feat(clients/windows): D3D11VA hardware decode in the session client — Vulkan chain becomes vulkan → d3d11va → software

The vendor-agnostic DXVA path for GPUs without Vulkan Video (Intel's Windows driver foremost,
which previously landed on CPU decode). Ported from the retired WinUI presenter's decoder with
its Intel-safe discipline intact (decode pool stays libavcodec-derived — a hand-built pool
broke Intel at the first SubmitDecoderBuffers), on a decode device LUID-matched to the
presenter's adapter.

Hand-off is a ring of shareable BGRA8 textures (SHARED_NTHANDLE | SHARED_KEYEDMUTEX) filled by
the fixed-function ID3D11VideoProcessor (NV12/P010 → BGRA8, colour spaces from the per-frame
CICP; PQ is tone-mapped to SDR by the processor — HDR-first boxes take Vulkan Video). BGRA is
deliberate: importing a multiplanar NV12 D3D11 texture device-losts on NVIDIA however it is
consumed (plane-view sampling and DMA copy both validation-clean, both TDR — bisected), while
single-plane RGBA D3D11↔Vulkan interop is the path Chromium/ANGLE exercise on every driver.
The presenter imports a slot's NT handle per frame (VK_KHR_external_memory_win32, gated on the
spec-required external-format probe) and blits it into the video image — no CSC pass; the DXGI
keyed mutex (key 0 both sides, drop-tolerant) is the cross-API lock and visibility barrier.

Verified live vs a real host at 5120x1440@240 HEVC on an RTX 4090: 240 fps, e2e 2.7/3.0 ms
p50/p95 under the Khronos validation layer — parity with Vulkan Video (2.6 ms); auto still
resolves vulkan on NVIDIA. PUNKTFUNK_DECODER=d3d11va forces it; import/present failures demote
to software on the existing streak contract.

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

crates/pf-presenter/src/run.rs

@@ -817,6 +817,47 @@ fn run_inner(mut opts: SessionOpts, mut mode: ModeCtl) -> Result<Option<Outcome>
                         }
                         false
                     }
+                    // D3D11VA: shared-texture import, same gate + failure-streak
+                    // demotion contract as the dmabuf path.
+                    #[cfg(windows)]
+                    DecodedImage::D3d11(d) if presenter.supports_d3d11() && !st.dmabuf_demoted => {
+                        st.hdr = d.color.is_pq();
+                        match presenter.present(
+                            &window,
+                            FrameInput::D3d11(d),
+                            overlay_frame.as_ref(),
+                        ) {
+                            Ok(p) => {
+                                st.hw_fails = 0;
+                                p
+                            }
+                            Err(e) => {
+                                st.hw_fails += 1;
+                                tracing::warn!(error = %format!("{e:#}"), fails = st.hw_fails,
+                                    "hardware present failed");
+                                if st.hw_fails >= 3 && !st.dmabuf_demoted {
+                                    st.dmabuf_demoted = true;
+                                    tracing::warn!("demoting the decoder to software");
+                                    st.force_software.store(true, Ordering::Relaxed);
+                                }
+                                false
+                            }
+                        }
+                    }
+                    #[cfg(windows)]
+                    DecodedImage::D3d11(_) => {
+                        // No import extensions on this device (or already demoted) — the
+                        // pump rebuilds the decoder as software; frames flow again soon.
+                        if !st.dmabuf_demoted {
+                            st.dmabuf_demoted = true;
+                            tracing::warn!(
+                                "no win32 external-memory import on this device — demoting \
+                                 the decoder to software"
+                            );
+                            st.force_software.store(true, Ordering::Relaxed);
+                        }
+                        false
+                    }
                     // Vulkan-Video: decoded on the presenter's own device — present is
                     // views + CSC, no import step to gate on. Same failure-streak
                     // demotion contract as the dmabuf path.