[AdaWorldAPI]

Summary

Board-only closeout for the U9 arc (#388, #389, #390 and #391, all merged). It makes no code change.

.claude/board/EPIPHANIES.md

Two entries are added at the top, and both pass the admission gate: they are new, load-bearing and durable.

1. Signed magnitude is schoolbook arithmetic. The sign is a routing decision (plane_a ^ plane_b). Multiplication is an exact split, |b| = low7 - top, built from AND and XOR only. Accumulation is a fold, flushed to i64. The byte-dot built this way (B) costs 3.05 ns per 64 values on AVX-512 VNNI. The widen-to-f32 route (A) costs 7.6 – 7.8 ns there, and 75 – 81 ns on AVX2.
2. Exactness past a lane's width is a carry count, not a wider type. A wrapping 16-bit low plus a count of carries into high replaces A's f32 accumulation and is about 10% cheaper in L1. LLVM lowers the bit-logic carry rules to vpternlogq. Lazy EMPTY/FULL flags in bit-sliced counters never pay: they cost 1.6 – 2.2 ns per column, against 0.5 ns for the eager ripple.

The review lessons are not filed as epiphanies, because each one would not matter if the mistake had never happened:

• the padded Vec<Block> layout;
• benchmarks that consumed only part of their prepared data;
• the stale-word fixture.

.claude/blackboard.md

This adds the closeout and the open fruit list, each item with a gate:

• Low:
  • U1: wire sum8_u8_add_masked into candidate E.
  • U2: explain why streamed AVX2 B is slower than L1 by more than the extra bytes.
  • U3: measure on NEON and wasm.
• High:
  • U4: a facade word that turns the sign plane into ±1 bytes.
  • U5: the AVX2 mask_blend per-lane loop.
• Heavy:
  • U6: a U8x64 -> I8x64 view. This needs an operator ruling, because the facet-stride rule forbids u8/i8 mixing.
  • U7: recall on a real TurboVec-U9 index.

It also records two exclusions, not to be reopened without new evidence:

• bit-plane multiplication as a replacement for B;
• lazy flags in bit-sliced counters.

---

Generated by Claude Code

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-29T23:06:20.094417Z	f507e20	Draft marked ready

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