feat(encode): AV1 on the Linux Vulkan Video encoder (real RFI)

Extend the raw Vulkan Video backend to AV1 (`VK_KHR_video_encode_av1`)
alongside HEVC, so AMD/Intel Linux hosts get the same clean-P-frame loss
recovery for AV1 that HEVC already has — no full IDR on packet loss.

ash 0.38.0+1.3.281 predates the AV1-encode extension (finalized in Vulkan
1.3.290) and bumping ash breaks the SDL/Vulkan client (it drops the
lifetime on AllocationCallbacks, which sdl3-sys still generates). So the
AV1-encode structs/flags/enums are vendored host-only in
`encode/linux/vk_av1_encode.rs`, copied verbatim from ash-master's
generated code and chained into ash's generic video-encode calls via raw
p_next — the common StdVideoAV1* types (from AV1 decode) are reused from
ash 1.3.281.

`vulkan_video.rs` gains a parallel AV1 path: AV1 Main profile/caps/session
(+ max-level session-create), a bit-packed sequence-header OBU + per-frame
temporal-delimiter framing (Vulkan AV1 encode, unlike H26x, emits only the
frame OBU), and per-frame StdVideoEncodeAV1PictureInfo with the RFI
reference model — a normal P inherits CDF context from its reference for
compression, while an IDR or recovery anchor sets primary_ref_frame=NONE +
error_resilient_mode so it decodes independent of the (possibly lost)
frames since its reference. HEVC recording is unchanged; the shared CSC /
ring / DPB-barrier pipeline is reused as-is. Codec routing in
`open_video_backend` extends the HEVC arm to HEVC|AV1.

The seq header enables only order-hint (+128px superblocks per caps),
matching FFmpeg's proven Vulkan AV1 config — enabling CDEF/restoration made
VCN emit frame-header sections our seq header didn't match, desyncing every
inter frame.

Headless-validated on real RADV (780M): open + 6-frame encode (I P P P P P)
decodes 0-error on both dav1d and ffmpeg/cbs; the RFI recovery anchor at
frame 4 is a clean P (not IDR), and dropping the "lost" frame 3 still
decodes clean (re-anchored to frame 2). HEVC smoke unchanged (no
regression). `cargo clippy --features vulkan-encode -- -D warnings` and the
no-feature build both green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/punktfunk-host/src/encode.rs

@@ -536,12 +536,13 @@ fn open_video_backend(
         // the Vulkan backend imports the dmabuf and does its own 8-bit 4:2:0 CSC.
         let open_amd_intel = || -> Result<Box<dyn Encoder>> {
             #[cfg(feature = "vulkan-encode")]
-            if codec == Codec::H265 && vulkan_encode_enabled() {
+            if matches!(codec, Codec::H265 | Codec::Av1) && vulkan_encode_enabled() {
                 match vulkan_video::VulkanVideoEncoder::open(codec, width, height, fps, bitrate_bps)
                 {
                     Ok(e) => {
                         tracing::info!(
-                            "Linux Vulkan Video HEVC encode (real RFI via DPB reference slots) — \
+                            codec = ?codec,
+                            "Linux Vulkan Video encode (real RFI via DPB reference slots) — \
                              set PUNKTFUNK_VULKAN_ENCODE=0 for libav VAAPI"
                         );
                         return Ok(Box::new(e) as Box<dyn Encoder>);
@@ -581,9 +582,9 @@ fn open_video_backend(
             "vulkan" | "vulkan-video" => {
                 #[cfg(feature = "vulkan-encode")]
                 {
-                    if codec != Codec::H265 {
+                    if !matches!(codec, Codec::H265 | Codec::Av1) {
                         anyhow::bail!(
-                            "the Vulkan Video encoder is HEVC-only; the session negotiated {codec:?}"
+                            "the Vulkan Video encoder supports HEVC + AV1; the session negotiated {codec:?}"
                         );
                     }
                     vulkan_video::VulkanVideoEncoder::open(codec, width, height, fps, bitrate_bps)
@@ -1251,6 +1252,13 @@ mod vaapi;
 #[cfg(all(target_os = "linux", feature = "vulkan-encode"))]
 #[path = "encode/linux/vulkan_video.rs"]
 mod vulkan_video;
+// Vendored `VK_KHR_video_encode_av1` bindings (host-only) — the AV1 encode structs our pinned
+// `ash 0.38.0+1.3.281` predates (finalized Vulkan 1.3.290). Copied verbatim from ash-master's
+// generated code rather than bumping `ash` (which breaks the SDL/Vulkan client). Consumed by
+// `vulkan_video.rs` via `super::vk_av1_encode`.
+#[cfg(all(target_os = "linux", feature = "vulkan-encode"))]
+#[path = "encode/linux/vk_av1_encode.rs"]
+mod vk_av1_encode;
 
 #[cfg(test)]
 mod tests {