By: Tom Sydney Kerckhove <syd@cs-syd.eu>
Mutation: control-group (no-op) mutations expected to survive A control is a deliberate no-op: the plugin wraps an expression as `(\ctrl -> ifMutation cmid ctrl ctrl) e` — the same expression on both branches, a genuine non-diff — every `controlInterval` (12) real mutations. Both branches share the subtree via the lambda binder so the no-op does not duplicate (and blow up) the instrumented expression. A control changes no behaviour, so it is expected to survive. A killed control means the mutation testing itself is unsound (a flaky/nondeterministic suite or a harness bug), not a real kill, so it is reported separately as a warning and excluded from the killed/survived score and the exit code. Marked via the reserved operator name "Control" (no new record field). New MutationOutcome variants OutcomeControlPassed/OutcomeControlFailed and MutationResult variants MutationControlPassed/MutationControlFailed; the driver remaps a control's exit-code classification accordingly. isMutationFailure is False for both so a surviving control never trips fail-fast. Regenerated the example manifest goldens (control entries only).
| Time to Start | Worker time | Duration | Time to finish | Idle | |
| Config | 0s | 2s | 2s | 2s | 0s |
| Eval | 2s | 43s | 43s | 45s | 0s |
| Build | 5s | 2m08s | 45s | 51s | 0s |
| Suite | 0s | 2m54s | 51s | 51s | 0s |