feat(gate): capture overrides the test-presence diff heuristic (#3502)

[veksen]

What

The test-presence gate (evaluateTestPresence) is a pure diff heuristic — it flags a data-access change when no related data-layer test changed alongside it, matching "related" by directory or filename stem. That misfires when a repo's test doesn't mirror the source path, even though a real-DB test covers the change.

This teaches the gate to prefer capture over the guess: when the run captured new query surface, a real-DB test demonstrably executed the change against Postgres, so the flag is dropped.

Why

Capture is ground truth for the exact blind spot this gate exists to catch: a query that runs against Postgres in no test produces no captured query. If QD captured new queries, the diff heuristic's "no related test" conclusion is contradicted by observed execution.

Concrete case — Nutcracker #749

• The PR adds findByUser to src/db/postgres.ts and a real-DB test in tests/pg/postgres.test.ts.
• The gate fired "no related data-layer test": tests/**pg**/postgres.test.ts doesn't share a directory or stem with src/**db**/postgres.ts, so isRelated missed it.
• Meanwhile QD captured 2 new queries in the same run (the LIMIT 50 shape — straight from the test's findByUser(u, 50), not the route's 100/500) and listed them in the very same comment that claimed nothing exercises them.

With this change, newQueryHashes.length > 0 → the verdict is null → the warning never posts.

How

• evaluateTestPresence(files, config, capture?) gains an optional capture with newQueryHashes. Non-empty → return null.
• main.ts feeds comparison.newQueries hashes into the gate (already computed before the gate runs).

Limitation (next rung, #3503)

Suppression is run-level: a PR that tests file A but ships an untested query in file B is fully cleared for now. Per-query→file attribution is #3503. This errs on the under-fire side the gate already favours (warn-only).

Tests

• New: capture with new-query hashes clears the flag (the #749 shape); empty capture still flags. Full gate suite green (24), typecheck clean.

[github-actions]

Query Doctor Analysis

3 queries analyzed

0 regressed · 0 improved · 0 new · 0 removed

2 pre-existing issues

• SELECT "guests"."id", "guests"."session_id", "guests"."username", "guests"."avatar_path", "guests"."color", "guests"."side", "guests"."audio_recording_path", "guests"."audio_recording_public", "gue...
  index assets(event_id, inserted_at desc)
  cost 31,003,449 → 1,498 (100% reduction)
• SELECT * FROM guest_ip_addresses WHERE ip_address = '127.0.0.1';
  index guest_ip_addresses(ip_address)
  cost 154,402 → 8 (100% reduction)

_{Using assumed statistics (10000000 rows/table). For better results, sync production stats.}

_{More detail → get_ci_run({ runId: "019f5dae-9758-7db3-a665-631f897d95c1" }) · view run · docs}