# Scheduler Queue — Sprint 16 Coordination Notes

Queue work now has concrete contracts from `StellaOps.Scheduler.Models`:

* Planner inputs reference `Schedule` and `ImpactSet` samples (`samples/api/scheduler/`).
* Runner segment payloads should carry `runId`, `scheduleId?`, `tenantId`, and the impacted digest list (mirrors `Run.Deltas`).
* Notify fanout relies on the `DeltaSummary` shape already emitted by the model layer.

## Action items for SCHED-QUEUE-16-401..403

1. Reference `StellaOps.Scheduler.Models` so adapters can serialise `Run`/`DeltaSummary` without bespoke DTOs.
2. Use the canonical serializer for queue messages to keep ordering consistent with API payloads.
3. Coverage: add fixture-driven tests that enqueue the sample payloads, then dequeue and re-serialise to verify byte-for-byte stability.
4. Expose queue depth/lease metrics with the identifiers provided by the models (`Run.Id`, `Schedule.Id`).

## JetStream failover notes

- `SchedulerQueueOptions.Kind = "nats"` will spin up `NatsSchedulerPlannerQueue` / `NatsSchedulerRunnerQueue` instances backed by JetStream.
- `SchedulerQueueHealthCheck` pings both planner and runner transports; register via `AddSchedulerQueueHealthCheck()` to surface in `/healthz`.
- Planner defaults:
  ```yaml
  scheduler:
    queue:
      kind: nats
      deadLetterEnabled: true
      nats:
        url: "nats://nats:4222"
        planner:
          stream: SCHEDULER_PLANNER
          subject: scheduler.planner
          durableConsumer: scheduler-planners
          deadLetterStream: SCHEDULER_PLANNER_DEAD
          deadLetterSubject: scheduler.planner.dead
        runner:
          stream: SCHEDULER_RUNNER
          subject: scheduler.runner
          durableConsumer: scheduler-runners
      redis:
        deadLetterStream: scheduler:planner:dead
        idempotencyKeyPrefix: scheduler:planner:idemp:
  ```
- Retry / dead-letter semantics mirror the Redis adapter: attempts beyond `MaxDeliveryAttempts` are shipped to the configured dead-letter stream with headers describing `runId`, `scheduleId`, and failure reasons. Set `deadLetterEnabled: false` to drop exhausted messages instead.
- Depth metrics surface through `scheduler_queue_depth{transport,queue}`; both transports publish lightweight counters to drive alerting dashboards.

These notes unblock the queue guild now that SCHED-MODELS-16-102 is complete.