Review round (#86412):
- the except-import fallback returned the RAW oversized value, re-opening
the exact macOS time_t overflow this fix prevents; it now fails closed
to a finite ~1-year cap matching agent.deadline.MAX_SAFE_TIMEOUT_S
- clamp engagement logs a WARNING so operators see the semantic change
- new tests: float-form oversized value (YAML 1e18), warning emission,
and the import-failure fail-closed path (blocked-import probe proving
the result stays Lock.acquire-safe)
kshitijk4poor