Address two max-effort code-review findings on PR #2056 not covered by
the earlier review-gap commit:
- captureFrameToBufferPipelined's static-dedup reuse branch never
advanced session.lastEncodeResultFrame, unlike its sibling real-capture
branches. The gap-check window is computed from that watermark, so
every consecutive reuse in a static run rescanned an ever-widening
window instead of just the newest frame — O(n^2) total work over a
long static stretch instead of O(n).
- The "single-threaded, no race" justification on the shared
parallelGuard closure was wrong: the guard has real internal await
points (recapture, PSNR) between reading and writing its
sizes/absFloor/acceptedSmall state, so concurrent workers' calls do
interleave there (confirmed). Replaced with the actual reason it's
safe: absFloor only ratchets down, sizes is append-only and
order-independent for the median, and acceptedSmall's fast path
re-validates by exact byte-equality regardless of which worker wrote
the reference buffer.
Vance Ingalls
381887541f