feat(windows): parallel virtual displays — proto v3 ring binding, manager slot map, group topology (W0–W3)

design/windows-parallel-virtual-displays.md (display-management Stage 7 / §6.6): N
simultaneously-live pf-vdisplay monitors, one sealed ring each, every idd-push-security
invariant preserved per-ring.

- proto v3: SharedHeader._pad → target_id — the ring NAMES its monitor, host-stamped
  before the magic; the driver publisher refuses a cross-bound ring via the shared,
  unit-tested frame::check_attach (new DRV_STATUS_BIND_FAIL — the gamepad pad_index
  validation applied to frames, invariant #10); the host's wait_for_attach surfaces the
  refusal loudly and self-checks its own stamp.
- manager: the one-monitor MgrState becomes a slot map keyed by the client's identity
  slot (0 = anonymous/GameStream); per-slot reconnect + dead-WUDFHost preempts,
  slot-scoped begin_idd_setup (a different identity is an admission question, never a
  preempt), ONE device-level watchdog pinger, per-slot /display/state + /display/release.
- group topology: isolate_displays_ccd takes the managed target SET (a sibling slot is
  never deactivated); SavedConfig + the DDC/PnP axes move to the group record (first-in
  captures, last-out restores); desktop layout via CCD source origins from the pure
  layout::arrange (auto-row default, manual pins win), re-applied on create + reconfigure.
- admission: the Windows separate→reject override now sits behind the
  PUNKTFUNK_WIN_SEPARATE=1 validation hatch (the wedge it guarded is structurally gone —
  a second identity gets its own monitor + ring; default flips in W5 after soak);
  max_displays and NVENC session-unit budgets decline an unaffordable display AT
  admission; kick_dwm_compose is process-globally throttled and per-display — cursor
  jump + 35 ms dwell (a sub-tick jump composes nothing; DWM reads dirties from current
  state at the next vsync tick).

On-glass on the RTX box: V1/V2/V4/V5/V6/V9 green — two paired clients on two monitors
streaming ~60 fps each with zero mismatches and zero bind failures, churn-hammer clean
(no 0x80070490), per-ring mode-change recreate leaves the sibling untouched, typed
budget rejection, fault-injected cross-bind refused loudly with the sibling undisturbed.
V7: WUDFHost-kill shared fate is clean; in-process device recovery is a known follow-up
(the retired-never-closed control handles block the adapter cycle — reset-pf-vdisplay.ps1
recovers). DWM composes two IDD monitors concurrently at 60 fps — the plan's
load-bearing unknown, answered yes.

Also carries the client-HDR EDID forwarding that shared this working tree
(Hello::display_hdr → AddRequest luminance tail → the monitor's CTA-861.3 HDR block,
PUNKTFUNK_CLIENT_PEAK_NITS hatch) and the Deck client fixes (40 ms rumble keep-alive
with 1-LSB jitter, HDR self-diagnosing presenter warn, flatpak HDR env).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packaging/flatpak/io.unom.Punktfunk.yml

@@ -84,6 +84,22 @@ finish-args:
   - --share=network
   # --- persistent client identity / pairing store (shared with punktfunk-probe) ---
   - --filesystem=~/.config/punktfunk:create   # client-{cert,key}.pem, known-hosts, settings
+  # --- HDR under gamescope (Steam Deck Game Mode) ---
+  # A flatpak's Vulkan loader can't see the host's gamescope WSI layer, so the SDL3 surface never
+  # offers the HDR10 (ST.2084) colorspace and the presenter silently tone-maps PQ->SDR — the
+  # Game-Mode HDR indicator stays dark (verified on a Deck OLED: the sandbox loader found NO
+  # frog/gamescope layer). The layer ships as the runtime extension
+  # `org.freedesktop.Platform.VulkanLayer.gamescope`, which org.gnome.Platform//50 auto-mounts at
+  # /usr/lib/extensions/vulkan/gamescope once installed (a one-time, per-Deck step; keep it in the
+  # Decky plugin's setup / docs):
+  #     flatpak install --user -y flathub org.freedesktop.Platform.VulkanLayer.gamescope//25.08
+  # These two env vars are all the app itself needs: the first puts the layer's implicit-layer JSON
+  # on the Vulkan loader's search path (the runtime point mounts the files but not onto the path),
+  # the second flips the layer's own `enable_environment` gate. With both, the surface starts
+  # offering HDR10 and the presenter's existing HDR10 swapchain path engages automatically — no
+  # client code change. Harmless off-Deck: the layer no-ops when there's no gamescope socket.
+  - --env=VK_ADD_IMPLICIT_LAYER_PATH=/usr/lib/extensions/vulkan/gamescope/share/vulkan/implicit_layer.d
+  - --env=ENABLE_GAMESCOPE_WSI=1
 
 build-options:
   append-path: /usr/lib/sdk/rust-stable/bin:/usr/lib/sdk/llvm20/bin