feat(linux/vulkan-encode): default-on native NV12 capture + RGB true-extent

Flip both zero-copy levers from opt-in to default:

- The capture negotiation now PREFERS gamescope's producer-side NV12 pod by
  default (PUNKTFUNK_PIPEWIRE_NV12=0 restores the packed-RGB negotiation).
  Codec-aware gating rides a new OutputFormat::nv12_native ->
  ZeroCopyPolicy::native_nv12_session edge resolved by the host facade from
  the session plan (pf_encode::linux_native_nv12_ok): only H265/AV1 sessions
  whose backend can open the raw Vulkan Video encoder ever see the NV12 pod
  -- an H264/Moonlight session (libav VAAPI, which would misread the
  two-plane buffer) keeps today's BGRx negotiation, as do the
  GameStream-resolve and portal-mirror paths, PyroWave, and NVENC prefs.
- RGB-direct's unaligned modes default to the true-extent direct import
  (PUNKTFUNK_VULKAN_RGB_TRUE_EXTENT=0 restores the padded-copy staging).
  Guarded-tested on Van Gogh with the kernel journal watched: clean, and at
  5.38 ms p50 the fastest 1080p encode path measured on that hardware. The
  EFC only exists on Mesa >= 26, where the codedExtent-driven session_init
  padding is guaranteed (verified back to Mesa 24.2).

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

crates/pf-capture/src/lib.rs

@@ -259,6 +259,12 @@ pub struct ZeroCopyPolicy {
     /// passthrough (like the VAAPI backend) instead of the EGL→CUDA import whose payloads only
     /// NVENC can consume. Per-session (the codec is negotiated), unlike `backend_is_vaapi`.
     pub pyrowave_session: bool,
+    /// THIS session's encoder can ingest a producer-native NV12 capture (the Linux raw Vulkan
+    /// Video backend on an H265/AV1 session — resolved by the host facade via
+    /// `pf_encode::linux_native_nv12_ok`). Gates whether the negotiation PREFERS gamescope's
+    /// producer-side NV12 pod: libav VAAPI (H264's backend) would misread the two-plane buffer,
+    /// so H264/GameStream/PyroWave sessions must never see NV12 frames.
+    pub native_nv12_session: bool,
     /// The PyroWave encoder's Vulkan-importable dmabuf modifiers for the capture's packed-RGB fourcc,
     /// resolved when the session encodes PyroWave (the passthrough advertises them so Mutter+NVIDIA,
     /// which allocates tiled-only, still negotiates zero-copy). Empty otherwise.

crates/pf-capture/src/linux/mod.rs

@@ -2086,22 +2086,26 @@ mod pipewire {
         // PyroWave session (the wavelet encoder's own Vulkan device, any vendor) → hand the raw
         // dmabuf straight to the encoder.
         let vaapi_passthrough = zerocopy && !force_shm && importer.is_none() && raw_passthrough;
-        // Bring-up gate for producer-side NV12. Gamescope offers a one-fd LINEAR NV12 image when
-        // the consumer asks for it; keep this opt-in until the live Vulkan import path is proven.
-        // Raw passthrough is required because CUDA/PyroWave expect packed RGB, and 4:4:4/HDR must
-        // not be silently subsampled/downconverted.
-        let prefer_native_nv12 = std::env::var("PUNKTFUNK_PIPEWIRE_NV12").as_deref() == Ok("1")
+        // Producer-side NV12 (default-on; PUNKTFUNK_PIPEWIRE_NV12=0 escapes): gamescope offers a
+        // one-fd LINEAR NV12 image when the consumer asks — its compositor pass does the RGB→YUV,
+        // and the Vulkan Video encoder imports the buffer as its encode source directly (no host
+        // CSC at all). `native_nv12_session` restricts this to sessions whose encoder can ingest
+        // it (Linux vulkan-encode H265/AV1 — never H264/libav-VAAPI, GameStream-resolve, or
+        // PyroWave, whose Vulkan compute CSC ingests packed RGB only). Raw passthrough is
+        // required because the CUDA importer expects packed RGB, and 4:4:4/HDR must not be
+        // silently subsampled/downconverted. Non-NV12 compositors (KWin/GNOME) simply match the
+        // packed-RGB fallback pod.
+        let prefer_native_nv12 = std::env::var("PUNKTFUNK_PIPEWIRE_NV12").as_deref() != Ok("0")
+            && policy.native_nv12_session
             && backend_is_vaapi
             && vaapi_passthrough
-            // PyroWave rides the same raw passthrough but its Vulkan compute CSC ingests packed
-            // RGB only — native NV12 would feed it an unreadable two-plane image.
             && !policy.pyrowave_session
             && !want_444
             && !want_hdr;
         if prefer_native_nv12 {
             tracing::info!(
-                "PUNKTFUNK_PIPEWIRE_NV12=1: preferring gamescope producer-side NV12 LINEAR \
-                 DMA-BUF (no host RGB CSC)"
+                "zero-copy: preferring gamescope producer-side NV12 LINEAR DMA-BUF (no host \
+                 RGB CSC; PUNKTFUNK_PIPEWIRE_NV12=0 restores the packed-RGB negotiation)"
             );
         }
         // Modifiers our import stack handles for BGRx: the EGL-importable (tiled) set, plus LINEAR