry and hosts equality-check.
+/// Deliberately its own constant: [`ABI_VERSION`] tracks the embeddable **C surface**
+/// (functions a client links), which can grow without changing a single wire byte — v3's
+/// `punktfunk_wake_on_lan` is client-local, and riding the C-ABI bump onto the wire locked
+/// every new client out of every deployed host ("ABI mismatch: client 3 host 2", observed
+/// live). Bump this ONLY when the handshake/planes actually change incompatibly.
+pub const WIRE_VERSION: u32 = 2;

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 +286,15 @@ fn open_gs_virtual_source(
             std::sync::atomic::AtomicBool::new(false),
         ))
     });
-    let vout = vd
-        .create(punktfunk_core::Mode {
+    let vout = crate::vdisplay::registry::acquire(
+        &mut vd,
+        punktfunk_core::Mode {
             width: cfg.width,
             height: cfg.height,
             refresh_hz: cfg.fps,
-        })
-        .context("create virtual output at client resolution")?;
+        },
+    )
+    .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 +399,20 @@ 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)
+}
+
 /// 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 +430,14 @@ 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.
-            const PACE_CHUNK: usize = 16;
+            // Chunk pacing: spread the frame's packets across the send budget in a BOUNDED number
+            // 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 +456,21 @@ 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).
-                    let target = start + per_chunk.mul_f64((i + 1) as f64);
+                    // Sleep toward the next step's deadline; skip sub-500µs sleeps (jitter).
+                    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);
@@ -580,6 +606,15 @@ 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;
+
     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 +680,7 @@ 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;
@@ -654,17 +690,33 @@ 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.
+        let mut want_keyframe = 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();
@@ -889,4 +941,24 @@ 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/mgmt.rs

@@ -156,6 +156,10 @@ 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!(get_status))
                 .routes(routes!(get_local_summary))
                 .routes(routes!(list_paired_clients))
@@ -210,6 +214,7 @@ 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"),
@@ -954,6 +959,242 @@ 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 (e.g. `keep_alive`, `topology`). The remaining
+    /// stored options (`mode_conflict`, `identity`, `layout`) land in later stages — surfaced so the
+    /// console can mark them "coming soon" instead of implying they already take effect.
+    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()],
+    }
+}
+
+/// 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` is rejected until the
+/// display-lifecycle stage ships (it would keep physical monitors dark indefinitely with no release
+/// path yet).
+#[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 = "An option value is not yet supported (e.g. keep_alive forever)", 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 {
+    use crate::vdisplay::policy::KeepAlive;
+    // Reject options this build can't honor yet, so the console can't promise a behavior that won't
+    // happen. `keep_alive: forever` (directly or via the `gaming-rig` preset) needs the Pinned
+    // lifecycle + a release path; until then it would strand physical monitors dark.
+    if policy.effective().keep_alive == KeepAlive::Forever {
+        return api_error(
+            StatusCode::BAD_REQUEST,
+            "keep_alive `forever` (and the `gaming-rig` preset) is not available yet — it arrives \
+             with the display-lifecycle stage. Use a fixed duration for now.",
+        );
+    }
+    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>,
+}
+
+/// 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,
+            })
+            .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 })
+}
+
 /// Live host status
 #[utoipa::path(
     get,
@@ -2257,6 +2498,7 @@ mod tests {
             fps: 120,
             appid: 1,
             peer_ip: None,
+            owner_fp: None,
         });
         state.streaming.store(true, Ordering::SeqCst);
 
@@ -2383,6 +2625,7 @@ mod tests {
             fps: 60,
             appid: 1,
             peer_ip: None,
+            owner_fp: None,
         });
 
         let del = axum::http::Request::delete("/api/v1/session")
@@ -2473,6 +2716,74 @@ mod tests {
             .unwrap()
     }
 
+    /// The display-management endpoints: GET returns the policy surface (presets + effective +
+    /// the Stage-0 enforced list); PUT rejects `keep_alive: forever` (the `gaming-rig` preset)
+    /// *before* persisting, so this stays read-only against the global policy store.
+    #[tokio::test]
+    async fn display_settings_surface_and_forever_rejected() {
+        let app = test_app(test_state(), None);
+
+        let (status, body) = send(&app, get_req("/api/v1/display/settings")).await;
+        assert_eq!(status, StatusCode::OK);
+        assert_eq!(
+            body["presets"].as_array().map(|a| a.len()),
+            Some(5),
+            "all five named presets are surfaced for the console picker"
+        );
+        assert!(
+            body["effective"]["keep_alive"].is_object(),
+            "the effective policy is echoed"
+        );
+        let enforced: Vec<&str> = body["enforced"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .filter_map(|v| v.as_str())
+            .collect();
+        assert!(enforced.contains(&"keep_alive") && enforced.contains(&"topology"));
+
+        // `gaming-rig` expands to keep_alive: forever → rejected at Stage 0 (before any write).
+        let put = axum::http::Request::put("/api/v1/display/settings")
+            .header("content-type", "application/json")
+            .body(Body::from(
+                serde_json::json!({ "preset": "gaming-rig" }).to_string(),
+            ))
+            .unwrap();
+        let (status, body) = send(&app, put).await;
+        assert_eq!(status, StatusCode::BAD_REQUEST);
+        assert!(
+            body["error"]
+                .as_str()
+                .unwrap_or_default()
+                .contains("forever"),
+            "the rejection names the unsupported option"
+        );
+    }
+
+    /// 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

@@ -341,6 +341,11 @@ 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;
+
 /// 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.
@@ -585,10 +590,10 @@ async fn serve_session(
         // the `handshake` future re-decodes for the real session — a few dozen bytes, negligible.
         let gate_hello = Hello::decode(&first).map_err(|e| anyhow!("Hello decode: {e:?}"))?;
         anyhow::ensure!(
-            gate_hello.abi_version == punktfunk_core::ABI_VERSION,
-            "ABI mismatch: client {} host {}",
+            gate_hello.abi_version == punktfunk_core::WIRE_VERSION,
+            "wire version mismatch: client {} host {}",
             gate_hello.abi_version,
-            punktfunk_core::ABI_VERSION
+            punktfunk_core::WIRE_VERSION
         );
         let fp = endpoint::peer_fingerprint(&conn);
         let known = fp
@@ -652,12 +657,12 @@ async fn serve_session(
     let source = opts.source;
     let frames = opts.frames;
     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::ABI_VERSION,
-            "ABI mismatch: client {} host {}",
+            hello.abi_version == punktfunk_core::WIRE_VERSION,
+            "wire version mismatch: client {} host {}",
             hello.abi_version,
-            punktfunk_core::ABI_VERSION
+            punktfunk_core::WIRE_VERSION
         );
         // The pairing gate (require_pairing → paired? else park for delegated approval) ran above,
         // before this future, so a client reaching here is paired (or the host is `--open`).
@@ -684,6 +689,50 @@ 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, Admission};
+            match admit(endpoint::peer_fingerprint(&conn)) {
+                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")?;
 
@@ -805,7 +854,7 @@ async fn serve_session(
         let mut key = [0u8; 16];
         rand::thread_rng().fill_bytes(&mut key);
         let welcome = Welcome {
-            abi_version: punktfunk_core::ABI_VERSION,
+            abi_version: punktfunk_core::WIRE_VERSION,
             udp_port,
             mode: hello.mode,
             // The post-GameStream point of punktfunk/1: Leopard GF(2¹⁶) FEC + real encryption.
@@ -1055,6 +1104,22 @@ async fn serve_session(
         });
     }
 
+    // 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
@@ -3508,7 +3573,11 @@ fn build_pipeline(
     bit_depth: u8,
     plan: crate::session_plan::SessionPlan,
 ) -> 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.
+    let vout = crate::vdisplay::registry::acquire(vd, mode).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

crates/punktfunk-host/src/vdisplay.rs

@@ -403,21 +403,11 @@ 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
-    // the panels + windows land on the streamed surface, not an unstreamed real output (the
-    // auto-detected desktop path *is* "stream this desktop"). Default-on for the auto path; an
-    // explicit `PUNKTFUNK_{KWIN,MUTTER}_VIRTUAL_PRIMARY` still wins.
-    match active.kind {
-        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");
-        }
-        _ => {}
-    }
+    // Topology (Stage 2): the per-compositor backends (KWin/Mutter) now read
+    // [`effective_topology`] directly at create time — the console policy, else the legacy
+    // `PUNKTFUNK_{KWIN,MUTTER}_VIRTUAL_PRIMARY` env, else the Auto default (exclusive on the
+    // auto-desktop path). So this connect-path no longer writes that env (one fewer process-env
+    // mutation on the `ENV_LOCK` surface); `effective_topology()` computes the identical result.
 }
 #[cfg(not(target_os = "linux"))]
 pub fn apply_session_env(_active: &ActiveSession) {}
@@ -723,14 +713,82 @@ 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;
+
+/// 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")]
-#[path = "vdisplay/windows/identity.rs"]
+// Platform-neutral per-client stable display-id map (Stage 3): Windows seeds the monitor EDID +
+// 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 +1,239 @@
+//! 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())
+}
+
+/// 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 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/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 +67,19 @@ 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
-/// its own Wayland connection/thread that owns the resulting output.
-pub struct KwinDisplay;
+/// The KWin virtual-display driver. Carries the connecting client's cert fingerprint (set before
+/// [`create`](VirtualDisplay::create)) so a paired client gets a STABLE per-slot output NAME
+/// (`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]>,
+}
 
 impl KwinDisplay {
     pub fn new() -> Result<Self> {
-        Ok(KwinDisplay)
+        Ok(KwinDisplay::default())
     }
 }
 
@@ -82,14 +88,32 @@ impl VirtualDisplay for KwinDisplay {
         "kwin"
     }
 
+    fn set_client_identity(&mut self, fingerprint: Option<[u8; 32]>) {
+        self.client_fp = fingerprint;
+    }
+
     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 name = match crate::vdisplay::identity::resolve_slot(
+            self.client_fp,
+            (mode.width, mode.height),
+            crate::vdisplay::policy::Identity::Shared,
+        ) {
+            Some(id) => format!("{VOUT_NAME}-{id}"),
+            None => VOUT_NAME.to_string(),
+        };
         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)) {
@@ -107,18 +131,23 @@ 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
-        // stream, not on the headless session's `kwin --virtual` bootstrap output (otherwise the
-        // client sees only the wallpaper of an empty extended output). Opt-in
-        // (PUNKTFUNK_KWIN_VIRTUAL_PRIMARY), mirroring the Mutter backend's PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY.
-        let restore = if virtual_primary_enabled() {
-            apply_virtual_primary()
-        } else {
-            Vec::new()
+        // Display-management topology (Stage 2): `Extend` leaves the streamed output an extension;
+        // `Primary` makes it the primary output but keeps the bootstrap/physical outputs enabled;
+        // `Exclusive` makes it the SOLE desktop (others disabled, restored on teardown) — so
+        // plasmashell + windows land on the streamed surface, not the headless `kwin --virtual`
+        // bootstrap output. Read from the policy (replacing the PUNKTFUNK_KWIN_VIRTUAL_PRIMARY boolean).
+        use crate::vdisplay::policy::Topology;
+        let restore = match crate::vdisplay::effective_topology() {
+            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(),
         };
         Ok(VirtualOutput {
             node_id,
@@ -135,8 +164,8 @@ impl VirtualDisplay for KwinDisplay {
 /// 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 {
-    let output = format!("Virtual-{VOUT_NAME}");
+fn set_custom_refresh(width: u32, height: u32, hz: u32, name: &str) -> u32 {
+    let output = format!("Virtual-{name}");
     let mhz = hz.saturating_mul(1000);
     let run = |arg: String| {
         std::process::Command::new("kscreen-doctor")
@@ -213,26 +242,17 @@ 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
-/// competing output (or one that wants the bootstrap kept) is unaffected; the headless KDE appliance
-/// (run-headless-kde.sh's `kwin --virtual` bootstrap + our streamed output) sets it so the desktop
-/// renders on the streamed surface, not the bootstrap. Mirrors the Mutter backend's gate.
-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)
-}
+/// The prefix EVERY managed KWin output shares — Stage 3 names them `punktfunk` / `punktfunk-<id>`,
+/// which KWin exposes as `Virtual-punktfunk` / `Virtual-punktfunk-<id>`. Group membership (§6.1) is
+/// recognised by this prefix, so we never have to thread the live set through the backend.
+const MANAGED_PREFIX: &str = "Virtual-punktfunk";
 
-/// Names of currently-ENABLED outputs other than our `Virtual-punktfunk` — i.e. the headless
-/// session's bootstrap output(s), which hold the desktop by default. Parsed from `kscreen-doctor -j`
-/// (same source as [`read_active_refresh`]).
+/// Names of currently-ENABLED outputs that are **not managed by us** — the headless session's
+/// bootstrap output(s) + any physical monitor, i.e. exactly what `exclusive` must disable.
+/// **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 +268,49 @@ fn other_enabled_outputs() -> Vec<String> {
         .and_then(|o| o.as_array())
         .map(|outs| {
             outs.iter()
-                .filter(|o| {
-                    o.get("enabled").and_then(|e| e.as_bool()).unwrap_or(false)
-                        && o.get("name").and_then(|n| n.as_str()) != Some(ours.as_str())
-                })
-                .filter_map(|o| o.get("name").and_then(|n| n.as_str()).map(String::from))
+                .filter(|o| o.get("enabled").and_then(|e| e.as_bool()).unwrap_or(false))
+                .filter_map(|o| o.get("name").and_then(|n| n.as_str()))
+                .filter(|n| !n.starts_with(MANAGED_PREFIX))
+                .map(String::from)
                 .collect()
         })
         .unwrap_or_default()
 }
 
-/// Set `Virtual-punktfunk` primary and disable the bootstrap output(s) so it 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
+/// True if any managed group member (the [`MANAGED_PREFIX`] family) is ALREADY the KWin primary —
+/// first-slot-wins support (§6.1) so a later exclusive session doesn't steal primary from the group's
+/// 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> {
-    let ours = format!("Virtual-{VOUT_NAME}");
+fn apply_virtual_primary(name: &str) -> Vec<String> {
+    let ours = format!("Virtual-{name}");
     let kscreen = |args: &[String]| {
         std::process::Command::new("kscreen-doctor")
             .args(args)
@@ -271,15 +318,20 @@ 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
-    // own. Let that settle, then belt-and-suspenders: disable anything still enabled besides ours so
-    // the streamed output is unambiguously the sole desktop regardless of KWin's implicit behaviour.
-    if !kscreen(&[format!("output.{ours}.primary")]) {
-        tracing::warn!(
-            "KWin: could not set the virtual output primary; client may see only the wallpaper"
-        );
+    // First-slot-wins (§6.1): only grab primary if no managed group member is primary yet — so a 2nd
+    // exclusive session joins as a secondary monitor of the shared desktop instead of stealing the
+    // shell off the 1st session's output. KWin usually then re-homes the desktop + disables the
+    // bootstrap on its own; the belt-and-suspenders disable below covers the rest.
+    if !a_managed_output_is_primary() {
+        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
@@ -292,6 +344,23 @@ 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.
 struct StopGuard {
@@ -388,10 +457,11 @@ 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 +501,7 @@ pub fn is_available() -> bool {
 fn run(
     width: u32,
     height: u32,
+    name: &str,
     setup_tx: &Sender<Result<u32, String>>,
     stop: &AtomicBool,
 ) -> Result<()> {
@@ -453,7 +524,7 @@ 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 +593,27 @@ 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

@@ -118,9 +118,19 @@ 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
-        // new (virtual) connector apart and restore the layout on teardown. Best-effort.
-        let dc_pre = if virtual_primary_enabled() {
+        // Display-management topology (Stage 2): the console policy's level, resolved to a concrete
+        // value. `Extend` leaves the virtual output an extension (no config change); `Primary` makes
+        // 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.
+        let topo = crate::vdisplay::effective_topology();
+        let want_config = matches!(
+            topo,
+            crate::vdisplay::policy::Topology::Primary | crate::vdisplay::policy::Topology::Exclusive
+        );
+        let exclusive = matches!(topo, crate::vdisplay::policy::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 +162,12 @@ 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 {
-                Ok(()) => tracing::info!("mutter: virtual output set as the primary monitor"),
+            match make_virtual_primary(dc, mode, pre, exclusive).await {
+                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 +352,6 @@ 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 +414,12 @@ 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 +445,14 @@ 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 +474,12 @@ 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
-/// disables them for the session. This confines the cursor, windows, and keyboard focus to the
+/// **Exclusive** — the virtual output as the SOLE, primary monitor: physical outputs are omitted, so
+/// 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 +489,47 @@ 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 +1,573 @@
+//! 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
+    }
+}
+
+/// 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 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 +1,418 @@
+//! 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>,
+}
+
+/// The live display set for the mgmt `/display/state` endpoint.
+#[derive(Clone, Debug, Default)]
+pub struct Snapshot {
+    pub displays: Vec<DisplayInfo>,
+}
+
+/// 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.
+pub fn acquire(
+    vd: &mut Box<dyn super::VirtualDisplay>,
+    mode: super::Mode,
+) -> Result<super::VirtualOutput> {
+    #[cfg(target_os = "linux")]
+    {
+        linux::acquire(vd, mode)
+    }
+    #[cfg(not(target_os = "linux"))]
+    {
+        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")]
+    {
+        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,
+            })
+            .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::{AtomicU64, Ordering};
+    use std::sync::{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, 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,
+        /// 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,
+    }
+
+    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.
+    fn take_expired(entries: &mut Vec<Entry>, now: Instant) -> Vec<Entry> {
+        let mut expired = Vec::new();
+        let mut i = 0;
+        while i < entries.len() {
+            if entries[i].life.poll_expiry(now) {
+                expired.push(entries.remove(i));
+            } else {
+                i += 1;
+            }
+        }
+        expired
+    }
+
+    /// 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 = {
+                        let mut es = reg().entries.lock().unwrap();
+                        take_expired(&mut es, Instant::now())
+                    };
+                    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,
+    ) -> VirtualOutput {
+        VirtualOutput {
+            node_id,
+            remote_fd: None,
+            preferred_mode,
+            keepalive: Box::new(DisplayLease { gen }),
+        }
+    }
+
+    pub(super) fn acquire(vd: &mut Box<dyn VirtualDisplay>, mode: Mode) -> Result<VirtualOutput> {
+        ensure_timer();
+        let backend = vd.name();
+        let r = reg();
+
+        // Reap expired first (drop outside the lock).
+        let expired = {
+            let mut es = r.entries.lock().unwrap();
+            take_expired(&mut es, Instant::now())
+        };
+        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);
+                tracing::info!(
+                    backend,
+                    node_id = e.node_id,
+                    "virtual display reused (keep-alive reconnect)"
+                );
+                return Ok(out);
+            }
+        }
+
+        // Create a fresh display (NOT under the lock — `vd.create` blocks + spawns threads).
+        let real = vd.create(mode)?;
+
+        // 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;
+        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,
+            gen,
+        };
+        r.entries.lock().unwrap().push(entry);
+        Ok(output_for(node_id, preferred_mode, gen))
+    }
+
+    /// 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) {
+        let Some(r) = REG.get() else { return };
+        let linger = linger();
+        let torn_down = {
+            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 => Some(es.remove(idx)),
+                Release::Linger => {
+                    tracing::info!(
+                        backend = es[idx].backend,
+                        "virtual display: last session left — lingering (keep-alive)"
+                    );
+                    None
+                }
+                Release::Pin => {
+                    tracing::info!(
+                        backend = es[idx].backend,
+                        "virtual display: last session left — pinned (keep-alive forever)"
+                    );
+                    None
+                }
+                // Linux entries are single-session (refs == 1), so Decref never occurs; harmless.
+                Release::Decref => None,
+            }
+        };
+        if let Some(e) = torn_down {
+            tracing::info!(
+                backend = e.backend,
+                "virtual display torn down (keep-alive off / released)"
+            );
+            drop(e); // outside the lock — the keepalive Drop may block
+        }
+    }
+
+    pub(super) fn snapshot() -> Vec<DisplayInfo> {
+        let Some(r) = REG.get() else {
+            return Vec::new();
+        };
+        let now = Instant::now();
+        r.entries
+            .lock()
+            .unwrap()
+            .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),
+                    // Idle entries are never stored (removed on teardown).
+                    lifecycle::State::Idle => return None,
+                };
+                Some(DisplayInfo {
+                    slot: e.gen,
+                    backend: e.backend.to_string(),
+                    mode: (e.mode.width, e.mode.height, e.mode.refresh_hz),
+                    state: state.to_string(),
+                    expires_in_ms,
+                    sessions,
+                    client: None,
+                })
+            })
+            .collect()
+    }
+
+    pub(super) fn force_release(slot: Option<u64>) -> usize {
+        let Some(r) = REG.get() else { return 0 };
+        let released = {
+            let mut es = r.entries.lock().unwrap();
+            let mut out = 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() {
+                    out.push(es.remove(i));
+                } else {
+                    i += 1;
+                }
+            }
+            out
+        };
+        let n = released.len();
+        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,
+    }
+
+    impl Drop for DisplayLease {
+        fn drop(&mut self) {
+            release(self.gen);
+        }
+    }
+}

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
@@ -169,10 +169,10 @@ 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
-    /// connecting client's id here, so the client keeps the same EDID serial + IddCx ConnectorIndex across
-    /// reconnects and Windows reapplies its saved per-monitor config (DPI scaling). See [`super::identity`].
-    identity_map: Mutex<super::identity::MonitorIdentityMap>,
+    // The per-client stable monitor-id map is now the process-wide `super::identity::global()`
+    // (shared with the Linux KWin backend's per-slot naming — never same-process). A monitor CREATE
+    // resolves the client's id via `identity::resolve_slot`, so it keeps the same EDID serial + IddCx
+    // ConnectorIndex across reconnects and Windows reapplies its saved per-monitor DPI scaling.
 }
 
 static VDM: OnceLock<VirtualDisplayManager> = OnceLock::new();
@@ -188,7 +188,6 @@ 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()),
     })
 }
 
@@ -527,10 +526,14 @@ 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).
-        let preferred_id = client_fp
-            .map(|fp| self.identity_map.lock().unwrap().resolve(fp))
-            .unwrap_or(0);
+        // auto-allocates the lowest-free id (the original slot-based behavior). The `identity` policy
+        // picks per-client vs per-client-mode; Windows defaults to PerClient (its historical behavior).
+        let preferred_id = super::identity::resolve_slot(
+            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 +633,36 @@ 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
-                // isn't DWM-composited on this box → Desktop Duplication born-losts. Deactivating the other
-                // display(s) first via the atomic CCD path promotes the IDD to a composited primary with no
-                // MODE_CHANGE storm. Opt out with PUNKTFUNK_NO_ISOLATE=1.
-                if std::env::var("PUNKTFUNK_NO_ISOLATE").is_err() {
-                    // SAFETY: `isolate_displays_ccd` is `unsafe` for its CCD topology FFI; it takes a
-                    // `Copy` `u32` by value and returns an owned `SavedConfig` snapshot (no borrowed
-                    // memory crosses). It runs under the `state` lock, the sole mutator of the topology.
-                    ccd_saved = unsafe { isolate_displays_ccd(added.target_id) };
-                } else {
-                    tracing::info!("display isolation skipped (PUNKTFUNK_NO_ISOLATE) — IDD stays extended");
+                // Apply the display-management topology (Stage 2). `Exclusive` (default) deactivates the
+                // other display(s) so the IDD is the SOLE composited primary — an EXTENDED (non-primary)
+                // IDD isn't DWM-composited on this box → Desktop Duplication born-losts. `Primary` keeps the
+                // physical display(s) ACTIVE and makes the IDD primary (repositioned to origin). `Extend`
+                // leaves it a plain extension. Both isolate + primary go through the atomic CCD path (no
+                // MODE_CHANGE storm). Opt out (extend) with PUNKTFUNK_NO_ISOLATE=1 / the console policy.
+                use crate::vdisplay::policy::Topology;
+                match topology_action() {
+                    // SAFETY (both arms): the CCD helper is `unsafe` for its topology FFI; it takes a
+                    // `Copy` `u32` by value and returns an owned `SavedConfig` (no borrowed memory crosses),
+                    // 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
             }
@@ -890,10 +912,124 @@ 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"`.
+    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))
+            }
+        };
+        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 LINGERING monitor now (the `/display/release` endpoint) — so a
+    /// physical-screen user gets their screen back without waiting out the linger. An Active monitor
+    /// is refused (stopping a live session is session management, not display management). Returns
+    /// `true` if a lingering 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 { .. }) {
+            if let MgrState::Lingering { mon, .. } = std::mem::replace(&mut *st, MgrState::Idle) {
+                // 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 `Lingering` 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,
+            // Pinned (keep forever) is built in the display-lifecycle stage; until then fall back to
+            // the default rather than silently keeping the monitor — and thus the physical screens —
+            // dark indefinitely. (The mgmt PUT also rejects `forever` at Stage 0, so this is defensive.)
+            Linger::Forever => {
+                tracing::warn!(
+                    "display policy: keep_alive=forever not yet honored — lingering 10 s \
+                     (Pinned lands in the display-lifecycle stage)"
+                );
+                10_000
+            }
+        };
+    }
     std::env::var("PUNKTFUNK_MONITOR_LINGER_MS")
         .ok()
         .and_then(|s| s.parse().ok())
         .unwrap_or(10_000)
 }
+
+/// 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, mut 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() {
-        if p.targetInfo.id == keep_target_id {
+
+    // The virtual output's source width, to lay the other displays out to its right.
+    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 {
-            p.flags &= !DISPLAYCONFIG_PATH_ACTIVE; // mark this path inactive
-            others += 1;
+        let Some(m) = modes.get_mut(idx) else {
+            continue;
+        };
+        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)
 }

design/display-management.md

@@ -0,0 +1,782 @@
+# Virtual-display management & lifecycle policy — design
+
+> **Status (2026-07-05):** **Stages 0–4 DONE + on-glass validated; Stage 5 STARTED** (branch
+> `display-mgmt-stage0`, not yet merged). See the **Status — handoff** block under §11 for the
+> per-stage state, the key decisions (notably the Windows `reject` default), and what's left.
+> 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 new `Pinned` state.
+
+**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** (GameStream `cancel`/quit-app; a future punktfunk/1
+  `EndSession{quit}` control message — protocol growth, trailing-byte back-compat as usual)
+  bypasses keep-alive: the user said "stop the game", so tear down now. Plain disconnects and
+  connection losses honor the policy.
+- 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; add `Pinned` |
+| 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: STARTED** — only the critical §6.1 **group-aware exclusive** fix for KWin has landed
+  (`kwin.rs` `MANAGED_PREFIX` + first-slot-wins), unit-tested but NOT yet driven by two concurrent
+  sessions on-glass. Everything else in Stage 5 is TODO.
+
+**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).
+
+**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`**; the KWin
+set-150 %-scaling ROUND-TRIP (SSH can't drive `kscreen-doctor` into the live session — the persist
+mechanism itself is already proven); GameStream 503 on-glass; two-concurrent-session validation of the
+Stage-5 group-aware exclusive.
+
+- **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.
+  *Validate on KDE:* connect client A → set 150 % scaling → disconnect → reconnect → scaling
+  reapplied; client B unaffected; `kwinoutputconfig.json` inspected for the named entries.
+- **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. [STARTED]** 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 so far:** 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. **TODO:** Mutter + wlroots group-aware analogues (Mutter is more involved — its
+  sole-monitor `ApplyMonitorsConfig` must include ALL group virtuals, not just its own); layout
+  auto-row + manual + `/display/layout` + console table; per-group topology restore (restore the
+  physical only when the group's LAST member drops); gamescope groups (single-output → decline extras).
+  *Validate:* two clients (probe + GTK) on the headless KDE box forming a 2-output desktop;
+  drag a window across; disconnect one → its slot lingers per policy, sibling unaffected,
+  restore only after both drop.
+- **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/arch.md

@@ -0,0 +1,134 @@
+---
+title: Arch Linux
+description: Install a punktfunk host on Arch (and Arch-derived distros) from the signed pacman binary repo.
+---
+
+Set up a punktfunk host on **Arch Linux** (or an Arch-derived distro like CachyOS/EndeavourOS). The
+host installs from a **signed pacman binary repo**, so it updates with `pacman -Syu` like the rest
+of your system — no building required. Host encode is **NVENC on NVIDIA** and **VAAPI on
+AMD/Intel** (`PUNKTFUNK_ENCODER=auto` picks per GPU).
+
+> New here? Read [Security & Safe Use](/docs/security) first — a streaming host is remote control of
+> the machine, so keep it on a trusted LAN or VPN and require pairing.
+
+> Prefer to build it yourself? A split `PKGBUILD` (host + client + optional web console) is in the
+> repo at `packaging/arch/` — see the [appendix](#appendix--build-from-source-pkgbuild). The binary
+> repo below is the supported path.
+
+## 1. GPU prerequisites
+
+- **NVIDIA:** `sudo pacman -S --needed nvidia-utils` (provides NVENC + the EGL/CUDA zero-copy path).
+  Arch's stock `ffmpeg` already has NVENC built in — no RPM-Fusion-style swap like Fedora needs.
+- **AMD / Intel:** the Mesa stack (`mesa`, `libva-mesa-driver` for AMD, `intel-media-driver` for
+  Intel) provides the VAAPI encoder — usually already installed on a desktop.
+
+## 2. Add the signed repo
+
+The registry **signs its database and every package**, so first trust its key once (after this,
+packages install signature-verified):
+
+```sh
+# Trust the registry signing key.
+curl -fsS https://git.unom.io/api/packages/unom/arch/repository.key \
+  | sudo pacman-key --add -
+sudo pacman-key --lsign-key E0CA04465C99C936E0B0C6510A317015A34DDD69
+
+# Add the repo (append to /etc/pacman.conf). No SigLevel line needed — pacman's default
+# verifies signed packages against the key you just trusted.
+sudo tee -a /etc/pacman.conf >/dev/null <<'EOF'
+
+[punktfunk]
+Server = https://git.unom.io/api/packages/unom/arch/$repo/$arch
+EOF
+```
+
+> **Stable vs canary.** `[punktfunk]` is the **stable** channel — it moves only when a `vX.Y.Z`
+> release is cut. For the latest `main` build, use `[punktfunk-canary]` instead (same `Server` line,
+> just the repo name). Enable exactly one. See [Release Channels](/docs/channels).
+
+## 3. Install the host
+
+```sh
+sudo pacman -Sy punktfunk-host      # the streaming host
+sudo pacman -S  punktfunk-web       # optional: the browser management console (pairing + status)
+sudo usermod -aG input "$USER"      # /dev/uinput access for virtual gamepads (re-login to apply)
+```
+
+`punktfunk-client` (the GTK4 couch/Deck client) is in the same repo if this box is also a client.
+The host package ships the systemd **user** units, the udev rule, the UDP socket-buffer sysctl
+tuning, and example configs. Updates later are just `sudo pacman -Syu`.
+
+## 4. Configure and run
+
+The host runs as a systemd **`--user`** service — it needs your session's PipeWire and D-Bus.
+Copy a starting config, enable the service, and enable linger so it starts at boot without a login:
+
+```sh
+mkdir -p ~/.config/punktfunk
+cp /usr/share/punktfunk/host.env.example ~/.config/punktfunk/host.env   # then edit
+systemctl --user daemon-reload
+systemctl --user enable --now punktfunk-host
+sudo loginctl enable-linger "$USER"
+```
+
+Which compositor the host captures depends on your desktop — it drives a per-client virtual output
+via KWin (Plasma), Mutter (GNOME), or wlroots (Sway), or spawns a headless **gamescope** session
+per connect. For a headless appliance, the package also ships `punktfunk-kde-session.service`
+(a dedicated `kwin --virtual` session, same as the [Fedora KDE](/docs/fedora-kde#3-kwin-streaming-session)
+guide — `cp /usr/share/punktfunk/host.env.kde ~/.config/punktfunk/host.env` and enable it alongside
+the host). See [Configuration](/docs/configuration) for every knob and
+[Running as a Service](/docs/running-as-a-service) for the service model.
+
+Check it came up:
+
+```sh
+systemctl --user status punktfunk-host          # active
+journalctl --user -u punktfunk-host -f          # watch a client connect
+```
+
+### Web console
+
+The console (status, paired devices, arm pairing) ships as `punktfunk-web` — enable it, then open
+`http://<host-ip>:47992`:
+
+```sh
+systemctl --user enable --now punktfunk-web
+```
+
+#### Console login password
+
+On first start `punktfunk-web-init` generates a random login password and saves it to
+`~/.config/punktfunk/web-password` (as `PUNKTFUNK_UI_PASSWORD=…`). Read it back at any time:
+
+```sh
+journalctl --user -u punktfunk-web-init | sed -n 's/.*password generated: //p'
+sed -n 's/^PUNKTFUNK_UI_PASSWORD=//p' ~/.config/punktfunk/web-password
+```
+
+To set your own, edit that file and `systemctl --user restart punktfunk-web`. Forgot it? See
+[Forgot your Password?](/docs/forgot-password).
+
+## 5. Connect a client
+
+From any [client](/docs/clients), `--discover` finds the host on the LAN. On first connect, complete
+the **PIN pairing** — arm it from the host's web console, which displays a 4-digit PIN to type into
+the client. (Pairing is required by default; pass `serve --open` only if you deliberately want to
+disable it.) See [Clients](/docs/clients) and [Pairing](/docs/pairing).
+
+## Appendix — build from source (PKGBUILD)
+
+To build instead of using the binary repo, use the split `PKGBUILD` in `packaging/arch/` (produces
+`punktfunk-host` + `punktfunk-client`; set `PF_WITH_WEB=1` to also build `punktfunk-web`, which needs
+`bun`):
+
+```sh
+git clone https://git.unom.io/unom/punktfunk.git && cd punktfunk/packaging/arch
+# Build the working tree (no git fetch):
+PF_SRCDIR="$(git rev-parse --show-toplevel)" makepkg -f --holdver
+sudo pacman -U punktfunk-host-*.pkg.tar.zst
+```
+
+NVENC/EGL come from the NVIDIA driver (`nvidia-utils`); on a GPU-less builder, symlink the CUDA
+stub into the link path first (the `PKGBUILD` header documents this). Full details, the
+Fedora→Arch dependency map, and the SteamOS systemd-sysext path are in
+[`packaging/arch/README.md`](https://git.unom.io/unom/punktfunk/src/branch/main/packaging/arch/README.md).

docs-site/content/docs/bazzite.md

@@ -24,36 +24,43 @@ mid-stream. You flip between Gaming Mode and Desktop with Bazzite's normal Steam
 
 ## Install
 
-The host ships as an RPM in punktfunk's **Gitea RPM registry** (public), so a Bazzite / Fedora
-Atomic box layers and updates it with `rpm-ostree`. Add the repo, then layer the host plus the web
-console and reboot:
+The host installs as a **systemd system extension (sysext)** — no `rpm-ostree` layering. The
+Bazzite docs treat layering as a last resort (layered packages slow every OS update and can block
+upgrades until removed); a sysext never enters an rpm-ostree transaction: it overlays `/usr`
+read-only from `/var/lib/extensions/`, survives OS updates, installs and updates **without a
+reboot**, and is removable in one command. This is the same mechanism the Fedora Atomic
+maintainers ship via the [fedora-sysexts](https://fedora-sysexts.github.io/) project.
 
 ```sh
-# Add the repo. Packages are GPG-signed (gpgcheck=1, the packages@unom.io key) AND the repo
-# metadata is Gitea-signed (repo_gpgcheck=1); gpgkey lists both keys so dnf imports each.
-sudo tee /etc/yum.repos.d/punktfunk.repo >/dev/null <<'REPO'
-[gitea-unom-bazzite]
-name=punktfunk (unom, Bazzite)
-baseurl=https://git.unom.io/api/packages/unom/rpm/bazzite
-enabled=1
-gpgcheck=1
-repo_gpgcheck=1
-gpgkey=https://git.unom.io/api/packages/unom/rpm/repository.key
-       https://git.unom.io/api/packages/unom/generic/punktfunk-keys/1/RPM-GPG-KEY-punktfunk
-REPO
-
-# Layer the host + the web console, then reboot into the new deployment.
-# (punktfunk Recommends punktfunk-web; list it explicitly so it's pulled regardless of weak-dep
-# settings — the Gitea registry carries punktfunk-web, which COPR can't build.)
-rpm-ostree install punktfunk punktfunk-web
-systemctl reboot
+# One-time bootstrap (afterwards the updater is on PATH as `punktfunk-sysext`):
+curl -fsSLO https://git.unom.io/unom/punktfunk/raw/branch/main/packaging/bazzite/punktfunk-sysext.sh
+sudo bash punktfunk-sysext.sh install          # add `--channel canary` for rolling builds
 ```
 
-`rpm-ostree upgrade` then tracks new builds automatically (Bazzite's auto-update timer does this
-for you). For a fully baked appliance image there's also a **bootc** Containerfile that installs
-the same RPMs from this registry — see `packaging/bootc/` and `packaging/rpm/README.md` in the repo.
-Building from source works too (Bazzite is Fedora Atomic underneath, and its FFmpeg builds the host
-fine — same steps as [Fedora KDE](/docs/fedora-kde)), but the registry is the supported path.
+That downloads the newest image (host + tray + web console, SHA-256-verified over HTTPS from
+punktfunk's package registry), merges it, and applies the udev/sysctl setup on the spot — the
+host is usable immediately, no reboot. From then on:
+
+```sh
+sudo punktfunk-sysext update     # fetch + merge the newest build
+sudo punktfunk-sysext status     # channel, installed vs latest version
+sudo punktfunk-sysext remove     # unmerge and delete — the box is back to stock
+```
+
+Two things to know:
+
+- **After a Bazzite major rebase** (Fedora 43 → 44) the old image **refuses to load** rather than
+  run against mismatched system libraries — run `sudo punktfunk-sysext update` once and it fetches
+  the image built for the new base.
+- **Already layering punktfunk?** Install the sysext (it shadows the layered copy immediately),
+  then drop the layer so it stops slowing your updates:
+  `sudo rpm-ostree uninstall punktfunk punktfunk-web && systemctl reboot`.
+
+For a fully baked appliance image there's also a **bootc** Containerfile that installs the RPMs
+from the registry at image-build time — see `packaging/bootc/` in the repo. Plain `rpm-ostree`
+layering from the [RPM registry](https://git.unom.io/unom/-/packages) keeps working too (see
+`packaging/bazzite/README.md`), but the sysext is the supported default. Building from source
+also works (Bazzite is Fedora Atomic underneath — same steps as [Fedora KDE](/docs/fedora-kde)).
 
 ## Allow controller input
 

docs-site/content/docs/channels.md

@@ -25,6 +25,8 @@ track per machine; switching is a one-line change.
 |---|---|---|
 | **apt** (host/client) | `deb [signed-by=…] https://git.unom.io/api/packages/unom/debian canary main` | `… debian stable main` |
 | **rpm** (host) | baseurl `…/rpm/bazzite-canary` (or `fedora-44-canary`) | `…/rpm/bazzite` (or `fedora-44`) |
+| **sysext** (Bazzite host) | `sudo punktfunk-sysext install --channel canary` | `… install` / default (feeds `…/punktfunk-sysext/f43[-canary]`) |
+| **pacman** (Arch host/client) | `[punktfunk-canary]` repo section | `[punktfunk]` (`Server = …/api/packages/unom/arch/$repo/$arch`) |
 | **Flatpak** (client) | `flatpak install --user https://flatpak.unom.io/io.unom.Punktfunk.Canary.flatpakref` | `…/io.unom.Punktfunk.flatpakref` |
 | **Decky** (Steam Deck) | install-from-URL `…/generic/punktfunk-decky/canary/punktfunk.zip` | `…/punktfunk-decky/latest/punktfunk.zip` |
 | **Windows client** (MSIX) | `…/generic/punktfunk-client-windows/canary/punktfunk-client-windows_x64.msix` | `…/latest/…` + the release page |

docs-site/content/docs/clients.md

@@ -47,7 +47,7 @@ It ships as a real package, not just a source build — full steps in
   `flatpak update`; this is also what the [Decky plugin](/docs/steam-deck) launches.
 - **Ubuntu / Debian** — `apt install punktfunk-client` from the punktfunk apt registry.
 - **Fedora / Bazzite** — `rpm-ostree install punktfunk-client` from the Gitea RPM registry.
-- **Arch / SteamOS** — the `punktfunk-client` split package from the `PKGBUILD`.
+- **Arch** — `sudo pacman -Sy punktfunk-client` from the signed binary repo (see [Arch Linux](/docs/arch)).
 
 Launch it, pick your host from the list, and stream. For scripting you can skip the host list and
 connect straight away:

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/install-client.md

@@ -48,7 +48,7 @@ see the linked guide — then it tracks updates with your normal `apt upgrade` /
 |--------|---------|-------|
 | **Ubuntu / Debian** | `sudo apt install punktfunk-client` | [packaging/debian](https://git.unom.io/unom/punktfunk/src/branch/main/packaging/debian/README.md) |
 | **Fedora / Bazzite** | `rpm-ostree install punktfunk-client` | [packaging/rpm](https://git.unom.io/unom/punktfunk/src/branch/main/packaging/rpm/README.md) |
-| **Arch / SteamOS** | `punktfunk-client` from the `PKGBUILD` | [packaging/arch](https://git.unom.io/unom/punktfunk/src/branch/main/packaging/arch/README.md) |
+| **Arch** | `sudo pacman -Sy punktfunk-client` (signed binary repo) | [Arch Linux](/docs/arch) |
 
 Then launch it, pick your host from the list, and stream. For scripting, skip the picker:
 

docs-site/content/docs/install.md

@@ -17,13 +17,14 @@ On **Windows**, the host ships as a signed installer instead — see [Windows](#
 | Distro | Package manager | One-command happy path | Guide |
 |--------|-----------------|------------------------|-------|
 | **Ubuntu / Debian** | apt | `sudo apt install punktfunk-host` | [Ubuntu — GNOME](/docs/ubuntu-gnome) · [Ubuntu — KDE](/docs/ubuntu-kde) · [packaging/debian](https://git.unom.io/unom/punktfunk/src/branch/main/packaging/debian/README.md) |
-| **Fedora / Bazzite** | rpm-ostree | `rpm-ostree install punktfunk punktfunk-web` | [Fedora — KDE](/docs/fedora-kde) · [Bazzite](/docs/bazzite) · [packaging/rpm](https://git.unom.io/unom/punktfunk/src/branch/main/packaging/rpm/README.md) |
-| **Arch** | PKGBUILD | `makepkg -si` | [packaging/arch](https://git.unom.io/unom/punktfunk/src/branch/main/packaging/arch/README.md) |
+| **Bazzite / Fedora Atomic** | systemd-sysext | `sudo bash punktfunk-sysext.sh install` (no layering, no reboot) | [Bazzite](/docs/bazzite) · [packaging/bazzite](https://git.unom.io/unom/punktfunk/src/branch/main/packaging/bazzite/README.md) |
+| **Fedora (dnf)** | dnf / rpm-ostree | `dnf install punktfunk punktfunk-web` | [Fedora — KDE](/docs/fedora-kde) · [packaging/rpm](https://git.unom.io/unom/punktfunk/src/branch/main/packaging/rpm/README.md) |
+| **Arch** | pacman | `pacman -Sy punktfunk-host` (binary repo) | [Arch Linux](/docs/arch) · [packaging/arch](https://git.unom.io/unom/punktfunk/src/branch/main/packaging/arch/README.md) |
 | **SteamOS (host)** | on-device script | `bash scripts/steamdeck/install.sh` | [SteamOS (Host)](/docs/steamos-host) |
 
 Each registry is public — no auth, you just trust the repo's signing key. Adding the repo is a
-one-time step covered in the linked guide; after that, normal `apt upgrade` / `rpm-ostree upgrade`
-tracks new builds automatically.
+one-time step covered in the linked guide; after that, normal `apt upgrade` / `dnf upgrade` /
+`pacman -Syu` (or `sudo punktfunk-sysext update` on Bazzite) tracks new builds.
 
 > **Stable vs canary.** The repos in the per-distro guides are the **stable** channel — it only
 > moves when a `vX.Y.Z` release is cut. For the latest `main` build (fast, possibly broken), point
@@ -59,7 +60,8 @@ fallback without one. More detail — including the CLI `punktfunk-host service
 
 - **`punktfunk-host`** — the streaming host. Install this on your Linux gaming machine.
 - **`punktfunk-web`** — the browser management console (pairing + status). Recommended alongside the
-  host; on RPM list it explicitly (`rpm-ostree install punktfunk punktfunk-web`).
+  host; on RPM list it explicitly (`dnf install punktfunk punktfunk-web`) — the Bazzite sysext
+  image already includes it.
 - **`punktfunk-client`** — the GTK4 desktop client, for streaming *to* a Linux box (also shipped via
   apt / RPM / Arch / Flatpak). On a Steam Deck, this is the package you want.
 

docs-site/content/docs/meta.json

@@ -11,6 +11,7 @@
     "ubuntu-gnome",
     "ubuntu-kde",
     "fedora-kde",
+    "arch",
     "bazzite",
     "steamos-host",
     "windows-host",
@@ -23,6 +24,7 @@
     "pairing",
     "---Configuration---",
     "configuration",
+    "virtual-displays",
     "host-cli",
     "---Troubleshooting---",
     "troubleshooting",

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

@@ -0,0 +1,133 @@
+---
+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:** this release wires **keep-alive** (linger duration) and **topology**
+> (extend / primary / exclusive). The other options below — conflict handling, identity/scaling
+> persistence on Linux, and multi-monitor layout — are **stored but not yet enforced**; they arrive
+> in following releases. The console marks them accordingly. Windows already persists per-client
+> scaling (see [Persistent scaling](#persistent-scaling)).
+
+## 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, and whoever connects takes the box over. *(Arrives with the keep-alive stage.)* |
+| **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. *(Arrives with the
+  keep-alive lifecycle stage; the console won't let you save it before then.)*
+
+Default: **10 seconds**. Windows has always lingered 10 s; the Linux backends previously tore down
+immediately — a short linger makes reconnects smoother on both.
+
+> **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 | ✅ *(following release)* |
+| Exclusive | ✅ | ✅ | ✅ *(following release)* | ✅ |
+
+### Conflict handling · identity · layout
+
+These are **stored but not yet enforced** — they're documented here so you know what's coming and
+can set them ahead of the release that turns them on:
+
+- **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**).
+- **Identity** — whether each client gets a **stable display identity** so your desktop environment
+  remembers its settings (see below): one shared identity, one **per client**, or one **per client +
+  resolution**.
+- **Layout / max displays** — how multiple virtual displays are arranged (for multi-monitor), and an
+  upper bound on how many can be live at once.
+
+## 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** | ⏳ following release | A stable per-client output name lets KWin persist scale/mode per client. |
+| **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`) |
+
+## 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

@@ -21,6 +21,14 @@
 // clients out-of-band via the mDNS `mac` TXT record, so no connection is required to wake).
 #define ABI_VERSION 3
 
+// The punktfunk/1 **wire** version — what `Hello`/`Welcome` carry and hosts equality-check.
+// Deliberately its own constant: [`ABI_VERSION`] tracks the embeddable **C surface**
+// (functions a client links), which can grow without changing a single wire byte — v3's
+// `punktfunk_wake_on_lan` is client-local, and riding the C-ABI bump onto the wire locked
+// every new client out of every deployed host ("ABI mismatch: client 3 host 2", observed
+// live). Bump this ONLY when the handshake/planes actually change incompatibly.
+#define WIRE_VERSION 2
+
 // `PunktfunkHidOutput::kind` — lightbar RGB (`r`/`g`/`b` valid).
 #define PUNKTFUNK_HIDOUT_LED 1
 

packaging/README.md

@@ -17,13 +17,15 @@ packaging/
   rpm/punktfunk.spec      # the RPM (builds punktfunk-host from source with cargo)
   bazzite/host.env        # gamescope-default config for a Bazzite appliance
   bazzite/README.md       # step-by-step Bazzite setup guide
+  bazzite/*sysext*.sh     # the no-layering path: build/install/publish the systemd-sysext
   bootc/Containerfile     # bake punktfunk into a Bazzite-based atomic image
   copr/                   # COPR build-from-SCM settings
 ```
 
 The other packaging targets have their own READMEs: [`debian/`](debian/README.md) (apt),
-[`arch/`](arch/README.md) (PKGBUILD + sysext), [`flatpak/`](flatpak/README.md) (the client),
-[`windows/`](windows/README.md) (host installer + drivers), plus `kde/` and `linux/` helpers.
+[`arch/`](arch/README.md) (pacman binary repo + PKGBUILD + SteamOS sysext),
+[`flatpak/`](flatpak/README.md) (the client), [`windows/`](windows/README.md) (host installer +
+drivers), plus `kde/` and `linux/` helpers.
 
 ## What's needed beyond base Fedora
 
@@ -38,7 +40,22 @@ On **Bazzite** the only genuinely new runtime bits are `ffmpeg-libs` (RPM Fusion
 `libei` — the rest of the stack is already there. The default backend is **gamescope**
 (`packaging/bazzite/host.env`), which the host spawns headless per session — no desktop login.
 
-## Option A — Gitea RPM registry (recommended; per-host, `rpm-ostree`)
+## Option A — systemd-sysext (recommended; no layering, no reboot)
+
+On Bazzite / Fedora Atomic the recommended install is the **systemd-sysext** image — rpm-ostree
+layering is a last resort per the Bazzite docs (it slows every OS update and can block upgrades),
+while a sysext overlays `/usr` at runtime, survives OS updates, and updates in one command with
+no reboot. CI wraps the same RPMs below into the image, so content and channels are identical.
+
+```sh
+curl -fsSLO https://git.unom.io/unom/punktfunk/raw/branch/main/packaging/bazzite/punktfunk-sysext.sh
+sudo bash punktfunk-sysext.sh install     # then: sudo punktfunk-sysext update | status | remove
+```
+
+Full walkthrough (incl. the F43→F44 rebase behavior and migration off layering):
+[`bazzite/README.md`](bazzite/README.md).
+
+## Option B — Gitea RPM registry (per-host, `rpm-ostree` layering)
 
 The host's RPM is published to **unom's self-hosted Gitea RPM registry** (CI builds it on every
 push), mirroring the [Debian/apt](debian/README.md) setup. Add one repo file, install, and track
@@ -60,7 +77,7 @@ rpm-ostree install punktfunk && systemctl reboot
 # updates:  rpm-ostree upgrade && systemctl reboot
 ```
 
-## Option B — COPR (per-host, `rpm-ostree install`)
+## Option C — COPR (per-host, `rpm-ostree install`)
 
 1. Create a COPR project, enable **build-from-SCM** pointing at this repo, spec path
    `packaging/rpm/punktfunk.spec` (see `copr/README.md`). Under *External Repositories* add
@@ -78,7 +95,7 @@ rpm-ostree install punktfunk && systemctl reboot
    systemctl reboot
    ```
 
-## Option C — bootc (image-based, atomic)
+## Option D — bootc (image-based, atomic)
 
 Layer punktfunk into a Bazzite image once, then rebase any number of hosts onto it — no
 per-host drift. See `bootc/Containerfile`:
@@ -89,7 +106,7 @@ podman push  ghcr.io/<you>/bazzite-punktfunk
 sudo bootc switch ghcr.io/<you>/bazzite-punktfunk && systemctl reboot
 ```
 
-## First-run setup (either option)
+## First-run setup (all options)
 
 ```sh
 ujust add-user-to-input-group           # virtual gamepads need /dev/uinput (then re-login).
@@ -109,8 +126,8 @@ web console at `https://<host-ip>:47992` or directly.
 
 > ⚠️ **COPR caveat:** COPR's mock chroot has no `bun`, so a COPR build produces only
 > `punktfunk` + `punktfunk-client` — **not** `punktfunk-web`. For the console on a COPR/bootc host,
-> install from the **Gitea RPM registry** (Option A — it carries `punktfunk-web`), which is also why
-> `bootc/Containerfile` installs from there rather than COPR.
+> install from the **Gitea RPM registry** (Option B — it carries `punktfunk-web`; the sysext image
+> includes it too), which is also why `bootc/Containerfile` installs from there rather than COPR.
 
 ## Why not Flatpak (for the HOST)?
 

packaging/arch/PKGBUILD

@@ -10,20 +10,28 @@
 #   - In-tree / CI:       PF_SRCDIR=$(git rev-parse --show-toplevel) makepkg --holdver
 #                         (builds the working tree instead of the tagged source — see build()).
 #
-# IMPORTANT: host encode is NVENC-only (crates/punktfunk-host/src/encode/linux.rs) — functional on
-# NVIDIA hosts; an AMD Deck-as-HOST needs a VAAPI backend first. The CLIENT decodes via VAAPI
-# (AMD/Intel, incl. the Deck) with a software fallback, so it works everywhere. See README.md.
+# Host encode: NVENC on NVIDIA (nvidia-utils), VAAPI on AMD/Intel (mesa) — PUNKTFUNK_ENCODER=auto
+# picks per GPU. The CLIENT decodes via VAAPI (AMD/Intel, incl. the Deck) with a software
+# fallback, so it works everywhere. See README.md.
 pkgbase=punktfunk
 # punktfunk-web (the browser console) is OPT-IN: building it needs `bun` (AUR-only as bun-bin on
 # stock Arch/SteamOS), so a default makepkg builds only host+client with no JS tooling — mirroring
 # the RPM spec's `%bcond_with web` (off by default). Set PF_WITH_WEB=1 to also build punktfunk-web
 # (appended to pkgname + bun to makedepends below).
 pkgname=('punktfunk-host' 'punktfunk-client')
-pkgver=0.2.0
-pkgrel=1
+# CI (.gitea/workflows/arch.yml) drives the version: stable tags -> X.Y.Z-1, main pushes ->
+# X.Y.Z-0.<run#> in the separate punktfunk-canary repo (mirrors the RPM's 0.ciN release; pkgrel
+# allows only digits+dots, so the run number carries the monotonic ordering).
+pkgver="${PF_PKGVER:-0.7.0}"
+pkgrel="${PF_PKGREL:-1}"
 arch=('x86_64')
 url="https://git.unom.io/unom/punktfunk"
 license=('MIT OR Apache-2.0')
+# !lto: makepkg's `lto` option injects -flto=auto into CFLAGS; aws-lc-sys (rustls' crypto)
+# compiles its C with those flags and GCC LTO bitcode objects are unreadable by rust's lld
+# linker -> "undefined symbol: aws_lc_*" at link (reproduced 2026-07-04, Arch + rust 1.90).
+# !debug: skip the -debug split package (debuginfo bloat, not shipped).
+options=('!lto' '!debug')
 
 # All build deps for both crates (Arch runtime packages ship their own headers, so these cover
 # build + link). aws-lc/ring need clang+cmake; nasm is for asm.
@@ -36,10 +44,16 @@ if [ "${PF_WITH_WEB:-0}" = 1 ]; then
   makedepends+=('bun')   # `bun-bin` from the AUR if bun isn't in your configured repos
 fi
 
-# AUR source (a tagged release). For an in-tree CI build, set PF_SRCDIR to the repo root and
-# build() uses it instead; see the README.
-source=("git+https://git.unom.io/unom/punktfunk.git#tag=v${pkgver}")
-sha256sums=('SKIP')
+# AUR source (a tagged release). For an in-tree CI build, set PF_SRCDIR to the repo root —
+# build() uses it instead AND the fetch is skipped entirely (a canary pkgver has no tag to
+# clone, and CI already has the checkout).
+if [ -z "${PF_SRCDIR:-}" ]; then
+  source=("git+https://git.unom.io/unom/punktfunk.git#tag=v${pkgver}")
+  sha256sums=('SKIP')
+else
+  source=()
+  sha256sums=()
+fi
 
 _repo() { printf '%s' "${PF_SRCDIR:-$srcdir/punktfunk}"; }
 

packaging/arch/README.md

@@ -23,7 +23,45 @@ default `makepkg` builds only host+client with no JS tooling — mirroring the R
 > Arch + NVIDIA **and** AMD/Intel (incl. the Steam Deck — see the on-device path above). The client
 > decodes via VAAPI on AMD/Intel with a software fallback.
 
-## Arch Linux (mutable)
+## Install from the binary repo (recommended)
+
+CI (`.gitea/workflows/arch.yml`) builds this PKGBUILD in an `archlinux:base-devel` container on
+every push and publishes the packages to the **Gitea Arch package registry** — a plain pacman
+repo, so an Arch box installs and updates punktfunk with `pacman -Syu` like everything else.
+Two repos mirror the deb/rpm channels: `punktfunk` (release tags) and `punktfunk-canary`
+(rolling main-branch builds, versioned `X.Y.Z-0.<run#>` so a later release always outranks
+them). Enable exactly one.
+
+The registry **signs the repo database and every package**, so first import its key into
+pacman's keyring (a one-time step — after this, packages install signature-verified):
+
+```sh
+# 1. Trust the registry signing key.
+curl -fsS https://git.unom.io/api/packages/unom/arch/repository.key \
+  | sudo pacman-key --add -
+sudo pacman-key --lsign-key E0CA04465C99C936E0B0C6510A317015A34DDD69
+
+# 2. Add the repo (pick ONE channel — punktfunk for releases, punktfunk-canary for main builds).
+sudo tee -a /etc/pacman.conf >/dev/null <<'EOF'
+
+[punktfunk]
+Server = https://git.unom.io/api/packages/unom/arch/$repo/$arch
+EOF
+
+# 3. Sync + install.
+sudo pacman -Sy punktfunk-host        # gaming rig
+sudo pacman -Sy punktfunk-client      # couch/Deck side
+sudo pacman -Sy punktfunk-web         # optional browser management console
+```
+
+(No `SigLevel` line needed — pacman's default `Required DatabaseOptional` verifies the signed
+packages against the key you just trusted. Arch is rolling, so the packages are built against
+current Arch sonames — keep the box itself updated too.)
+
+Then the same first-run steps as a source build (printed by the install scriptlet): `input`
+group, `host.env`, `systemctl --user enable --now punktfunk-host` — see the next section.
+
+## Build from source — Arch Linux (mutable)
 
 ```sh
 cd packaging/arch

packaging/bazzite/README.md

@@ -12,34 +12,91 @@ flagged explicitly. For the higher-level packaging rationale ("why not Flatpak",
 > NVENC, from RPM Fusion **nonfree**), `opus`, and `libei`.
 > Source: `packaging/README.md`, `packaging/rpm/punktfunk.spec`.
 
-> ⚠️ **Read this first — the COPR is operator-run, not yet published.**
-> Both install paths below pull the punktfunk RPM from a COPR project named
-> `enricobuehler/punktfunk`. That COPR is a configuration the maintainer has to **create and
-> build** (see `packaging/copr/README.md` — it documents how to set it up, not a live repo URL you
-> can assume exists). If `rpm-ostree install punktfunk` 404s, the COPR hasn't been published yet,
-> and your only path is to **build the RPM yourself** (see the appendix). The guide flags every
-> command that depends on the COPR being live.
+> ⚠️ **COPR note (Path C only).** The legacy layering path's commands reference a COPR project
+> named `enricobuehler/punktfunk` that is operator-run and may not be published (see
+> `packaging/copr/README.md`); layer from the **Gitea RPM registry** instead (`../rpm/README.md`,
+> the repo file `https://git.unom.io/api/packages/unom/rpm/bazzite.repo`) — it's what CI
+> actually publishes to. Paths A (sysext) and B (bootc) don't involve the COPR at all.
 
 ---
 
 ## 1. Choose an install path
 
-There are two supported paths on Bazzite, driven by different files in `packaging/`:
+There are three paths on Bazzite, driven by different files in `packaging/`:
 
 | Path | Driven by | What it does | Best for |
 |---|---|---|---|
-| **A — rpm-ostree layering** | `packaging/copr/README.md` + `packaging/rpm/punktfunk.spec` | Layers the `punktfunk` RPM onto your existing Bazzite deployment with `rpm-ostree install` | One host, quick iteration |
+| **A — systemd-sysext** ✅ recommended | `packaging/bazzite/punktfunk-sysext.sh` + `build-sysext.sh` (published by `.gitea/workflows/rpm.yml`) | Overlays the host onto `/usr` as a system extension — no layering, no reboot, one-command updates | Everyone; the default |
 | **B — bootc / OCI image** | `packaging/bootc/Containerfile` | Bakes punktfunk into a `FROM bazzite-nvidia` image once; you `bootc switch` any number of hosts onto it | Fleets, reproducible appliances, no per-host drift |
+| **C — rpm-ostree layering** (legacy) | `packaging/rpm/` + the Gitea RPM registry | Layers the `punktfunk` RPM onto your deployment with `rpm-ostree install` | Only if you specifically want the RPM database to own the files |
 
-**Trade-off:** Path A is a per-host package layer — simple, but each host accumulates its own
-layered-package state. Path B builds one image (RPM Fusion + the Gitea RPM repo + the host and
-**web console** + udev rule pre-installed) that you push to a registry and rebase hosts onto
-atomically — no per-host `rpm-ostree install` drift, at the cost of running a `podman build`/`push`
-pipeline. Both require the **same first-run setup** (sections 3–6); note Path B installs from the
-**Gitea RPM registry** (which carries `punktfunk-web`), whereas Path A's COPR builds host+client
-only — for the web console on Path A, layer from the Gitea registry instead (`../rpm/README.md`).
+**Why A over C:** the Bazzite docs treat layering as a last resort — every layered package makes
+every OS update slower and can **block upgrades entirely** until removed. A sysext never enters an
+rpm-ostree transaction: it merges/unmerges at runtime, survives OS updates, and updating punktfunk
+is one command with **no reboot** (layering needs one per update). It's the mechanism the Fedora
+Atomic maintainers ship via [fedora-sysexts](https://fedora-sysexts.github.io/). All paths require
+the **same first-run setup** (sections 3–6).
 
-### Path A — rpm-ostree layering from the COPR
+### Path A — systemd-sysext (recommended)
+
+Run on the Bazzite host:
+
+```sh
+# One-time bootstrap; afterwards the tool is on PATH as `punktfunk-sysext` (it ships inside
+# the image). `--channel canary` for rolling main-branch builds instead of releases.
+curl -fsSLO https://git.unom.io/unom/punktfunk/raw/branch/main/packaging/bazzite/punktfunk-sysext.sh
+sudo bash punktfunk-sysext.sh install
+```
+
+This downloads the newest image for your Fedora base (host + tray + **web console**,
+SHA-256-verified from the feed `…/packages/unom/generic/punktfunk-sysext/f<ver>[-canary]/`),
+installs it as `/var/lib/extensions/punktfunk.raw`, merges it, and immediately applies what the
+RPM scriptlets would have (udev reload, sysctl) plus the two `/etc` files a sysext can't carry
+(the gamescope-session drop-in and the tray autostart entry, staged under
+`/usr/share/punktfunk/etc/`). No reboot at any point. Day-2:
+
+```sh
+sudo punktfunk-sysext update    # fetch + merge the newest build (then restart the user service)
+sudo punktfunk-sysext status    # merged?, installed vs latest, channel/feed
+sudo punktfunk-sysext remove    # unmerge + delete; ~/.config/punktfunk is left alone
+```
+
+Details worth knowing:
+
+- The image embeds `ID=fedora` + `VERSION_ID` (matched through Bazzite's `ID_LIKE`), so after a
+  **major Bazzite rebase** (F43 → F44) the old image is **refused** instead of merging
+  soname-broken binaries — `punktfunk-sysext update` then fetches the image built for the new
+  base (feeds exist per Fedora major, from the same CI matrix as the RPM groups).
+- SELinux labels are baked into the image at build time (squashfs pseudo-xattrs computed from
+  the targeted policy) — without them udev couldn't read the gamepad rule under enforcing.
+  Validated live on Bazzite 43.
+- **Migrating from layering (path C):** install the sysext (it shadows the layered copy at
+  once), then `sudo rpm-ostree uninstall punktfunk punktfunk-web && systemctl reboot`.
+
+### Path B — bootc image (`FROM bazzite-nvidia`)
+
+The image is built **off-host** (on any machine with `podman`) from
+`packaging/bootc/Containerfile`, which bases on `ghcr.io/ublue-os/bazzite-nvidia:stable`
+(override with `--build-arg BASE_IMAGE=…`), enables RPM Fusion free + nonfree, adds the Gitea RPM
+repo (`--build-arg PUNKTFUNK_RPM_GROUP=…`, default `bazzite`), and installs the host **and the web
+console** (`punktfunk punktfunk-web`). It uses the Gitea registry rather than the COPR specifically
+because the registry carries `punktfunk-web` (COPR's mock chroot can't build it — no `bun`).
+
+```sh
+# Build + push (run from the repo root, on your builder machine):
+podman build -t ghcr.io/<you>/bazzite-punktfunk -f packaging/bootc/Containerfile .
+podman push  ghcr.io/<you>/bazzite-punktfunk
+
+# On each target Bazzite host:
+sudo bootc switch ghcr.io/<you>/bazzite-punktfunk && systemctl reboot
+```
+
+> ⚠️ The image installs from the **Gitea RPM registry** (group `bazzite`), so **Path B depends on
+> that registry being populated** — CI (`.gitea/workflows/rpm.yml`) publishes `punktfunk` +
+> `punktfunk-web` on every push to `main`. Packages are unsigned with GPG-signed metadata
+> (`repo_gpgcheck=1`), matching `packaging/rpm/README.md`.
+
+### Path C — rpm-ostree layering (legacy)
 
 Run on the Bazzite host. (Commands verbatim from `packaging/README.md`.)
 
@@ -62,7 +119,7 @@ systemctl reboot
 > The **reboot is mandatory** — `rpm-ostree install` stages a new deployment that only takes
 > effect on the next boot. This is normal atomic-distro behavior, not a punktfunk quirk.
 
-#### Updating a Path-A host — `rpm-ostree upgrade` is NOT enough
+#### Updating a Path-C host — `rpm-ostree upgrade` is NOT enough
 
 > ⚠️ **`rpm-ostree upgrade` will not update punktfunk on its own.** `upgrade` bumps the **base
 > image** and only re-resolves *layered* packages **when the base changes**. A Bazzite base can
@@ -94,29 +151,6 @@ sudo bash packaging/bazzite/update-punktfunk.sh --reboot # stage + reboot now
 > `punktfunk.repo`, canary's `<next-minor>.0-0.ciN` **outranks** the stable `X.Y.Z-1` and the box
 > silently tracks canary. Enable exactly one channel — set `enabled=0` in the other repo file.
 
-### Path B — bootc image (`FROM bazzite-nvidia`)
-
-The image is built **off-host** (on any machine with `podman`) from
-`packaging/bootc/Containerfile`, which bases on `ghcr.io/ublue-os/bazzite-nvidia:stable`
-(override with `--build-arg BASE_IMAGE=…`), enables RPM Fusion free + nonfree, adds the Gitea RPM
-repo (`--build-arg PUNKTFUNK_RPM_GROUP=…`, default `bazzite`), and installs the host **and the web
-console** (`punktfunk punktfunk-web`). It uses the Gitea registry rather than the COPR specifically
-because the registry carries `punktfunk-web` (COPR's mock chroot can't build it — no `bun`).
-
-```sh
-# Build + push (run from the repo root, on your builder machine):
-podman build -t ghcr.io/<you>/bazzite-punktfunk -f packaging/bootc/Containerfile .
-podman push  ghcr.io/<you>/bazzite-punktfunk
-
-# On each target Bazzite host:
-sudo bootc switch ghcr.io/<you>/bazzite-punktfunk && systemctl reboot
-```
-
-> ⚠️ The image installs from the **Gitea RPM registry** (group `bazzite`), so **Path B depends on
-> that registry being populated** — CI (`.gitea/workflows/rpm.yml`) publishes `punktfunk` +
-> `punktfunk-web` on every push to `main`. Packages are unsigned with GPG-signed metadata
-> (`repo_gpgcheck=1`), matching `packaging/rpm/README.md`.
-
 ---
 
 ## 2. Prerequisites — what Bazzite gives you vs. what you must still do

packaging/bazzite/build-sysext.sh

@@ -0,0 +1,115 @@
+#!/usr/bin/env bash
+# Build the punktfunk systemd-sysext image for Bazzite / Fedora Atomic from the built RPMs —
+# the no-layering install path (rpm-ostree layering slows every update and can block upgrades;
+# a sysext never enters an rpm-ostree transaction). The .raw overlays /usr read-only from
+# /var/lib/extensions/, survives OS updates, and is toggled/updated without a reboot.
+#
+# Counterpart to ../arch/build-sysext.sh (which wraps a pacman package for SteamOS). This one
+# wraps the Fedora RPMs (punktfunk + punktfunk-web) and additionally:
+#   * relocates the RPMs' /etc payload to /usr/share/punktfunk/etc/ (a sysext carries ONLY /usr;
+#     punktfunk-sysext(8) copies these into the real /etc on install),
+#   * bakes SELinux labels in as squashfs pseudo-xattrs, computed with matchpathcon from the
+#     build container's targeted policy. Without them every file is unlabeled_t at runtime:
+#     fine for the user session + systemd --user units (unconfined), but system daemons are
+#     DENIED — udev couldn't read 60-punktfunk.rules and systemd-sysctl couldn't read the
+#     sysctl drop-in (validated live on Bazzite 43, SELinux enforcing, 2026-07-04),
+#   * pins compatibility via ID=fedora + VERSION_ID: merges on Bazzite/Silverblue/Aurora of the
+#     SAME Fedora major (ID_LIKE matching, systemd >= 256) and is REFUSED after a major rebase
+#     instead of running soname-broken binaries (`punktfunk-sysext update` then re-resolves),
+#   * embeds the punktfunk-sysext helper so an installed box can update itself.
+#
+# Build in the matching Fedora container (ci/fedora*-rpm.Dockerfile) — matchpathcon needs the
+# Fedora targeted policy (libselinux-utils + selinux-policy-targeted), and the RPMs are
+# soname-coupled to their base anyway. Needs: rpm2cpio, cpio, mksquashfs (>= 4.6), matchpathcon.
+#
+# Usage:
+#   bash build-sysext.sh --version-id 43 --out dist/punktfunk-0.7.1-1-x86-64.raw \
+#        dist/punktfunk-0.7.1-1.fc43.x86_64.rpm dist/punktfunk-web-0.7.1-1.fc43.noarch.rpm
+#
+# The installed image MUST be named punktfunk.raw (the embedded extension-release marker is
+# extension-release.punktfunk; systemd-sysext requires marker == image name) — the feed carries
+# versioned filenames and punktfunk-sysext installs to the fixed name.
+set -euo pipefail
+
+VERSION_ID="" OUT="" RPMS=()
+while [ $# -gt 0 ]; do
+  case "$1" in
+    --version-id) VERSION_ID="${2:?}"; shift 2 ;;
+    --out)        OUT="${2:?}"; shift 2 ;;
+    *)            RPMS+=("$1"); shift ;;
+  esac
+done
+[ -n "$VERSION_ID" ] || { echo "missing --version-id <fedora major, e.g. 43>" >&2; exit 1; }
+[ -n "$OUT" ] || { echo "missing --out <image.raw>" >&2; exit 1; }
+[ "${#RPMS[@]}" -gt 0 ] || { echo "no RPMs given" >&2; exit 1; }
+for tool in rpm2cpio cpio mksquashfs matchpathcon; do
+  command -v "$tool" >/dev/null || { echo "missing tool: $tool" >&2; exit 1; }
+done
+
+HERE="$(cd "$(dirname "$0")" && pwd)"
+STAGE="$(mktemp -d)"
+trap 'rm -rf "$STAGE"' EXIT
+
+# SYSEXT_VERSION_ID from the punktfunk RPM (V-R without the dist tag): what
+# `punktfunk-sysext status` reports as the installed version.
+PF_VR=""
+SEEN_NAMES=" "
+for rpm in "${RPMS[@]}"; do
+  [ -f "$rpm" ] || { echo "no such RPM: $rpm" >&2; exit 1; }
+  name="$(rpm -qp --qf '%{NAME}' "$rpm" 2>/dev/null)"
+  # Two RPMs of the same NAME (e.g. a stale noarch next to the current x86_64 from a sloppy
+  # download glob) silently shadow each other's files — refuse instead of building a chimera.
+  case "$SEEN_NAMES" in *" $name "*) echo "duplicate RPM name '$name' in inputs — pass exactly one RPM per package" >&2; exit 1 ;; esac
+  SEEN_NAMES="$SEEN_NAMES$name "
+  if [ "$name" = punktfunk ]; then
+    PF_VR="$(rpm -qp --qf '%{VERSION}-%{RELEASE}' "$rpm" 2>/dev/null)"
+    PF_VR="${PF_VR%.fc*}"
+  fi
+  rpm2cpio "$rpm" | ( cd "$STAGE" && cpio -idmu --quiet )
+done
+[ -n "$PF_VR" ] || { echo "the punktfunk (host) RPM must be among the inputs" >&2; exit 1; }
+
+# A sysext carries only /usr. Relocate the RPMs' /etc payload (gamescope-session drop-in, tray
+# autostart entry) under /usr/share/punktfunk/etc/ — punktfunk-sysext copies it into /etc.
+if [ -d "$STAGE/etc" ]; then
+  mkdir -p "$STAGE/usr/share/punktfunk/etc"
+  cp -a "$STAGE/etc/." "$STAGE/usr/share/punktfunk/etc/"
+  rm -rf "${STAGE:?}/etc"
+fi
+rm -rf "${STAGE:?}/var"   # rpm ghosts etc. — nothing outside /usr may remain
+
+# Self-update: the helper rides inside the image.
+install -Dm0755 "$HERE/punktfunk-sysext.sh" "$STAGE/usr/bin/punktfunk-sysext"
+
+# Compatibility marker. ID=fedora matches Bazzite & friends through os-release ID_LIKE;
+# VERSION_ID makes a major-rebased host refuse the old ABI instead of merging it.
+install -d "$STAGE/usr/lib/extension-release.d"
+cat > "$STAGE/usr/lib/extension-release.d/extension-release.punktfunk" <<EOF
+ID=fedora
+VERSION_ID=$VERSION_ID
+ARCHITECTURE=x86-64
+SYSEXT_ID=punktfunk
+SYSEXT_VERSION_ID=$PF_VR
+EXTENSION_RELOAD_MANAGER=1
+EOF
+
+# SELinux labels as pseudo-xattrs (see header). matchpathcon resolves each target path against
+# the targeted policy's file_contexts; <<none>> means "no specific entry" — skip those (the
+# handful of matches all resolve to real contexts for our payload).
+PSEUDO="$STAGE.pseudo"
+( cd "$STAGE" && find . -mindepth 1 \( -type f -o -type d \) -printf '/%P\n' ) | sort \
+  | while IFS= read -r path; do
+      ctx="$(matchpathcon -n "$path" 2>/dev/null || true)"
+      case "$ctx" in ''|'<<none>>') continue ;; esac
+      printf '%s x security.selinux=%s\n' "$path" "$ctx"
+    done > "$PSEUDO"
+[ -s "$PSEUDO" ] || { echo "matchpathcon produced no labels — refusing to build an unlabeled image" >&2; exit 1; }
+
+rm -f "$OUT"; mkdir -p "$(dirname "$OUT")"
+# -xattrs-exclude drops any security.selinux the staging fs already had (would collide with the
+# pseudo defs when building on an SELinux host); -all-root because cpio extracted as the CI uid.
+mksquashfs "$STAGE" "$OUT" -all-root -noappend -quiet \
+  -xattrs-exclude '^security.selinux' -pf "$PSEUDO"
+rm -f "$PSEUDO"
+echo "built $OUT (punktfunk $PF_VR, fedora $VERSION_ID, $(du -h "$OUT" | cut -f1))"
+echo "  install on the box:  punktfunk-sysext install   (or --from-file $OUT)"

packaging/bazzite/publish-sysext-feed.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+# Publish a punktfunk sysext image into its feed on the Gitea generic package registry —
+# called by .gitea/workflows/rpm.yml after the RPM publish. A feed is one fixed URL
+# (…/punktfunk-sysext/<feed>/) holding versioned .raw files plus a SHA256SUMS manifest;
+# punktfunk-sysext(8) on the boxes reads SHA256SUMS to find + verify the newest image
+# (the layout is also exactly what systemd-sysupdate's url-file source expects, so a
+# .transfer feed can be added later without re-publishing anything).
+#
+# Usage: TOKEN=… [KEEP=6] bash publish-sysext-feed.sh <feed> <image.raw>
+#   <feed>   e.g. f43, f43-canary, f44 (Fedora major x channel)
+#   KEEP     newest images to keep in the feed; 0/unset-for-stable = keep all
+# Env: REGISTRY (git.unom.io), OWNER (unom), TOKEN (write:package PAT), CURL_USER (login name)
+set -euo pipefail
+
+FEED="${1:?usage: publish-sysext-feed.sh <feed> <image.raw>}"
+RAW="${2:?usage: publish-sysext-feed.sh <feed> <image.raw>}"
+[ -f "$RAW" ] || { echo "no such image: $RAW" >&2; exit 1; }
+REGISTRY="${REGISTRY:-git.unom.io}"
+OWNER="${OWNER:-unom}"
+KEEP="${KEEP:-0}"
+AUTH=(--user "${CURL_USER:-enricobuehler}:${TOKEN:?TOKEN (write:package PAT) required}")
+BASE="https://$REGISTRY/api/packages/$OWNER/generic/punktfunk-sysext/$FEED"
+
+FNAME="$(basename "$RAW")"
+SHA="$(sha256sum "$RAW" | cut -d' ' -f1)"
+
+# Merge into the existing manifest: drop any prior line for this filename, append ours.
+SUMS="$(mktemp)"; trap 'rm -f "$SUMS"' EXIT
+curl -fsS "${AUTH[@]}" "$BASE/SHA256SUMS" 2>/dev/null | grep -v " $FNAME\$" > "$SUMS" || true
+printf '%s  %s\n' "$SHA" "$FNAME" >> "$SUMS"
+
+# Prune: keep only the newest $KEEP images (by version sort) in manifest + registry.
+PRUNE=()
+if [ "$KEEP" -gt 0 ]; then
+  mapfile -t PRUNE < <(awk '{print $2}' "$SUMS" | sort -V | head -n -"$KEEP")
+  for f in "${PRUNE[@]:-}"; do
+    [ -n "$f" ] && sed -i "\| $f\$|d" "$SUMS"
+  done
+fi
+
+# Upload order keeps consumers consistent: image first, then the manifest referencing it,
+# then prune deletions (already absent from the manifest). Delete-before-put makes workflow
+# re-runs idempotent (the registry 409s on duplicate filenames; first-publish 404s are fine).
+curl -fsS -o /dev/null "${AUTH[@]}" -X DELETE "$BASE/$FNAME" || true
+curl -fsS -o /dev/null "${AUTH[@]}" --upload-file "$RAW" "$BASE/$FNAME"
+curl -fsS -o /dev/null "${AUTH[@]}" -X DELETE "$BASE/SHA256SUMS" || true
+curl -fsS -o /dev/null "${AUTH[@]}" --upload-file "$SUMS" "$BASE/SHA256SUMS"
+for f in "${PRUNE[@]:-}"; do
+  [ -n "$f" ] && { echo "pruning $f"; curl -fsS -o /dev/null "${AUTH[@]}" -X DELETE "$BASE/$f" || true; }
+done
+echo "published $FNAME -> $BASE ($(wc -l <"$SUMS") image(s) in the feed)"

packaging/bazzite/punktfunk-sysext.sh

@@ -0,0 +1,204 @@
+#!/usr/bin/env bash
+# punktfunk-sysext — install/update the punktfunk host on Bazzite / Fedora Atomic as a
+# systemd-sysext, the no-layering path (rpm-ostree layering is a last resort per the Bazzite
+# docs: it slows every update and can block upgrades; a sysext never enters an rpm-ostree
+# transaction, needs no reboot, and is trivially removable).
+#
+# The image overlays /usr from /var/lib/extensions/punktfunk.raw with the host, tray and web
+# console + their udev/sysctl/systemd-user payload; the RPMs' two /etc files (gamescope
+# session drop-in, tray autostart) ride inside at /usr/share/punktfunk/etc/ and are copied
+# into the real /etc here (a sysext can only carry /usr).
+#
+# Bootstrap (the script also ships inside the image as /usr/bin/punktfunk-sysext):
+#   curl -fsSLO https://git.unom.io/unom/punktfunk/raw/branch/main/packaging/bazzite/punktfunk-sysext.sh
+#   sudo bash punktfunk-sysext.sh install            # or: install --channel canary
+# Thereafter:
+#   sudo punktfunk-sysext update | status | remove
+#
+# Feed: the Gitea generic package registry, one feed per Fedora major x channel
+# (…/punktfunk-sysext/f43/, f43-canary, f44, …), each a SHA256SUMS + versioned .raw files —
+# published by .gitea/workflows/rpm.yml from the same RPMs the (legacy) layering path uses.
+# The image pins ID=fedora + VERSION_ID, so after a major OS rebase the old image is refused
+# (not merged broken) and `punktfunk-sysext update` re-resolves against the new release.
+set -euo pipefail
+
+REGISTRY="${PUNKTFUNK_SYSEXT_REGISTRY:-https://git.unom.io/api/packages/unom/generic/punktfunk-sysext}"
+CONF=/etc/punktfunk-sysext.conf
+EXT_DIR=/var/lib/extensions
+IMG="$EXT_DIR/punktfunk.raw"
+SIDECAR="$EXT_DIR/.punktfunk.version"
+MARKER=/usr/lib/extension-release.d/extension-release.punktfunk
+ETC_SRC=/usr/share/punktfunk/etc
+
+usage() {
+  sed -n 's/^#\( \|$\)//p' "$0" | sed -n '1,20p'
+  echo "usage: punktfunk-sysext install [--channel stable|canary] [--from-file X.raw]"
+  echo "       punktfunk-sysext update [--from-file X.raw] | status | remove"
+  exit "${1:-0}"
+}
+need_root() { [ "$(id -u)" = 0 ] || { echo "run as root (sudo)" >&2; exit 1; }; }
+
+os_version_id() { . /etc/os-release; echo "${VERSION_ID%%.*}"; }
+channel() { # shellcheck disable=SC1090
+  [ -f "$CONF" ] && . "$CONF"; echo "${CHANNEL:-stable}"; }
+feed_url() {
+  local suffix=""
+  [ "$(channel)" = canary ] && suffix="-canary"
+  echo "$REGISTRY/f$(os_version_id)$suffix"
+}
+
+# latest -> "VERSION FILENAME SHA256" from the feed's SHA256SUMS (highest by version sort).
+latest() {
+  local feed; feed="$(feed_url)"
+  curl -fsSL "$feed/SHA256SUMS" \
+    | awk '$2 ~ /^punktfunk-.*-x86-64\.raw$/ { v=$2; sub(/^punktfunk-/,"",v); sub(/-x86-64\.raw$/,"",v); print v, $2, $1 }' \
+    | sort -V | tail -n1
+}
+
+installed_version() {
+  if [ -f "$MARKER" ]; then
+    sed -n 's/^SYSEXT_VERSION_ID=//p' "$MARKER"
+  elif [ -f "$SIDECAR" ]; then
+    cat "$SIDECAR"
+  fi
+}
+merged() { [ -f "$MARKER" ]; }
+
+post_merge() {
+  if ! merged; then
+    echo "!! image installed but NOT merged — 'systemd-sysext status' / 'journalctl -u systemd-sysext'" >&2
+    echo "!! (an OS release the image doesn't match? 'punktfunk-sysext update' fetches the right one)" >&2
+    return 1
+  fi
+  # What the RPM scriptlets would have done: pick up the uinput/uhid rule + the UDP buffer
+  # sysctl now, no reboot (both also auto-apply at boot once merged — the files live in /usr/lib).
+  udevadm control --reload 2>/dev/null || :
+  udevadm trigger --subsystem-match=misc 2>/dev/null || :
+  for f in /usr/lib/sysctl.d/99-punktfunk-net.conf /usr/lib/sysctl.d/99-punktfunk-client-net.conf; do
+    [ -f "$f" ] && sysctl -q -p "$f" 2>/dev/null || :
+  done
+  # The /etc payload a sysext can't carry. The gamescope-session drop-in is %config(noreplace):
+  # only seed it, never clobber a local edit. The tray autostart entry is not user config.
+  if [ -f "$ETC_SRC/gamescope-session-plus/sessions.d/steam" ] \
+     && [ ! -e /etc/gamescope-session-plus/sessions.d/steam ]; then
+    install -Dm0644 "$ETC_SRC/gamescope-session-plus/sessions.d/steam" \
+      /etc/gamescope-session-plus/sessions.d/steam
+  fi
+  if [ -f "$ETC_SRC/xdg/autostart/io.unom.Punktfunk.Tray.desktop" ]; then
+    install -Dm0644 "$ETC_SRC/xdg/autostart/io.unom.Punktfunk.Tray.desktop" \
+      /etc/xdg/autostart/io.unom.Punktfunk.Tray.desktop
+  fi
+}
+
+# do_install VERSION FILENAME SHA256 | do_install --from-file X.raw
+do_install() {
+  need_root
+  mkdir -p "$EXT_DIR"
+  local tmp="$EXT_DIR/.punktfunk.raw.new" ver
+  if [ "$1" = --from-file ]; then
+    ver="(local: $(basename "$2"))"
+    cp -f "$2" "$tmp"
+  else
+    ver="$1"
+    echo "downloading punktfunk $ver ($(channel), fedora $(os_version_id))…"
+    curl -fL --progress-bar -o "$tmp" "$(feed_url)/$2"
+    echo "$3  $tmp" | sha256sum -c --quiet
+  fi
+  mv -f "$tmp" "$IMG"          # marker inside is extension-release.punktfunk — name must match
+  echo "$ver" > "$SIDECAR"
+  systemctl enable --now systemd-sysext.service >/dev/null 2>&1 || :
+  systemd-sysext refresh
+  post_merge
+  echo "punktfunk $ver merged into /usr."
+}
+
+layering_hint() {
+  if command -v rpm-ostree >/dev/null 2>&1 \
+     && rpm-ostree status 2>/dev/null | grep -q 'LayeredPackages:.*punktfunk'; then
+    cat >&2 <<'EOF'
+!! punktfunk is ALSO layered via rpm-ostree. The sysext now shadows it, but remove the
+!! layer so it stops slowing/blocking OS updates (the reason this sysext exists):
+!!     sudo rpm-ostree uninstall punktfunk punktfunk-web && systemctl reboot
+EOF
+  fi
+}
+
+cmd_install() {
+  need_root
+  local from_file=""
+  while [ $# -gt 0 ]; do
+    case "$1" in
+      --channel)   printf 'CHANNEL=%s\n' "${2:?}" > "$CONF"; shift 2 ;;
+      --from-file) from_file="${2:?}"; shift 2 ;;
+      *) usage 1 ;;
+    esac
+  done
+  if [ -n "$from_file" ]; then
+    do_install --from-file "$from_file"
+  else
+    local l; l="$(latest)"
+    [ -n "$l" ] || { echo "no image in the feed $(feed_url)" >&2; exit 1; }
+    # shellcheck disable=SC2086
+    do_install $l
+  fi
+  layering_hint
+  cat <<'EOF'
+
+First-run (once):
+  ujust add-user-to-input-group        # virtual gamepads; then log out + back in
+  mkdir -p ~/.config/punktfunk
+  cp /usr/share/punktfunk/host.env.bazzite ~/.config/punktfunk/host.env
+  systemctl --user daemon-reload && systemctl --user enable --now punktfunk-host
+Updates:  sudo punktfunk-sysext update
+EOF
+}
+
+cmd_update() {
+  need_root
+  if [ "${1:-}" = --from-file ]; then do_install --from-file "${2:?}"; return; fi
+  local cur l ver
+  cur="$(installed_version)"
+  l="$(latest)"
+  [ -n "$l" ] || { echo "no image in the feed $(feed_url)" >&2; exit 1; }
+  ver="${l%% *}"
+  if [ "$ver" = "$cur" ] && merged; then
+    echo "already on $cur (channel $(channel)) — nothing to do."
+    return
+  fi
+  echo "updating: ${cur:-<none>} -> $ver"
+  # shellcheck disable=SC2086
+  do_install $l
+  echo "restart the host to pick up the new binary:  systemctl --user restart punktfunk-host"
+}
+
+cmd_status() {
+  echo "channel:    $(channel)"
+  echo "feed:       $(feed_url)"
+  echo "image:      $([ -f "$IMG" ] && du -h "$IMG" | cut -f1 || echo '(not installed)')"
+  echo "merged:     $(merged && echo yes || echo no)"
+  echo "installed:  $(installed_version || true)"
+  echo "latest:     $(latest 2>/dev/null | cut -d' ' -f1 || true)"
+}
+
+cmd_remove() {
+  need_root
+  # /etc cleanup needs the /usr payload for the unmodified-compare — do it BEFORE unmerging.
+  if merged; then
+    if cmp -s "$ETC_SRC/gamescope-session-plus/sessions.d/steam" \
+              /etc/gamescope-session-plus/sessions.d/steam 2>/dev/null; then
+      rm -f /etc/gamescope-session-plus/sessions.d/steam
+    fi
+  fi
+  rm -f /etc/xdg/autostart/io.unom.Punktfunk.Tray.desktop
+  rm -f "$IMG" "$SIDECAR" "$CONF"
+  systemd-sysext refresh 2>/dev/null || :
+  echo "punktfunk sysext removed (user config in ~/.config/punktfunk is untouched)."
+}
+
+case "${1:-}" in
+  install) shift; cmd_install "$@" ;;
+  update)  shift; cmd_update "$@" ;;
+  status)  shift; cmd_status ;;
+  remove)  shift; cmd_remove ;;
+  *) usage ;;
+esac

packaging/bazzite/update-punktfunk.sh

@@ -23,6 +23,14 @@ if [[ $EUID -ne 0 ]]; then
   exit 1
 fi
 
+# The sysext path (packaging/bazzite/punktfunk-sysext.sh) supersedes layering entirely — if the
+# box runs the sysext, it shadows any layered copy and THIS script won't change what executes.
+if [[ -f /var/lib/extensions/punktfunk.raw ]]; then
+  echo "NOTE: the punktfunk sysext is installed — update with 'punktfunk-sysext update' instead." >&2
+  echo "      (a layered punktfunk is shadowed by the sysext; consider removing the layer:" >&2
+  echo "       rpm-ostree uninstall punktfunk punktfunk-web)" >&2
+fi
+
 # Which punktfunk packages are actually layered right now (host, web, or both).
 mapfile -t layered < <(rpm-ostree status --json 2>/dev/null \
   | grep -oE '"punktfunk(-web)?"' | tr -d '"' | sort -u)

web/messages/de.json

@@ -47,6 +47,36 @@
 	"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_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_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": "Konfliktbehandlung, Identität und Layout werden gespeichert, aber noch nicht angewendet — sie folgen in späteren Versionen.",
+	"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",
 	"clients_title": "Gekoppelte Geräte",
 	"clients_empty": "Noch keine gekoppelten Geräte.",
 	"clients_name": "Name",

web/messages/en.json

@@ -47,6 +47,36 @@
 	"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_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_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": "Conflict handling, identity, and layout are stored but not enforced yet — they arrive in later releases.",
+	"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",
 	"clients_title": "Paired clients",
 	"clients_empty": "No paired clients yet.",
 	"clients_name": "Name",

web/src/sections/Host/DisplayCard.tsx

@@ -0,0 +1,362 @@
+import { useQueryClient } from "@tanstack/react-query";
+import { Button } from "@unom/ui/button";
+import { type FC, useEffect, useState } from "react";
+import {
+	getGetDisplayStateQueryKey,
+	getGetDisplaySettingsQueryKey,
+	useGetDisplaySettings,
+	useGetDisplayState,
+	useReleaseDisplay,
+	useSetDisplaySettings,
+} from "@/api/gen/display/display";
+import type { ApiDisplayInfo } from "@/api/gen/model";
+import { ApiError } from "@/api/fetcher";
+import type {
+	DisplayPolicy,
+	EffectivePolicy,
+	KeepAlive,
+	Preset,
+	Topology,
+} from "@/api/gen/model";
+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 { m } from "@/paraglide/messages";
+
+/**
+ * Container: the host's virtual-display management policy (design/display-management.md). Reads the
+ * stored policy + preset expansions, lets the operator pick a preset or set Custom fields, and PUTs
+ * the result — a change applies to the next session. Stage 0 enforces keep-alive + topology; the
+ * other stored options are shown but marked not-yet-enforced.
+ */
+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 a successful save.
+	const [draft, setDraft] = useState<DisplayPolicy | null>(null);
+	useEffect(() => {
+		if (q.data && draft === null) setDraft(q.data.settings);
+	}, [q.data, draft]);
+
+	const onSave = () => {
+		if (!draft) return;
+		save.mutate(
+			{ data: draft },
+			{
+				onSuccess: (res) => {
+					setDraft(res.settings);
+					qc.invalidateQueries({ queryKey: getGetDisplaySettingsQueryKey() });
+				},
+			},
+		);
+	};
+
+	return (
+		<Card>
+			<CardHeader>
+				<CardTitle>{m.host_displays()}</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}
+							onSave={onSave}
+							busy={save.isPending}
+							error={apiErrorMessage(save.error)}
+						/>
+					)}
+				</QueryState>
+				<LiveDisplays />
+			</CardContent>
+		</Card>
+	);
+};
+
+/**
+ * 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-2 border-t pt-4">
+			<div className="flex items-center justify-between gap-4">
+				<h4 className="text-sm font-medium">{m.display_live()}</h4>
+				{kept.length > 0 && (
+					<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>
+			)}
+		</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
+						? ` · ${m.display_expires_in({ sec: Math.ceil(d.expires_in_ms / 1000) })}`
+						: ""}
+				</code>
+			</div>
+			{!active && (
+				<Button size="sm" variant="outline" disabled={busy} onClick={onRelease}>
+					{m.display_release_btn()}
+				</Button>
+			)}
+		</li>
+	);
+};
+
+/** The server's `{ error }` message from a thrown `ApiError` (its `.data` body), for inline display. */
+const apiErrorMessage = (err: unknown): string | undefined => {
+	if (err instanceof ApiError) {
+		const data = err.data as { error?: string } | undefined;
+		return data?.error ?? err.message;
+	}
+	return err ? String(err) : undefined;
+};
+
+/** The `gaming-rig` preset expands to `keep_alive: forever`, which the host rejects until the
+ * display-lifecycle stage — disable it rather than let the Save 400. */
+const DISABLED_PRESETS: ReadonlySet<string> = new Set(["gaming-rig"]);
+
+const PRESET_LABEL: Record<string, () => string> = {
+	custom: m.display_preset_custom,
+	default: m.display_preset_default,
+	"gaming-rig": m.display_preset_gaming_rig,
+	"shared-desktop": m.display_preset_shared_desktop,
+	hotdesk: m.display_preset_hotdesk,
+	workstation: m.display_preset_workstation,
+};
+
+const TOPOLOGY_LABEL: Record<Topology, () => string> = {
+	auto: m.display_topology_auto,
+	extend: m.display_topology_extend,
+	primary: m.display_topology_primary,
+	exclusive: m.display_topology_exclusive,
+};
+
+const fmtKeepAlive = (k: KeepAlive): string => {
+	switch (k.mode) {
+		case "off":
+			return m.display_keep_alive_off();
+		case "duration":
+			return `${k.seconds} ${m.display_keep_alive_seconds()}`;
+		case "forever":
+			return "∞";
+	}
+};
+
+const DisplayForm: FC<{
+	draft: DisplayPolicy;
+	setDraft: (p: DisplayPolicy) => void;
+	presets: { id: string; summary: string; fields: EffectivePolicy }[];
+	onSave: () => void;
+	busy: boolean;
+	error?: string;
+}> = ({ draft, setDraft, presets, onSave, busy, error }) => {
+	const preset: Preset = draft.preset ?? "custom";
+	const isCustom = preset === "custom";
+	const keepAlive: KeepAlive = draft.keep_alive ?? { mode: "duration", seconds: 10 };
+	const topology: Topology = draft.topology ?? "auto";
+
+	// Preview the effective fields: from the selected preset's expansion, or the Custom fields.
+	const effective: EffectivePolicy | undefined = isCustom
+		? {
+				keep_alive: keepAlive,
+				topology,
+				mode_conflict: draft.mode_conflict ?? "separate",
+				identity: draft.identity ?? "per-client",
+				layout: draft.layout ?? { mode: "auto-row", positions: {} },
+				max_displays: draft.max_displays ?? 4,
+			}
+		: presets.find((p) => p.id === preset)?.fields;
+
+	const presetSummary = presets.find((p) => p.id === preset)?.summary;
+
+	const secondsValue = keepAlive.mode === "duration" ? keepAlive.seconds : 300;
+
+	return (
+		<div className="space-y-5">
+			{/* Preset picker */}
+			<div className="space-y-2">
+				<Label>{m.display_preset()}</Label>
+				<div className="flex flex-wrap gap-2">
+					{(["custom", "default", "gaming-rig", "shared-desktop", "hotdesk", "workstation"] as const).map(
+						(id) => (
+							<Button
+								key={id}
+								size="sm"
+								variant={preset === id ? "default" : "outline"}
+								disabled={busy || DISABLED_PRESETS.has(id)}
+								onClick={() => setDraft({ ...draft, preset: id as Preset })}
+							>
+								{(PRESET_LABEL[id] ?? (() => id))()}
+							</Button>
+						),
+					)}
+				</div>
+				{presetSummary && !isCustom && (
+					<p className="text-xs text-muted-foreground">{presetSummary}</p>
+				)}
+			</div>
+
+			{/* Custom fields: keep-alive + topology + max displays */}
+			{isCustom && (
+				<div className="space-y-4 rounded-md border p-4">
+					<div className="space-y-2">
+						<Label>{m.display_keep_alive()}</Label>
+						<div className="flex items-center gap-2">
+							<Button
+								size="sm"
+								variant={keepAlive.mode === "off" ? "default" : "outline"}
+								disabled={busy}
+								onClick={() => setDraft({ ...draft, keep_alive: { mode: "off" } })}
+							>
+								{m.display_keep_alive_off()}
+							</Button>
+							<Input
+								type="number"
+								min={0}
+								className="w-24"
+								value={secondsValue}
+								disabled={busy}
+								onChange={(e) =>
+									setDraft({
+										...draft,
+										keep_alive: {
+											mode: "duration",
+											seconds: Math.max(0, Number(e.target.value) || 0),
+										},
+									})
+								}
+							/>
+							<span className="text-sm text-muted-foreground">
+								{m.display_keep_alive_seconds()}
+							</span>
+						</div>
+					</div>
+
+					<div className="space-y-2">
+						<Label>{m.display_topology()}</Label>
+						<div className="flex flex-wrap gap-2">
+							{(["auto", "extend", "primary", "exclusive"] as const).map((t) => (
+								<Button
+									key={t}
+									size="sm"
+									variant={topology === t ? "default" : "outline"}
+									disabled={busy}
+									onClick={() => setDraft({ ...draft, topology: t })}
+								>
+									{TOPOLOGY_LABEL[t]()}
+								</Button>
+							))}
+						</div>
+					</div>
+
+					<div className="space-y-2">
+						<Label htmlFor="disp-max">{m.display_max()}</Label>
+						<Input
+							id="disp-max"
+							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)),
+								})
+							}
+						/>
+					</div>
+				</div>
+			)}
+
+			{/* Effective preview */}
+			{effective && (
+				<div className="flex flex-wrap items-center gap-2">
+					<span className="text-sm text-muted-foreground">{m.display_effective()}:</span>
+					<Badge variant="secondary">{fmtKeepAlive(effective.keep_alive)}</Badge>
+					<Badge variant="secondary">{TOPOLOGY_LABEL[effective.topology]()}</Badge>
+					<Badge variant="outline">{effective.mode_conflict}</Badge>
+					<Badge variant="outline">{effective.identity}</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>
+			)}
+
+			<Button onClick={onSave} disabled={busy}>
+				{m.display_save()}
+			</Button>
+		</div>
+	);
+};

web/src/sections/Host/index.tsx

@@ -1,6 +1,7 @@
 import type { FC } from "react";
 import { useGetHostInfo, useListCompositors } from "@/api/gen/host/host";
 import { useLocale } from "@/lib/i18n";
+import { DisplaySection } from "./DisplayCard";
 import { GpuSection } from "./GpuCard";
 import { HostView } from "./view";
 
@@ -10,6 +11,11 @@ export const SectionHost: FC = () => {
 	const compositors = useListCompositors();
 
 	return (
-		<HostView host={host} compositors={compositors} gpu={<GpuSection />} />
+		<HostView
+			host={host}
+			compositors={compositors}
+			gpu={<GpuSection />}
+			displays={<DisplaySection />}
+		/>
 	);
 };

web/src/sections/Host/view.tsx

@@ -13,7 +13,9 @@ export const HostView: FC<{
 	compositors: Loadable<AvailableCompositor[]>;
 	/** The GPU inventory/selection card (a self-contained container — see `GpuCard.tsx`). */
 	gpu?: ReactNode;
-}> = ({ host, compositors, gpu }) => {
+	/** The virtual-display management card (self-contained container — see `DisplayCard.tsx`). */
+	displays?: ReactNode;
+}> = ({ host, compositors, gpu, displays }) => {
 	const h = host.data;
 	return (
 		<Section maxWidth={false}>
@@ -81,6 +83,8 @@ export const HostView: FC<{
 
 				{gpu}
 
+				{displays}
+
 				<Card>
 					<CardHeader>
 						<CardTitle>{m.host_compositors()}</CardTitle>