trim_decoders dropped the decoders it took from idle caches while the requesting cache's lock was held. Dropping a decoder can block (a VideoToolbox session waits for its frames in flight), so the render path paid that latency under the lock. trim_decoders now returns the released decoders and frame_late keeps them in a local declared before its lock guard, so they drop after the guard on every return path; the cap is enforced exactly as before.
New tests/pool_bitexact.rs: primes the frame pool with 0xAA-filled plane buffers, then decodes an H.264 fixture into them; every frame must match ffmpeg bit for bit, and the pool must report the reuse.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
