[lucasbraum]

The SDK pre-run estimate charged a full uncached token allowance for every site even though one session shares rule knowledge. On alanagoyal this predicted $1.08 for 18 sites and spent $0.1336, forcing an unnecessary budget increase.

Estimate SDK sessions from distinct migration rules, a small per-site context allowance, and a session minimum, with an explicit 1.5× safety margin applied before rounding to cents. Keep declaration-only anchors in the site allowance without charging another independent rule. The patch executor's estimate and both executors' hard budget checks remain unchanged.

Recorded run	Before	Actual	After	After / actual
alanagoyal, React 18 → 19	$1.08	$0.1336105	$0.23	1.72×
calmcp, pilot round 4	$0.30	$0.0842459	$0.14	1.66×
dms-saas, pilot round 4	$0.60	$0.2740438	$0.42	1.53×
enki, pilot round 4	$0.54	$0.1431526	$0.29	2.03×

The original reports and bench metadata agree. #169's round 5 reuses round 4's Uptide runs, so it is not counted again. Mechanical sites were already correctly excluded. The old token allowance implicitly covered retries; it had no explicit feedback multiplier. These runs used zero or one feedback round, not three.

Recorded fixtures and docs/cost-estimate-calibration.md document the evidence, formula, and limits. This is a four-run in-sample calibration, not a guarantee on unseen migrations. The safety margin reduces the risk of turning a free preflight stop into a paid mid-run budget stop. Recorded-pair tests require estimates between 1.3× and 2.5× actual spend. No paid runs were made. Install caching is outside this PR's scope.

UPT-14/UPT-111 behavior is preserved: preflight rejects estimates above the limit, equality is allowed, Action/App runs work within the original limit, feedback spends only the remainder, and flake reruns and per-call reservations are unchanged. Tests cover recorded pairs, mechanical exclusion, anchors, model pricing, and SDK preflight/runtime budget boundaries.

Validation passed: pnpm lint (existing Biome schema notice and fixture warning), pnpm typecheck, and the estimator and generic fix tests. Tests also verify that the margin is applied before cent rounding.

Refs UPT-94 (cost-estimate part only).

[lucasbraum]

@tenki-reviewer

[tenki-reviewer]

Review complete. No blocking issues — approved ✅; 1 nitpick below.

🧹 Nitpicks (1) — 🟢 1 low

• 🟢 Doc's calmcp rule count contradicts the fixture (cost-estimate-calibration.md:16) — The doc records 1 distinct rule and a $0.14 estimate for calmcp (docs/cost-estimate-calibration.md:16, :67), but the fixture's calmcp TS2740 site has no rule field, so sdkCostEstimate falls back to the change path and counts 2 rules (packages/core/src/llm/__fixtures__/cost-runs.json:270), yielding $0.15 and a ratio of ~1.78 instead of the documented 1.66.

---

This PR introduces a pre-run LLM cost estimator for sdk agent runs in packages/core/src/llm/fixer.ts, combining a session floor with per-rule and per-site allowances multiplied by a 1.5× margin, and wires it into fix/run.ts so the estimate is checked against configured spending limits before any agent spend. Calibration is grounded in a new recorded-runs fixture, with docs explaining the derivation and tests asserting estimates stay within a 1.3×–2.5× band of actuals; configured limits are unchanged. One small documentation inconsistency remains around the calmcp rule count (see inline comment).

Files	Change
packages/core/src/llm/fixer.ts	Adds sdkCostEstimate with session floor, per-rule/per-site allowances, and 1.5× margin.
packages/core/src/fix/run.ts	Selects the SDK estimate for sdk agent runs and gates preflight against spending limits.
packages/core/src/llm/__fixtures__/cost-runs.json	Adds recorded calibration runs used as the estimator's ground truth.
packages/core/src/llm/cost-estimate.test.ts, packages/core/src/fix/generic.test.ts	New tests covering estimate calibration band and gating behavior.
docs/cost-estimate-calibration.md, .changeset/quiet-rules-estimate.md	Documents the calibration methodology and adds a changeset.

_{Reviewed commit: cd84e4f}