Phase 3 Candidate K executed: H-D (slot rotation) ELIMINATED via
instrumented bind+read site logging. Slot v4l2_index matches at
BeginPicture and at vaGetImage for every surface; destination_data[0]
matches slot->map[0]. No rotation mismatch.
H-A/B/C/D all eliminated. H-E (kernel-side hantro VP8 partial-write)
confirmed by elimination. The libva backend submits correct controls,
correct slice bytes, correct slices_size, correct slot indices.
Kernel writes erratic partial content (per-frame Y plane transitions
at row 536, 24, ... — not a clean buffer-size truncation, not slot
rotation).
iter6 close PARTIAL: 5 of 6 Phase 1 criteria PASS; criterion 1
(libva_vp8 == kdirect) PARTIAL — kernel-side fix needed, out of
iter6's locked backend-only scope.
No patches landed. Fresnel substrate unchanged: fork tip 70196f8,
backend SHA 2c6ff82c... (identical to iter5b-β close).
Net deliverable: Phase 3 narrowing reduces Bug-6 hypothesis space
from 5 to 1. Future iter7+ (or kernel-agent campaign) picks up the
kernel-side investigation.
Pattern recognized: iter2 HEVC transitive PASS masked Bug 5;
iter3 VP8 transitive PASS masked Bug 6. Both surfaced under direct
verification post-iter5b-β. Transitive proofs against ONE artifact
(control payload) don't catch bugs in OTHER artifacts.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
