test: mutation-harden gas/index unit coverage

[thedavidmeister]

Summary

Mutation-hardens the GasManager unit suite (src/gas/index.ts). A
scoped adversarial-mutation pass over the gas-estimation peripheral logic
found 10 surviving mutants in the existing src/gas/index.test.ts suite —
all in the constructor default-value logic, the onTransactionMine
threshold/deadline arithmetic, and the watchGasPrice idempotency guard.

This PR adds 6 discriminating tests (tests-only; no src/ change) that
each pass on the clean baseline and fail under the corresponding mutation.
Every previously-surviving mutant is now killed.

Mutation matrix

#	Source line	Mutation	Before	After
M1	maxGasPriceMultiplier = baseGasPriceMultiplier + 50	+ 50 → - 50	SURVIVED	KILLED
M2	if (config.txTimeThreshold !== undefined)	guard → false	SURVIVED	KILLED
M3	if (config.gasIncreasePointsPerStep !== undefined)	guard → false	SURVIVED	KILLED
M4	if (config.gasIncreaseStepTime !== undefined)	guard → false	SURVIVED	KILLED
M13	gasIncreasePointsPerStep: number = 3	3 → 7	SURVIVED	KILLED
M14	txTimeThreshold: number = 30_000	30_000 → 1	SURVIVED	KILLED
M15	gasIncreaseStepTime: number = 60 * 60 * 1000	→ 1	SURVIVED	KILLED
M5	if (txMineRecord.length >= this.txTimeThreshold)	>= → >	SURVIVED	KILLED
M6	this.deadline = Date.now() + this.gasIncreaseStepTime	+ → -	SURVIVED	KILLED
M9	if (this.isWatchingGasPrice) return;	guard → false	SURVIVED	KILLED

Already-covered (audited, no new test)

• Math.min(max, multiplier + step) clamp → Math.max — KILLED by existing
  "should not increase the multiplier over the max value".
• >= → <= on the deadline-reset comparison — KILLED by existing
  "under threshold and reset" (past deadline).
• isOk() branches in init/watchGasPrice — covered by existing
  init/interval tests.

Equivalent (intentionally not tested)

• if (this.deadline && Date.now() >= this.deadline) — dropping the
  this.deadline && short-circuit is equivalent in practice: deadline is
  only ever undefined or a positive timestamp, and Date.now() >= undefined
  is already false, so no reachable state distinguishes the mutant.
• >= vs > on the deadline comparison would only be discriminated by
  Date.now() === deadline exactly, which is non-deterministic.

New tests added (src/gas/index.test.ts, +94 lines)

• should not start a second watcher when already watching (M9)
• should apply class defaults when optional config fields are omitted (M1/M2/M3/M4/M13/M14/M15)
• should use provided optional config values over the defaults (assignment branches)
• should increase the multiplier when mine time equals the threshold exactly (M5)
• should set the deadline to now plus the step time when increasing (M6)
• should not reset the multiplier when the deadline is still in the future (future-deadline guard)

Gaps checklist

• Constructor optional-field default branches
• Class-field default values (points / step time / threshold)
• maxGasPriceMultiplier = base + 50 fallback
• onTransactionMine >= threshold boundary
• Deadline + stepTime arithmetic
• Future-deadline no-reset path
• watchGasPrice double-start idempotency
• init/watchGasPrice isErr branches — already covered by existing tests (audited)

Verification

• tsc -p ./tsconfig.check.json clean
• eslint ./src/gas/index.test.ts clean
• Full vitest unit suite green: 847 tests passed (59 files + logger)
• git diff src/ is empty — tests-only change
• The e2e fork test jobs are a pre-existing environmental red (RPC/secrets) and are untouched by this PR.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

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Run ID: 2a8de2d7-f2bc-4424-9227-315c33ace998

📥 Commits

Reviewing files that changed from the base of the PR and between 3da315d and c9acc0a.

📒 Files selected for processing (1)

• src/gas/index.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 2026-06-15-solver-config-coverage

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