Prioritize selected checks before optional deadline-bound work

When a monitoring worker has a hard completion deadline, filtering which results count as successful does not reserve execution time for those checks. Run the selected availability checks before optional diagnostics, bound each phase, and reserve export and teardown time. Otherwise earlier optional work can consume the remaining budget and manufacture monitoring gaps across healthy components. Record phase timing and unknown outcomes so incomplete coverage remains visible. Reordering cannot recover a slot whose deadline has already passed, and code-level starvation risk does not prove the cause of a particular production gap.

Applies when: Scheduled monitoring mixes selected availability checks and optional diagnostics under a shared deadline. Keywords: monitoring deadline optional diagnostics selected checks budget starvation coverage