feat(clients/windows): port the Vulkan session client to Windows — session-always

The punktfunk-session Vulkan client (clients/linux-session, now clients/session)
builds and runs on Windows; the WinUI shell spawns it for every stream. Verified
live: 10-bit HEVC via Vulkan Video on both AMD (iGPU) and NVIDIA, 5120x1440 at
130 fps / 8 ms end-to-end on the RTX 4090.

- pf-ffvk: Windows bindgen branch (FFMPEG_DIR + PF_FFVK_VULKAN_INCLUDE, no
  pkg-config); provisioning fetches Vulkan-Headers (pinned v1.4.309).
- pf-client-core: builds on Windows — WASAPI audio (audio_wasapi.rs, cfg-swapped
  via #[path], same surface as the PipeWire twin), VAAPI/dmabuf gated inline
  (chain = vulkan -> software), trust reads the WinUI shell's %APPDATA% stores
  (parity tests pin both serialized shapes), Settings gains adapter/hdr_enabled
  (serde-defaulted; Linux stores unaffected).
- pf-presenter: builds on Windows — dmabuf module Linux-gated; SDL keyboard grab
  while captured (Alt+Tab/Win reach the host); pick_device ranks discrete over
  integrated (device 0 was the iGPU on hybrid boxes — the silent footgun) and
  honors PUNKTFUNK_VK_ADAPTER (the Settings GPU pick, exported by the session).
- run loop: block in one SDL wait woken by input AND decoded frames (a per-
  session forwarder pushes a FrameWake user event) instead of a 1 ms poll —
  measured 111%% -> 5%% of a core (NVIDIA), 86%% -> 3.5%% (AMD), stats unchanged.
  The pump's decode-fence wait became once-per-window sampling (no per-frame
  pipeline stall; the stat now shows true backlog).
- pf-console-ui: builds on Windows (skia-safe msvc prebuilts); font lookup falls
  through fontconfig aliases to concrete DirectWrite families (Consolas/Segoe UI)
  — browse/coverflow works, verified against a live host.
- WinUI shell: session-always via new src/spawn.rs (GTK spawn.rs port —
  CREATE_NO_WINDOW, stdout contract, kill handle); the Stream screen is a status
  card (chips + stage lines from the child's stats). The legacy in-process
  D3D11VA path stays behind Settings "Streaming engine" / PUNKTFUNK_BUILTIN_
  STREAM=1 as the A/B baseline until Phase 8 deletes it. SessionParams.video_caps
  makes the HDR toggle real.
- clients/linux-session renamed to clients/session (builds for both OSes).
- CI/MSIX: both workflows build/test both bins with widened path filters; the
  MSIX ships punktfunk-session.exe. ARM64 session builds --no-default-features
  (rust-skia has no aarch64-pc-windows-msvc prebuilts; flip when it does).

A/B on this box (5120x1440 HEVC vs home-worker-5): NVIDIA Vulkan 130 fps / 8 ms
e2e / 1.6 ms decode — clearly better than the built-in path. The AMD iGPU VCN
saturates at ~52 fps where its own D3D11VA does ~70 — Adrenalin Vulkan decode is
slower on APU silicon; discrete RDNA validation gates Phase 8.

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

.gitea/workflows/windows-msix.yml

@@ -33,7 +33,12 @@ on:
     branches: [main]
     paths:
       - 'clients/windows/**'
+      - 'clients/session/**'
       - 'crates/punktfunk-core/**'
+      - 'crates/pf-client-core/**'
+      - 'crates/pf-presenter/**'
+      - 'crates/pf-console-ui/**'
+      - 'crates/pf-ffvk/**'
       - 'Cargo.lock'
       - 'Cargo.toml'
       - '.gitea/workflows/windows-msix.yml'
@@ -57,10 +62,15 @@ jobs:
             target: x86_64-pc-windows-msvc
             ffmpeg: C:\Users\Public\ffmpeg
             td: C:\t
+            session_flags: ''
           - arch: arm64
             target: aarch64-pc-windows-msvc
             ffmpeg: C:\Users\Public\ffmpeg-arm64
             td: C:\t-a64
+            # No skia-binaries prebuilt for aarch64-pc-windows-msvc: the session ships
+            # without the Skia console UI on ARM64 (streaming unaffected) — flip when
+            # rust-skia adds the target.
+            session_flags: '--no-default-features'
     steps:
       - uses: actions/checkout@v4
 
@@ -78,6 +88,8 @@ jobs:
           "CARGO_WORKSPACE_DIR=$env:GITHUB_WORKSPACE" | Out-File -FilePath $env:GITHUB_ENV -Append -Encoding utf8
           "CARGO_TARGET_DIR=${{ matrix.td }}" | Out-File -FilePath $env:GITHUB_ENV -Append -Encoding utf8
           "FFMPEG_DIR=${{ matrix.ffmpeg }}" | Out-File -FilePath $env:GITHUB_ENV -Append -Encoding utf8
+          # pf-ffvk's bindgen needs Vulkan headers (arch-independent; provisioned alongside FFmpeg).
+          "PF_FFVK_VULKAN_INCLUDE=C:\Users\Public\vulkan-headers\include" | Out-File -FilePath $env:GITHUB_ENV -Append -Encoding utf8
           rustup target add ${{ matrix.target }}
           $pf = & "$env:GITHUB_WORKSPACE/scripts/ci/pf-version.ps1"   # single source of truth: base is one minor ahead of the latest stable tag
           $parts = if ($env:GITHUB_REF -like 'refs/tags/v*') {
@@ -92,9 +104,11 @@ jobs:
           "MSIX_VERSION=$v" | Out-File -FilePath $env:GITHUB_ENV -Append -Encoding utf8
           Write-Output "MSIX version $v  arch ${{ matrix.arch }}  target ${{ matrix.target }}"
 
+      # Both client binaries — the shell spawns punktfunk-session.exe (a package sibling)
+      # for every stream. --no-default-features on ARM64 is a no-op for the shell.
       - name: Build (release)
         shell: pwsh
-        run: cargo build --release -p punktfunk-client-windows --target ${{ matrix.target }}
+        run: cargo build --release -p punktfunk-client-windows -p punktfunk-client-session ${{ matrix.session_flags }} --target ${{ matrix.target }}
 
       - name: Pack + sign MSIX
         shell: pwsh