S1c `nvenc_cuda_split_subframe_pair_reconfigure`: the leg S1a/S1b excluded. Both
pinned sub-frame OFF to isolate the split variable, but a real HEVC arbitration
cannot -- split and sub-frame are mutually unsupported there, so engaging split
means flipping enableSubFrameWrite in the same breath, a second init param and
the one the reconfigure path deliberately pins. RESULT on .21: the PAIR moves in
place, accepted, ZERO IDRs, both directions.
It also pins the invariant that makes this safe to build on: `subframe_chunks` is
latched ONLY in the init path (~line 1625) and is NOT recomputed by
reconfigure_bitrate, so a caller flipping sub-frame in place must clear it too or
supports_chunked_poll keeps reporting true and poll_chunk busy-polls its whole
budget every AU against a numSlices that never advances. The test performs the
correct sequence and asserts the state stays coherent, so WP3 has a worked
example rather than a warning.
`nvenc_cuda_auto_split_with_subframe`: the D5 confirm -- the one claim in the
design's defect list that was only ever inferred. The driver reports no "mode I
actually chose", so it is settled by timing, at 4K where the gap is ~2x.
RESULT: AUTO (env unset) + sub-frame 4904 us/frame, DISABLE + sub-frame 5062,
TWO_FORCED without sub-frame 3464. AUTO sits 158 us from DISABLE and 1440 from
TWO_FORCED ⇒ D5 CONFIRMED: plain AUTO does not split while sub-frame is on, so
the resolver's AUTO fallthrough reads as "let the driver decide" and means
"never split".
⚠ TRAP, hit on this test's first run and now documented in it: the env knob
CANNOT express plain AUTO. `0` is DISABLE and `1` is AUTO_FORCED, and
resolve_split_subframe counts AUTO_FORCED as forced, so passing `1` silently
disarms sub-frame and measures a different configuration entirely -- which
produced a spurious "D5 REFUTED". Plain AUTO is only reachable as the resolver's
fallthrough with the env unset. The leg now asserts sub-frame resolved TRUE, so
the test can no longer answer the wrong question quietly.
Verified on .21: clippy --features nvenc --all-targets -D warnings clean, all 4
spikes green, the normal 54-test suite unaffected, cargo fmt --all --check clean.
enricobuehler
70b81ac3d7