Rationale
The task record still describes this checkout — same branch, and HEAD at or ahead of the recorded commit.
Required behaviour
A task record is trusted only while it still describes this checkout: same branch, HEAD at or ahead of the recorded commit.
Failure behaviour
A violation is a FAIL finding under the category state, and the command that found it exits 10. Under watch the same violation is reported as drift and the command exits 11.
Verification
mj_validate_state decides it, dispatched from check, finish, watch. The behavioural case test/cases/04_start_check.sh proves it, and CI runs that case.