Two veto layers in reconcile(), worker.py untouched:
- Global live-coordinator veto: a running task whose
coordinator_parts parse (via cloud.coordinator.parse_parts)
to a non-empty list and whose last_heartbeat is within
120s blocks all scale-down this round; low_streak is
frozen, not reset, so scale-down resumes on the next
low-depth round once the veto lifts.
- Per-victim busy veto: a LIFO victim whose workers row
is alive with running>0 is skipped, but only when the
DB also has a live running task (ghost registry rows
with no live DB task do not block).
- Coordinator-veto query failure fails closed (no stop,
guard error recorded); victim-veto read failure fails
open for that layer only.
- A missing/stale workers row is treated as idle.
Tests: 7 new ScaleDownGuardTestCase cases (live/stale
coordinator, non-coordinator, invalid parts, busy/idle
victims, ghost registry, streak freeze); cloud suite
1077 tests OK (4 skipped).