fix(review): gate the tuning advisor on wouldMerge and weighted precision, matching the breaker - #10142

What & why

src/review/auto-tune.ts has two consumers of the same GateEvalReport: the circuit breaker (planAutoTune) and the tuning advisor (computeTuningRecommendations, whose output feeds the auto-apply/override path). They disagreed on both rules the breaker documents.

1. Sample gate: decided vs wouldMerge. The advisor gated on r.decided < MIN_DECIDED; decided counts every prediction with a known outcome, holds included. So the exact shape planAutoTune's comment names — 9 holds + 1 wrong would-merge — clears decided >= 10, produces mergePrecision === 0, and emits a warn carrying an overridePayload. That payload is auto-applicable: runAutoApplyRecommendations queues a live confidence-floor raise off a single prediction the breaker already refuses as statistically meaningless.

2. Precision field: raw vs weighted. GateEvalRow's doc states the breaker gates on the reversal-discounted weighted* fields "so a high volume of later-reverted merges cannot keep the raw number artificially healthy while gaming the breaker into staying disengaged." The advisor read the raw mergePrecision/closePrecision/closeFalse. REVERSAL_DISCOUNT_WEIGHT is 0, so a project whose merges are systematically reverted has weightedMergePrecision ≈ 0 while mergePrecision stays healthy — the breaker engages, the advisor stays silent, and no tightening is recommended for exactly the project that needs one. Worse: evaluateShadowPromotion's recovery check was fed the raw number, so a project held by the reversal-weighted breaker had its pending tightening dropped on a figure the breaker itself distrusts.

3. Dead guard arm. planCloseAutoTune's guard was r.wouldClose < AUTOTUNE_MIN_DECIDED || r.weightedClosePrecision == null — but weightedClosePrecision is non-null iff wouldClose > 0, so once wouldClose >= 10 the == null disjunct was unreachable (a dead branch under branch-counted coverage).

The fix

• computeTuningRecommendations's sample gate is r.wouldMerge < MIN_DECIDED (message names the would-merge count); its merge-risk and ready tests read r.weightedMergePrecision; its close-side warn reads r.weightedClosePrecision against AUTOTUNE_CLOSE_PRECISION_FLOOR (closeFalse stays in the message text, no longer the condition).
• AutoApplyContext.mergePrecision is renamed to weightedMergePrecision and threaded into evaluateShadowPromotion's currentMergePrecision, so the recovery check reads the weighted number.
• planCloseAutoTune's guard is reordered to null-check first (mirroring planAutoTune), making the null arm reachable.

Unchanged: every threshold constant (MIN_DECIDED 10, RISK_MERGE_PRECISION 0.9, READY_MERGE_PRECISION 0.95, READY_CLOSE_PRECISION 0.9, AUTOTUNE_CLOSE_PRECISION_FLOOR 0.85, TIGHTEN_FLOOR_TARGET), the warn/good/info ordering, the TuningRec/OverridePayload shapes, isStrictlyTightening's tightening-only direction, and planAutoTune/applyAutoTune/shouldAutoClear and their close twins.

Tests (test/unit/auto-tune.test.ts, test/unit/auto-apply.test.ts)

• REGRESSION: 9 holds + 1 wrong would-merge (decided: 10, wouldMerge: 1) is info-only with no overridePayload; a healthy raw merge precision (0.98) with a failing weighted one (0.2) warns with overridePayload: { confidenceFloor: 0.95 }.
• planCloseAutoTune's reordered null arm is reachable (weightedClosePrecision: null, wouldClose: 20 → no action).
• The two existing tests that encoded the old raw-field/closeFalse behaviour are updated to the weighted-gate contract; the shadow-promotion recovery tests now pass weightedMergePrecision.
• All new assertions fail on main.

Validation

• Diff coverage on both src/review/auto-tune.ts and src/review/auto-apply.ts is 100% line and branch.
• npm run typecheck clean for these files (the rename is caught end-to-end — the sole call site, selftune-wire.ts, does not pass the field, and the test call sites are updated); npm run engine-parity:drift-check passes (neither file is a twin); npm run dead-exports:check clean; both suites (158 tests) green.
• git diff --check clean; no schema/migration/generated-artifact change.

Closes #10014