Task 8 of 10 complete. Exposes read-only scheduler health data including:
- Queue depth and distribution by instance type
- Dead-letter queue inspection (top 25 tasks with error details)
- Circuit breaker states (instance-level)
- Staleness scores per instance
New API endpoint:
GET /api/monitoring/scheduler/health (requires authentication)
New snapshot methods:
- StalenessTracker.Snapshot() - exports all staleness data
- TaskQueue.Snapshot() - queue depth & per-type distribution
- TaskQueue.PeekAll() - dead-letter task inspection
- circuitBreaker.State() - exports state, failures, retryAt
- Monitor.SchedulerHealth() - aggregates all health data
Documentation updated with API spec, field descriptions, and usage examples.
Replaces immediate polling with queue-based scheduling:
- TaskQueue with min-heap (container/heap) for NextRun-ordered execution
- Worker goroutines that block on WaitNext() until tasks are due
- Tasks only execute when NextRun <= now, respecting adaptive intervals
- Automatic rescheduling after execution via scheduler.BuildPlan
- Queue depth tracking for backpressure-aware interval adjustments
- Upsert semantics for updating scheduled tasks without duplicates
Task 6 of 10 complete (60%). Ready for error/backoff policies.
