`testing.mutation-claims-are-executed` was amended on main while this branch was in review (#881,
merged as #914): a sentence asserting that a specific mutation reddens — or does not redden — a named
test is now either a `CLAIMS` entry in `scripts/tests/mutation_manifest.py` that executes every run,
or it is not written. This branch carried six such sentences and none of them can be declared:
`Claim.node_id` resolves a proof to `scripts/tests/<node id>` and `run_pytest` invokes pytest, so an
NUnit proof has no representation in that harness at all.
Durable prose now states the mechanism each test is built on — which serializer difference, which
engine branch — which a reader re-checks by reading the code rather than by trusting a remembered
outcome. The record says that in one paragraph, so the limit is stated rather than papered over.
The outcomes themselves are here. Re-measured 2026-09-05 on this branch's tree (the commit before
this one), each mutant applied to the working tree and restored from the index between runs, tree
verified clean afterwards:
positive control ScriptedScheduleControllerTests Passed: 9, Failed: 0
OpenApiSerializerContractTests Passed: 4, Failed: 0
Bind<T> -> System.Text.Json with JsonSerializerDefaults.Web
Failed: 2, Passed: 7 — Production_Body_Binder_Ignores_Required_Members,
Production_Body_Binder_Keeps_Declared_Defaults_Over_An_Explicit_Null
BodyBinderSettings = ApiJsonSettings.Create() -> new JsonSerializerSettings()
Failed: 1, Passed: 8 —
Production_Body_Binder_Keeps_Declared_Defaults_Over_An_Explicit_Null
OpenApiSerializerContractTests RuntimeSettings -> new JsonSerializerSettings()
Failed: 4, Passed: 0 — all four cases, on PascalCase keys
ScriptedScheduleController AddDuration(..., request.Trim, ...) -> false
Failed: 1, Passed: 8 — Committed_Script_Fixture_Produces_The_Pinned_Snapshot
ScriptedScheduleController PadUntilExact(..., request.Trim, ...) -> false
Failed: 1, Passed: 8 — Committed_Script_Fixture_Produces_The_Pinned_Snapshot
The last one is the round-two finding closed and re-witnessed: before the fixture's pad target moved
off the content boundary, that mutant left all nine green.
A squash merge writes its own message, so these figures also belong in the PR description.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015QqCpYFsKgnAnx6jVwrKiV
timothyandClaude Fable 5.1
3df98d247f