Captured-pair gates: score fresh runs against an oracle-side-only top-K golden instead of the self-anchor

Row: BACKEND-TENSTORRENT-KEEPQUANT

Problem

The captured-pair gates (the qwen3.5 Q4_K_M TT vehicle today; the same
ladder shape in the qwen3/mistral gates) pin two functions of OUR engine's
numerics: the exact ids anchor (self-match REQUIRE) and a per-capture
teacher-forced gap golden. Every ULP-level shift — a tt-metal pin bump, a
kernel change — re-rolls the ~51/256 near-tie cells and turns the gate red,
forcing a golden refresh. The refresh itself is where the process failed on
2026-09-12: an off-recipe re-derivation wrote f32-grain gaps that
manufactured four band violations and nearly drove a kNearTieMnats
widening (recorded in .agents/specs/tenstorrent-keepquant.md, Evidence).
The pinned-recipe truth was max gap 250 mnats, 0 cells above band — the
engine was fine; the refresh path was not.

Proposed shape

Commit an oracle-side-only golden: per prompt cell, the pinned oracle's
top-K logprobs under the ORACLE's own greedy prefix — stable under our code
changes, so it never re-captures for engine-side reasons. The gate scores
the fresh engine run against the committed top-K up to the first
divergence and fails only a confident divergence (gap above band, or our
token outside top-K). Near-tie flips pass with a recorded margin. The
self-anchor exact REQUIRE becomes an advisory MESSAGE recording the
re-roll. At the decision cell this is exactly the bar the gap script's own
header declares ("is our token, given our exact prefix, one the oracle
cannot confidently separate"); post-flip cascade cells are cross-context
and uninformative today anyway.

Why not now

The verified pair plus the provenance-hardened re-derivation path
(scripts/qwen35-q4km-neartie-gap.sh) lands in #2959's flow. This
redesign is a semantic checker change: it needs its own spec, a
red-before demonstration (a ULP re-roll failing today's anchor),
mutation evidence that a real divergence still fails, and fresh review.

Start with .agents/specs/tenstorrent-keepquant.md and scripts/qwen35-q4km-neartie-gap.sh, then review the verified-pair and #2959 flow. Define the checker change with its own spec, demonstrate a red-before ULP re-roll, and provide mutation evidence that a real divergence still fails before review.