fix(host/windows): HDR cursor brightness (203-nit) + probe-before-adopt recovery; windows-client bootstrap doc

- HDR cursor: sRGB→linear decode + scale to HDR graphics white (PUNKTFUNK_HDR_CURSOR_NITS, default
  203 per BT.2408) in the FP16 cursor composite, so it's no longer ~2.5x too dim. SDR path unchanged;
  the masked-color (I-beam) inversion blend left unscaled. Cursor cbuffer widened 16→32 + bound to PS.
  (Validated live: cursor now correct brightness in HDR.)
- Secure-desktop recovery: recreate_dupl now PROBES the rebuilt duplication with a 50ms
  AcquireNextFrame and only adopts it when live (Ok/WAIT_TIMEOUT); a born-lost one (immediate
  ACCESS_LOST) is dropped so the caller repeats the last frame + retries. Plus reassert_isolation()
  re-detaches physical displays on every recovery (re-routing the secure/HDR desktop to the virtual
  output, the delta a fresh reconnect has). NOTE: the born-lost ACCESS_LOST storm in HDR is NOT yet
  resolved by these — still under investigation (animations/secure-UI/cursor-trail in HDR remain).
- docs/windows-client-bootstrap.md: handoff for the native Windows Rust client (windows-rs Reactor +
  WinUI 3 SwapChainPanel, D3D11VA decode, WASAPI audio, SDL3 input; ports crates/punktfunk-client-linux;
  10-bit/HDR present; dev boxes + gotchas).

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

crates/punktfunk-host/src/capture/dxgi.rs

@@ -206,8 +206,21 @@ VOut main(uint vid : SV_VertexID) {
 const CURSOR_PS: &str = r"
 Texture2D tx : register(t0);
 SamplerState sm : register(s0);
+// b0 is shared with the VS: float4 rect, then the HDR cursor params. For SDR white_mul=1 / decode=0
+// so this is a no-op (returns the raw sampled BGRA, blended in the display's native sRGB space). For
+// HDR the cursor is composited onto a LINEAR scRGB FP16 surface where 1.0 = 80 nits, so we sRGB→
+// linear decode (correct alpha blending + no dark edge fringe) and scale to HDR graphics white
+// (~203 nits → white_mul = 203/80) so the cursor isn't ~2.5x too dim vs the HDR desktop.
+cbuffer C : register(b0) { float4 rect; float white_mul; float decode; float2 pad; };
+float3 srgb_to_linear(float3 c) {
+    return c <= 0.04045 ? c / 12.92 : pow((c + 0.055) / 1.055, 2.4);
+}
 float4 main(float4 pos : SV_POSITION, float2 uv : TEXCOORD0) : SV_TARGET {
-    return tx.Sample(sm, uv);
+    float4 s = tx.Sample(sm, uv);
+    float3 rgb = s.rgb;
+    if (decode > 0.5) { rgb = srgb_to_linear(rgb); }
+    rgb *= white_mul;
+    return float4(rgb, s.a);
 }
 ";
 
@@ -267,7 +280,7 @@ impl CursorCompositor {
         device.CreatePixelShader(&psb, None, Some(&mut ps))?;
 
         let cbd = D3D11_BUFFER_DESC {
-            ByteWidth: 16,
+            ByteWidth: 32, // float4 rect + (white_mul, decode, pad, pad) for the HDR cursor PS
             Usage: D3D11_USAGE_DYNAMIC,
             BindFlags: D3D11_BIND_CONSTANT_BUFFER.0 as u32,
             CPUAccessFlags: D3D11_CPU_ACCESS_WRITE.0 as u32,
@@ -375,6 +388,13 @@ impl CursorCompositor {
         cx: i32,
         cy: i32,
         invert: bool,
+        // HDR (decode=true): sRGB→linear decode + scale the cursor to `white_mul` × 80 nits, so a
+        // white cursor hits HDR graphics white (~203 nits) not 80. SDR passes white_mul=1.0,
+        // decode=false → the PS returns the raw sample (blended in the display's native sRGB space).
+        // The inversion (masked-color / I-beam) blend operates on the framebuffer reference, so it is
+        // left unscaled/undecoded even in HDR.
+        white_mul: f32,
+        decode: bool,
     ) {
         let (srv, cw, ch) = match &self.tex {
             Some(t) => t,
@@ -384,13 +404,19 @@ impl CursorCompositor {
         let x1 = ((cx + *cw as i32) as f32 / fw as f32) * 2.0 - 1.0;
         let y0 = 1.0 - (cy as f32 / fh as f32) * 2.0;
         let y1 = 1.0 - ((cy + *ch as i32) as f32 / fh as f32) * 2.0;
-        let rect = [x0, y0, x1, y1];
+        let (mul, dec) = if invert {
+            (1.0_f32, 0.0_f32)
+        } else {
+            (white_mul, if decode { 1.0 } else { 0.0 })
+        };
+        // cbuf layout: [rect.x, rect.y, rect.z, rect.w, white_mul, decode, pad, pad] (32 bytes).
+        let cb = [x0, y0, x1, y1, mul, dec, 0.0, 0.0];
         let mut mapped = D3D11_MAPPED_SUBRESOURCE::default();
         if ctx
             .Map(&self.cbuf, 0, D3D11_MAP_WRITE_DISCARD, 0, Some(&mut mapped))
             .is_ok()
         {
-            std::ptr::copy_nonoverlapping(rect.as_ptr(), mapped.pData as *mut f32, 4);
+            std::ptr::copy_nonoverlapping(cb.as_ptr(), mapped.pData as *mut f32, cb.len());
             ctx.Unmap(&self.cbuf, 0);
         }
         let vp = D3D11_VIEWPORT {
@@ -412,6 +438,7 @@ impl CursorCompositor {
         ctx.VSSetShader(&self.vs, None);
         ctx.PSSetShader(&self.ps, None);
         ctx.VSSetConstantBuffers(0, Some(&[Some(self.cbuf.clone())]));
+        ctx.PSSetConstantBuffers(0, Some(&[Some(self.cbuf.clone())])); // white_mul/decode for the PS
         ctx.PSSetShaderResources(0, Some(&[Some(srv.clone())]));
         ctx.PSSetSamplers(0, Some(&[Some(self.sampler.clone())]));
         ctx.IASetInputLayout(None);
@@ -1110,8 +1137,11 @@ impl DuplCapturer {
         }
     }
 
-    /// Composite the cursor onto the GPU frame texture (zero-copy path).
+    /// Composite the cursor onto the GPU frame texture (zero-copy path). `hdr` = the target is the
-    unsafe fn composite_cursor_gpu(&mut self, gpu: &ID3D11Texture2D) -> Result<()> {
+    /// linear scRGB FP16 surface (HDR path) — the cursor is then sRGB→linear decoded and scaled to
+    /// HDR graphics white (PUNKTFUNK_HDR_CURSOR_NITS, default 203, per BT.2408) so it isn't ~2.5×
+    /// too dim; SDR composites the raw cursor in the display's native sRGB space.
+    unsafe fn composite_cursor_gpu(&mut self, gpu: &ID3D11Texture2D, hdr: bool) -> Result<()> {
         // Diagnostic kill-switch: skip the GPU cursor composite entirely (PUNKTFUNK_NO_CURSOR=1) to
         // isolate its cost on the 3D engine. The per-frame render-target view + draw to the 5K target
         // is the suspect for the high 3D usage under heavy desktop change.
@@ -1151,6 +1181,18 @@ impl DuplCapturer {
             .CreateRenderTargetView(gpu, None, Some(&mut rtv))?;
         let rtv = rtv.context("cursor rtv")?;
         let (cx, cy) = self.cursor_pos;
+        // HDR graphics-white target in nits → scRGB multiplier (scRGB 1.0 = 80 nits). Default 203
+        // (BT.2408); PUNKTFUNK_HDR_CURSOR_NITS overrides without a rebuild. SDR → 1.0, no decode.
+        let white_mul = if hdr {
+            let nits = std::env::var("PUNKTFUNK_HDR_CURSOR_NITS")
+                .ok()
+                .and_then(|s| s.parse::<f32>().ok())
+                .filter(|n| n.is_finite() && *n > 0.0)
+                .unwrap_or(203.0);
+            nits / 80.0
+        } else {
+            1.0
+        };
         self.cursor.as_ref().unwrap().draw(
             &self.context,
             &rtv,
@@ -1159,6 +1201,8 @@ impl DuplCapturer {
             cx,
             cy,
             self.cursor_invert,
+            white_mul,
+            hdr, // decode sRGB→linear only on the HDR (linear FP16) target
         );
         Ok(())
     }
@@ -1183,7 +1227,38 @@ impl DuplCapturer {
             self.gdi_name = n;
         }
         attach_input_desktop();
+        // Re-route the secure (Winlogon) desktop back to the virtual output. The lock/UAC switch can
+        // re-attach a physical monitor so the secure desktop lands there and our virtual output goes
+        // perpetually ACCESS_LOST; re-isolating (as a fresh session's `create` does) is the delta that
+        // makes in-session recovery work like a reconnect. Idempotent/cheap when already isolated.
+        crate::vdisplay::sudovda::reassert_isolation(&self.gdi_name);
         let (dev, ctx, out, dupl) = reopen_duplication(&self.gdi_name)?; // Err → caller repeats + retries
+
+        // PROBE before adopting. During the unsettled Winlogon switch DuplicateOutput SUCCEEDS but the
+        // duplication is "born-lost" — the first AcquireNextFrame immediately returns ACCESS_LOST.
+        // Adopting it (swapping into self + seeding black) is exactly what produced the perpetual
+        // rebuild→born-lost storm (lost=2097) where the secure desktop never appeared. So gate adoption
+        // on a probe: Ok (a frame) or WAIT_TIMEOUT (alive but idle) ⇒ live, adopt; any other error ⇒
+        // born-lost, drop the locals and bail so the caller repeats the last frame and retries on the
+        // 250ms throttle. Once the topology settles (and reassert_isolation has taken), a probe passes
+        // and we adopt a LIVE duplication of the secure desktop.
+        {
+            let mut info = DXGI_OUTDUPL_FRAME_INFO::default();
+            let mut res: Option<IDXGIResource> = None;
+            match dupl.AcquireNextFrame(50, &mut info, &mut res) {
+                Ok(()) => {
+                    let _ = dupl.ReleaseFrame();
+                }
+                Err(e) if e.code() == DXGI_ERROR_WAIT_TIMEOUT => {}
+                Err(e) => {
+                    return Err(anyhow!(
+                        "rebuilt duplication is born-lost (probe AcquireNextFrame: {:#x}) — \
+                         topology not settled yet",
+                        e.code().0
+                    ));
+                }
+            }
+        }
         // A desktop switch can come back at a different size (e.g. the user session applies its own
         // resolution on login). Adopt it: update dimensions and drop the staging/gpu copies so they
         // reallocate. NVENC re-inits at the new size when it sees the frame.
@@ -1317,7 +1392,7 @@ impl DuplCapturer {
             self.context.CopyResource(&src, &tex);
             let _ = self.dupl.ReleaseFrame();
             self.holding_frame = false;
-            self.composite_cursor_gpu(&src)?; // onto the FP16 surface (RTV works on FP16)
+            self.composite_cursor_gpu(&src, true)?; // onto the FP16 surface (HDR: decode + nits scale)
             self.ensure_hdr10_out()?;
             let out = self.hdr10_out.clone().context("hdr10 out texture")?;
             if self.hdr_conv.is_none() {
@@ -1355,7 +1430,7 @@ impl DuplCapturer {
             self.context.CopyResource(&gpu, &tex);
             let _ = self.dupl.ReleaseFrame();
             self.holding_frame = false;
-            self.composite_cursor_gpu(&gpu)?;
+            self.composite_cursor_gpu(&gpu, false)?;
             self.last_present = Some((gpu.clone(), PixelFormat::Bgra));
             return Ok(Some(CapturedFrame {
                 width: self.width,

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

@@ -347,6 +347,20 @@ unsafe fn restore_displays(saved: &[(String, DEVMODEW)]) {
     }
 }
 
+/// Re-detach physical displays so the secure (Winlogon) desktop keeps rendering to the virtual
+/// output — for the in-session DXGI capture recovery (dxgi.rs `recreate_dupl`). The lock/UAC/login
+/// switch can re-attach a physical monitor (the secure desktop then lands on IT and our virtual
+/// output goes perpetually ACCESS_LOST — the "born-lost" storm); re-running the isolate routes the
+/// secure desktop back to the virtual output, mirroring what a fresh session's `create` does (the
+/// delta that makes a reconnect work where in-session recovery didn't). Idempotent + cheap: when
+/// nothing besides `gdi_name` is attached, [`isolate_displays`] finds nothing to detach and commits
+/// nothing — so this is safe to call on every throttled recovery tick (no display thrash).
+pub(crate) fn reassert_isolation(gdi_name: &str) {
+    unsafe {
+        let _ = isolate_displays(gdi_name);
+    }
+}
+
 unsafe fn open_device() -> Result<HANDLE> {
     let hdev = SetupDiGetClassDevsW(
         Some(&SUVDA_INTERFACE),

docs/windows-client-bootstrap.md

@@ -0,0 +1,132 @@
+# Windows native client — bootstrap handoff
+
+A handoff for an agent picking up the **native Windows punktfunk/1 client**. The host side is done
+and live-validated on a real RTX 4090; the client is the remaining piece. This doc is the concrete
+starting point: the locked decisions, the reference code to port, the stack swaps, the dev loop, and
+the gotchas. Read it top to bottom, then start at **Phase 1** (de-risk Reactor first).
+
+## What we're building
+
+A native Windows client that connects to a punktfunk/1 host (`serve --native` / `m3-host`), decodes
+HEVC, presents it low-latency, plays Opus audio, and captures local mouse/keyboard/gamepad to send
+back — i.e. the Windows analogue of the **GTK4 Linux client** (`crates/punktfunk-client-linux`),
+which is the architectural template. The Windows client is close to a 1:1 port of the Linux client
+with the platform layers swapped.
+
+## Locked decisions (from the Windows-host/client plan, `docs/windows-host.md` + project memory)
+
+- **Pure Rust.** `windows-rs` + **Windows App SDK "Reactor"** (WinUI 3 from Rust, merged windows-rs
+  PR #4479). No C++/C#. De-risk Reactor + `SwapChainPanel` FIRST — it's the only novel/uncertain
+  piece; everything else is a known-good port.
+- **Links `punktfunk-core` directly** (Cargo path dep, `features = ["quic"]`) — **no C ABI**, exactly
+  like the GTK client. `NativeClient` is already `Sync` (mutexed plane receivers), so it drops into a
+  UI app cleanly. The C ABI (`punktfunk_connect` + `next_au`/`next_audio`/`next_rumble`/`next_hidout`/
+  `send_input`/`send_rich_input`) is the *Apple* path; the native Rust clients call
+  `crates/punktfunk-core/src/client.rs` (`NativeClient`) methods directly.
+- **Video widget = WinUI 3 `SwapChainPanel`** (built-in), fed a D3D11 swapchain via
+  `ISwapChainPanelNative::SetSwapChain`.
+- **Decode = FFmpeg-next + D3D11VA** (HEVC; **Main10** for 10-bit/HDR — see below).
+- **Audio playback = WASAPI render** + Opus decode (`opus` crate, vendors libopus via cmake; set
+  `CMAKE_POLICY_VERSION_MINIMUM=3.5`).
+- **Input capture→send**: the client captures LOCAL input and sends it. Mouse (abs + relative) +
+  keyboard via the **inverse VK table** (port `keymap.rs`); gamepad via **SDL3** (already a workspace
+  dep, cross-platform) → `NativeClient::send_input`/`send_rich_input`. (`SendInput`/`ViGEm` are
+  HOST-side injection — not used by the client.)
+- **Discovery = `mdns-sd`** (cross-platform, browses `_punktfunk._udp`).
+- **Trust = shared client identity + SPAKE2 PIN pairing + TOFU** (port `trust.rs`; same identity
+  files/logic as the other native clients).
+
+## The reference: `crates/punktfunk-client-linux/src/`
+
+Port these files (near 1:1; only the platform layers change):
+
+| Linux file | Role | Windows swap |
+|---|---|---|
+| `main.rs` / `app.rs` | app shell, lifecycle | WinUI 3 `App`/`Window` via Reactor |
+| `ui_hosts.rs` | host list / connect screen | WinUI 3 page |
+| `ui_settings.rs` | settings | WinUI 3 page |
+| `ui_stream.rs` | the streaming view | WinUI 3 page hosting `SwapChainPanel` |
+| `video.rs` | FFmpeg decode + present | FFmpeg **D3D11VA** → D3D11 swapchain in `SwapChainPanel` |
+| `audio.rs` | Opus decode + playback | **WASAPI render** (was PipeWire) |
+| `session.rs` | `NativeClient` connect + plane pumps | **reuse almost verbatim** (core is cross-platform) |
+| `trust.rs` | identity, PIN, TOFU | **reuse almost verbatim** |
+| `discovery.rs` | mDNS browse | **reuse verbatim** (`mdns-sd`) |
+| `keymap.rs` | inverse VK table | reuse; Windows VK is the native source so this is *simpler* |
+| `gamepad.rs` | SDL3 pad capture + rumble/feedback | **reuse almost verbatim** (SDL3 is cross-platform) |
+
+`session.rs`, `trust.rs`, `discovery.rs`, `keymap.rs`, `gamepad.rs` are mostly platform-neutral
+(they touch `punktfunk-core` + SDL3 + mdns, all cross-platform) — expect to reuse them with minimal
+changes. The real work is `video.rs` (D3D11VA + swapchain), `audio.rs` (WASAPI), and the WinUI shell.
+
+## 10-bit + HDR (NEW — landed this session, the client MUST handle it)
+
+The host now negotiates and emits **HEVC Main10 + BT.2020 PQ HDR10** when the captured desktop is
+HDR (and 10-bit SDR Main10 when negotiated). The Apple client already does the matching present; the
+Windows client should mirror it:
+
+- **Advertise caps** in the `Hello`: `video_caps = VIDEO_CAP_10BIT | VIDEO_CAP_HDR`
+  (`crates/punktfunk-core/src/quic.rs`). The host enables 10-bit only if the client advertised it.
+  (The native-client connector in `client.rs` currently hardcodes `video_caps: 0` with a TODO —
+  thread the real caps through when you wire decode; or detect HDR purely in-band, see next.)
+- **Detect HDR in-band** from the HEVC VUI (transfer characteristics = SMPTE ST 2084 / PQ), exactly
+  like the Apple client's `VideoDecoder.isHDRFormat` (`clients/apple/Sources/PunktfunkKit/`). This
+  handles a mid-session HDR toggle without renegotiation. `Welcome.bit_depth` (8/10) is also available.
+- **Decode** Main10 → **P010** (10-bit) via D3D11VA.
+- **Present HDR**: swapchain in `DXGI_FORMAT_R10G10B10A2_UNORM` (or `R16G16B16A16_FLOAT`),
+  `IDXGISwapChain3::SetColorSpace1(DXGI_COLOR_SPACE_RGB_FULL_G2084_NONE_P2020)` +
+  `SetHDRMetaData` for HDR10; the host's stream is BT.2020 PQ, so present PQ. For SDR, the existing
+  `DXGI_FORMAT_B8G8R8A8_UNORM` + BT.709 path. (The host-side HDR conversion math is in
+  `crates/punktfunk-host/src/capture/dxgi.rs` `HDR_PS`/`HdrConverter` if you need the inverse.)
+
+## Dev boxes
+
+- **No-GPU dev box (UI + connect + software decode):** `ssh "Enrico Bühler"@192.168.1.57` — Win11 Pro
+  25H2 (build 26200), QEMU Q35, 8 vCPU/12 GB, **no working GPU** (so no NVENC, no D3D11VA hardware
+  decode — use FFmpeg software decode here; this box is for UI/connect/protocol work). Has Rust 1.96
+  MSVC, VS 2026 + VC tools + Win SDK, Win App Runtime 2.2, SudoVDA + Parsec VDD.
+- **Real-GPU box (HDR / hardware decode / end-to-end):** `ssh "Enrico Bühler"@192.168.1.174` — Win11,
+  RTX 4090, runs the host. Use it to test the client against a live HDR host.
+
+### Dev-loop gotchas (both boxes)
+
+- **Build under an ASCII path** (`C:\Users\Public\…`). The username "Enrico Bühler" has a `ü` → MSVC
+  `LNK1201` PDB-write failure under `~/Developer`.
+- **Toolchain gaps:** `winget install NASM.NASM Kitware.CMake LLVM.LLVM` (aws-lc-rs on the quic path,
+  ffmpeg-sys needs libclang).
+- **`CMAKE_POLICY_VERSION_MINIMUM=3.5`** in the build env (CMake 4 rejects libopus's old minimum).
+- **File transfer = `sftp`** (scp is broken under the PowerShell DefaultShell):
+  `printf 'put %s /C:/Users/Public/REL/PATH\n' LOCAL | sftp -b - "Enrico Bühler@192.168.1.57"` —
+  note the **leading slash** `/C:/…`. Let the VM regenerate its own `Cargo.lock` (don't transfer it).
+- **Windows clippy is stricter** than Linux CI and `cfg(windows)` code is excluded from Linux CI →
+  run `cargo clippy -p punktfunk-client-windows -- -D warnings` ON THE VM before committing.
+- Work on `main`; fetch+merge `origin/main` before pushing.
+
+## Suggested phased plan
+
+1. **De-risk Reactor (do this first).** A windows-rs Reactor (WinUI 3) hello-world that hosts a
+   `SwapChainPanel` and presents a cleared D3D11 swapchain into it. Confirm the windows-rs Reactor
+   version/API (PR #4479) and `ISwapChainPanelNative::SetSwapChain` interop. If Reactor proves too
+   raw, the fallback is `winit` + a child HWND swapchain, but try Reactor first per the decision.
+2. **Crate scaffold.** `crates/punktfunk-client-windows`, `[target.'cfg(windows)'.dependencies]`:
+   `punktfunk-core { path, features=["quic"] }`, `windows`, the Reactor crate, `ffmpeg-next`, `opus`,
+   `sdl3`, `mdns-sd`, `anyhow`, `tracing`. Mirror `crates/punktfunk-client-linux/Cargo.toml`.
+3. **Connect + control plane.** Port `session.rs` + `trust.rs`; validate headless against the 4090
+   box (`m3-host`/`serve --native`) — handshake, PIN/TOFU, plane counters — before any UI/decode.
+4. **Decode + present.** FFmpeg D3D11VA → `SwapChainPanel`. SDR (8-bit BGRA) first, then **P010 +
+   HDR colorspace** (see the HDR section).
+5. **Audio.** WASAPI render + Opus decode (port `audio.rs`).
+6. **Input.** Mouse + keyboard capture→send (port `keymap.rs`), gamepad via SDL3 (port `gamepad.rs`),
+   feedback from `next_rumble`/`next_hidout`.
+7. **Discovery + UI.** Port `discovery.rs` + `ui_hosts.rs` + `ui_settings.rs` to WinUI pages.
+
+## Key references
+
+- **Template:** `crates/punktfunk-client-linux/src/*` (the client to port).
+- **Apple HDR present** (the pattern to mirror): `clients/apple/Sources/PunktfunkKit/{VideoDecoder,
+  MetalVideoPresenter,Stage2Pipeline}.swift` — in-band PQ detection, P010 decode, EDR present.
+- **Core client API:** `crates/punktfunk-core/src/client.rs` (`NativeClient`).
+- **Protocol:** `crates/punktfunk-core/src/quic.rs` (`Hello.video_caps`, `Welcome.bit_depth`,
+  `VIDEO_CAP_10BIT`/`VIDEO_CAP_HDR`).
+- **Full Windows plan + SudoVDA/host details:** `docs/windows-host.md`.
+- **Host HDR conversion (for the inverse math):** `crates/punktfunk-host/src/capture/dxgi.rs`
+  (`HDR_PS`, `HdrConverter`) + `crates/punktfunk-host/src/encode/nvenc.rs` (BT.2020/PQ VUI).