Approve runner cleanup idempotence after independent lifecycle checks

Changes: Accept the bounded S00-014 cleanup correction and record independent QA evidence and handoff; no reviewer source changes.
Validation: Four focused signal/descendant tests and make check passed (72 tests); prior function independently fails the injected repeated-signal regression in memory. Inspected executor patch/message and scope; git diff --check passed. Natural EPERM, Windows and parent-task acceptance are not claimed.
