perf(pyrowave): pool encoder scratch buffers + fix client parser O(n²) — lift the 2.5 Gbps wall

Real-world PyroWave streaming maxed ~2.5 Gbps with sagging fps while raw
transport does 4.8. Root-caused to serial per-frame paths at BOTH ends
(the transport was never the limit); this fixes the two dominant ones.

Host (vendored shim, patch 0004): pyrowave_encoder_encode_gpu_synchronous
allocated four Vulkan buffers (meta + bitstream, Device + CachedHost) on
EVERY frame. At 240 fps with MB-scale bitstreams that per-frame allocator
churn stalled the encode itself. Pool them on the encoder and reuse across
frames (recreate only on a size grow); the sizes are session-fixed, so it
is pure reuse after frame 1. On an RTX 4090 the 5120x1440 submit+fence-wait
drops ~15 ms -> ~1 ms, i.e. the host serial ceiling goes 64 -> 1025 fps
(444+HDR 44 -> 614). Safe under the synchronous encode model; re-validated
by pyrowave_win_smoke (Windows) and pyrowave_smoke/_444 (Linux). Applies to
both host encoder paths (they share the shim).

Client (Apple Metal decoder): WaveletBitstream.parse reserved the payload
buffer per packet (reserveCapacity(count + words), an exact realloc each of
~3000 packets/frame => O(n²)) and copied word-by-word. Reserve once up
front and memcpy each packet's coefficients in one shot (all Apple
platforms are little-endian, so the wire's LE u32s land verbatim; memcpy is
alignment-free). 5.44 ms -> 0.055 ms per 1.44 MB frame (25x); byte-identical
(parser unit tests + golden-frame PSNR unchanged).

Also:
- native.rs: PUNKTFUNK_PYROWAVE_MAX_MBPS caps PyroWave's open-loop Automatic
  bitrate pin for hosts on a constrained link (unset => no cap; an explicit
  client rate bypasses it). The pin is all-intra + ABR-off, so at a high
  pixel rate it can outrun the fabric (4:4:4+HDR 5120x1440@240 pins ~5.3
  Gbps, over a 5 GbE link) and the overshoot just becomes loss.
- pf-encode caps(): report the real opened chroma instead of a hardcoded
  4:2:0 default, so a genuine 4:4:4 session no longer trips the spurious
  "encoder chroma disagrees with the negotiated Welcome" warn. Also fix a
  latent Windows reset() that rebuilt at 4:2:0 for a 4:4:4 session.

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

crates/pf-encode/src/enc/linux/pyrowave.rs

@@ -1165,9 +1165,14 @@ impl Encoder for PyroWaveEncoder {
     }
 
     fn caps(&self) -> EncoderCaps {
-        // All defaults: no RFI (meaningless — every frame is intra), no HDR (8-bit SDR codec),
-        // no intra-refresh wave (ditto). 4:2:0 only until the 4:4:4 ride-along (plan §6).
-        EncoderCaps::default()
+        // No RFI / no intra-refresh wave (every frame is intra). Report the real opened chroma so
+        // the session glue's post-open cross-check stays quiet on a genuine 4:4:4 session — a
+        // hardcoded `default()` here mis-reports a 4:4:4 open as 4:2:0 and fires a spurious
+        // "chroma disagrees with the negotiated Welcome" warn.
+        EncoderCaps {
+            chroma_444: self.chroma444,
+            ..EncoderCaps::default()
+        }
     }
 
     fn poll(&mut self) -> Result<Option<EncodedFrame>> {

crates/pf-encode/src/enc/windows/pyrowave.rs

@@ -549,8 +549,14 @@ impl Encoder for PyroWaveEncoder {
     }
 
     fn caps(&self) -> EncoderCaps {
-        // All defaults: no RFI (every frame is intra), no HDR (8-bit SDR codec), 4:2:0 only.
-        EncoderCaps::default()
+        // No RFI (every frame is intra). Report the real opened chroma so the session glue's
+        // post-open cross-check stays quiet on a genuine 4:4:4 session (this codec gained 4:4:4
+        // after the caps() default was written — a hardcoded `default()` here mis-reports a 4:4:4
+        // open as 4:2:0 and fires a spurious "chroma disagrees with the negotiated Welcome" warn).
+        EncoderCaps {
+            chroma_444: self.chroma444,
+            ..EncoderCaps::default()
+        }
     }
 
     fn poll(&mut self) -> Result<Option<EncodedFrame>> {
@@ -567,7 +573,13 @@ impl Encoder for PyroWaveEncoder {
                 device: self.pw_dev,
                 width: self.width as i32,
                 height: self.height as i32,
-                chroma: pw::pyrowave_chroma_subsampling_PYROWAVE_CHROMA_SUBSAMPLING_420,
+                // Rebuild at the session's real chroma — a hardcoded 420 here would leave a 4:4:4
+                // session's full-res chroma plane + CSC feeding a 4:2:0 pyrowave encoder.
+                chroma: if self.chroma444 {
+                    pw::pyrowave_chroma_subsampling_PYROWAVE_CHROMA_SUBSAMPLING_444
+                } else {
+                    pw::pyrowave_chroma_subsampling_PYROWAVE_CHROMA_SUBSAMPLING_420
+                },
             };
             let mut enc: pw::pyrowave_encoder = std::ptr::null_mut();
             let r = pw::pyrowave_encoder_create(&einfo, &mut enc);