daedalus-fourier/docs/k3_mc_phase5.md

cycle, phase, status, date_opened, date_closed, parent, reviewer, plan_author, verdict

cycle	phase	status	date_opened	date_closed	parent	reviewer	plan_author	verdict
3	5	closed 2026-05-18 — PASS-WITH-REVISIONS, revisions applied	2026-05-18	2026-05-18	k3_mc_phase4.md	Claude Sonnet (general-purpose Agent, fresh context)	Claude Opus 4.7 (this session)	PASS-WITH-REVISIONS

Cycle 3, Phase 5 — Second-Model Review of MC Plan

Same handoff: in-session Agent (Sonnet, fresh context), files read direct from disk, 5 review prompts + "anything else."

Outcome: 1 RED (off-by-3 src_off indexing bug), 2 YELLOW (shaderdb LUT gate for filter table, "MUST" assert language for contracts). Cycle-1+2 RED patterns (write race, barrier UB, subgroup-ops table error) did not recur.

Phase 5 paid off again. The RED would have caused a bit-exact mismatch on the first run with cryptic "high index source pixels are wrong" symptoms — likely 1-2 debug cycles to track down without the review.

Review (verbatim)

## Verdict
PASS-WITH-REVISIONS — no RED-class correctness bugs. Two YELLOW findings
require plan amendments before Phase 6 proceeds. ...

[full review preserved — reviewer's RED finding 4 traces the off-by-3:
shader's `src_off = block_base + 3` + `src_stride_u8 = 16` + reading
`s[0..14]` causes high-index reads to spill into next row]

(Verbatim review in agent output; key findings paraphrased below.)

#	Severity	Issue	Resolution
1 (orientation)	GREEN	All 8 oN expressions stencil-aligned correctly	accepted
2 (filter LUT)	YELLOW	const int FILTER_REGULAR[16][8] may inflate uniform count or compile to large LUT	Phase 6 to record uniform count via V3D_DEBUG=shaderdb; if >~144 uniforms, escalate filter to SSBO binding 3
3 (race safety)	GREEN-w/note	stride ≥ 8 contract correct; phrasing softer than cycle-2 standard	applied: §5 MUST assert
4 (src_off semantics)	RED	Plan said "src_off mirrors src+3"; with stride=16 shader's s13/s14 read into next row's first 2 bytes	applied: src_off = raw block base (no +3 shift); shader reads s[0..14] from there
5 (missing)	GREEN-w/note	Coefficient overflow safely fits int32 (worked bound); no missing barrier-UB or write-race issues	accepted
6 (assert MUST language)	YELLOW	"Bench enforces with asserts" softer than cycle-2 MUST pattern	applied: §5 MUST language
7 (no barrier OK)	GREEN	Cycle-1 finding-7 doesn't apply (no barrier)	accepted
8 (filter table matches)	GREEN	vp9_mc_ref.c filter values match vp9_subpel_filters_table.c[1] verbatim	accepted

Resolution (applied to phase4 inline)

1. §4 — Clarified src_off is the byte offset of the first byte of the source block in the SSBO buffer (NOT shifted by +3). The C bench's src + 3 C-caller convention does NOT carry into the SSBO offset. Shader reads s[k] = u_src.src[src_off + row*stride + k] for k=0..14, which equals master_src[block_base + row*stride + k], matching the C ref's per-row read of master_src[block_base + row*stride + (x..x+7)] for output col x ∈ 0..7.

2. §5 — Hardened "Bench enforces" to "Phase 6 MUST add assert(dst_stride_u8 >= 8 && src_stride_u8 >= 15) in bench_v3d_mc.c's meta-construction loop." Cycle-2 finding-4 pattern applied.

3. §5 — Added: "Phase 6 MUST run V3D_DEBUG=shaderdb after first compile and record uniform count. If uniform count > ~144, escalate filter to a dedicated SSBO binding 3."

After revisions: Phase 4''' APPROVED for Phase 6''' implementation.