[systemfsoftware-maker]

Summary

Three planMutantTests property laws no longer fail at random. They failed because their generators built Mutant values that the Mutant schema refuses.

Cause

#273 added a struct filter to Mutant (Mutant.schema.ts:144-147): a Subsumed mutant must be Ignored, and a Readmitted mutant must not be. orderedCommandArb and staticKillerCommandArb cleared status but kept the subsumption they drew. Whenever that draw was Subsumed, Mutant.Mutant.make threw before the law ran any step (Schema validation failed, "Failing step: no step ran").

Laws that failed this way:

• ∀o_OrderedCoveringTests_≡ThePreviousKillerLeadsThenAscendingDryRunTime (orderedCommandArb)
• ∀r_CoveredRun_≡NeverPublishesKillerTestIds (orderedCommandArb)
• ∀s_StaticPriorKiller_≡TheRunPublishesItsKnownKillerTestIdsInTheirOrder (staticKillerCommandArb)

Fix

lawfulSubsumptionOf(mutant, status) keeps a drawn subsumption only if it is valid for the status the generator sets. The check is Mutant.subsumptionMatchesStatus, the same predicate the struct filter uses. With no status, only Subsumed draws are dropped. With Ignored, only Readmitted draws are dropped. All three generators use the helper; coverageCommandArb already did this inline. The struct filter, every law's assertions and the run counts are unchanged.

Runs of plan-mutant-tests.workflow.property.test.ts

Tree	Runs	Passed	Failed
main at 3cb134232, before the fix	60	56	4
this branch at 9a4db283b	60	60	0
this branch merged with main at 815754693	30	30	0

On the merged head, pnpm typecheck, oxlint on the changed file, dprint check and gritlint check pass. The changeset is none because no shipped code changes.

Follow-up

• statusReason gap (pre-existing, on main since cfde427d1). coverageCommandArb always sets the input statusReason to undefined, so ∀r_IgnoredEarlyResult_≡ItsReasonIsForwardedOrNamesARule can't catch a planner that drops a closed mutant's real reason. The generator should draw a valid reason when the mutant is closed. That is out of scope here.

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

[ryanleecode]

Verified at 915911f: up to date with main ce66cd7; check, all 5 e2e legs, checker-parity and Nix green; 0 open threads. Test-only (one property-test generator + changeset 'none'): generators clear subsumption when they clear status, matching Mutant.subsumptionMatchesStatus; the same invalid-draw cause #303 independently measured (5-15 of 2000 draws). Only red: bench typescript-checker leg, failing on every PR until bench leaves the PR path.