Phase 3 redefined Bug 4 to partial-fill (not inter race). Three distinct
per-codec signatures (VP9 correct, HEVC zero, H.264 partial-leak) can't
be explained by a single hypothesis. Phase 4 commits to γ first: a
~30 LOC env-gated diagnostic dump in RequestSyncSurface that fires
after CAPTURE DQBUF, prints first/last 32 bytes of each destination_data
plane and a non-zero-count of the first 1024 bytes.
γ definitively distinguishes "kernel didn't write" from "libva mis-reads"
from "slot binding wrong". Phase 4b targeted fix follows γ's outcome.
Out of scope: per-codec H.264 control-fill changes (gated on γ's
findings), VP9/VP8/HEVC/MPEG-2 paths, kernel patches.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
