---
id: mem-engine-scheduler-outbox
name: Mem engine — scheduler (`schedule`/`unschedule`/`run_schedules`) and outbox helper
status: completed
depends_on: [mem-engine-queues, mem-engine-locks]
scope: moderate
risk: medium
impact: component
level: implementation
tags: [wave-6, mem-engine, scheduler, outbox]
---

## Description

The collapsed scheduler and the outbox helper
([ADR-009](../architecture/decisions/009-scheduler-collapse.md),
[ADR-014](../architecture/decisions/014-outbox-tx-enqueue.md)):

- **Scheduler surface**: `schedule(name, spec, queue, payload, opts)`
  (upsert by name; *both* name-bearing arguments validated — schedule
  name and queue argument identically, `InvalidName`/`ReservedName`),
  `unschedule(name) -> bool`, and the opt-in
  `run_schedules(stop: StopToken)` runner over a mem-owned tick task.
- **Tick machinery — engine-uniform** ([ADR-009](../architecture/decisions/009-scheduler-collapse.md)
  §4's rule; single-instance leadership is trivially owned but the
  machinery still runs): each boundary fire enqueues ordinary work
  stamped with the schedule's `ScheduleOpts` resolved over the target
  queue's derived engine defaults; fire+advance is atomic under the
  guarded state (the no-double-fire floor); **bounded catch-up with
  the fixed 64-boundary cap and skip-forward past the cap**
  (mem-owned tick implementation — third owner per
  [ADR-012](../architecture/decisions/012-forked-substrate-design.md)
  §2); leadership rides the reserved `__alkstore_scheduler` lock
  through the lock mechanism (so two runners on one instance contend
  through the same machinery the other engines use; loss →
  `Err(LeadershipLost)`, clean stop → `Ok(())`).
- **Spec grammar v1**: `@every <n><unit>` (`s|m|h|d`) only — mem owns
  its parser (third copy, the grammar is small and pinned); cron
  strings rejected (`InvalidSpec`). Boundary waits ride tokio time.
- **Outbox helper**: `Outbox { enqueue, run_once }` per
  [ADR-019](../architecture/decisions/019-mechanism-handle-surfaces.md)
  §5 — `run_once(worker_id, delivery) -> bool` is pull: claim one,
  ack on `Ok`, `retry(err, None)` on `Err`; **no engine-issued
  heartbeat inside delivery** (inherited posture);
  `outbox_enqueue_tx` staged in the overlay by `mem-engine-seam-tx`
  (the 60/5/5 stamp set); the derived backing queue
  `__alkstore_outbox:{outbox}` unreachable by `enqueue_tx`
  (validation already pins the reserved prefix), name format pinned
  identical to the other engines (the suite's derived-queue-naming
  row composes it).

Unit tests pin: boundary fires (deterministic, tokio-time driven),
bounded catch-up + skip-forward, leadership lock contention/loss
through two `run_schedules` calls, outbox run_once ack/retry shapes,
derived-name format.

## Acceptance Criteria

- [x] Scheduler surface + tick: boundary fire, catch-up (≤64),
      skip-forward — unit-pinned with tokio-time determinism
- [x] Leadership contention through the `__alkstore_scheduler` lock;
      `LeadershipLost` on loss, `Ok(())` on clean stop — pinned
- [x] Schedule name + queue argument validation; `@every`-only parser
      (cron → `InvalidSpec`) — pinned
- [x] Outbox: `enqueue`/`run_once` semantics (no engine heartbeat);
      derived backing-queue name format identical to both engines —
      pinned
- [x] `cargo check --target wasm32-unknown-unknown -p alkstore-mem`
      clean; workspace gates green

## References

- docs/architecture/queues.md; core-contract.md §scheduler, §outbox
- docs/architecture/decisions/009-scheduler-collapse.md §1/§3/§4/§6;
  014-outbox-tx-enqueue.md; 019 §4/§5; 020 §3
- docs/architecture/engine-mem.md §Mapping the contract
  (scheduler/outbox row)
- tasks/pg-engine-scheduler-outbox.md (the structural twin's task of
  record — tick/catch-up/leadership shapes)

## Notes

> Filled by implementation agent, 2026-10-10.

1. **The implementation already landed in the seam task** — the same
   all-or-nothing trait-impl disposition the previous wave-6 mechanism
   tasks recorded: the scheduler (`scheduler.rs`'s register table,
   `run_tick`, the runner) and the outbox helper (`outbox.rs`) were
   implemented with the seam's whole-engine scope; this task found its
   mechanisms *implemented*.
2. **Coverage reconciliation**: already pinned by the seam suite —
   the boundary-fire row (deterministic `run_tick` fires, ready-at-
   fire-instant rows stamped with the registered values + plain
   defaults, no-double-fire floor, fire+advance as one guarded op),
   the bounded-catch-up row (600 s behind → exactly 64 fires, never
   300; skip-forward lands the next boundary strictly future with the
   grid honest; never-due schedules untouched), the leadership rows
   (two contenders through the `__alkstore_scheduler` lock: one wins,
   the loser `Err(LeadershipLost)`; a blocked lock loses before any
   fire; clean stop → `Ok(())` and the lease released for the next
   runner), the register rows (upsert-by-name + stamp resolution +
   read-back; both name-bearing arguments validated + cron rejected
   pre-storage with nothing written; the `@every` grammar matrix),
   `unschedule` (removal + absent-false + reserved-name rejection),
   `fired_rows_are_ordinary_queue_work` (the fire claims through the
   ordinary queue), the outbox rows (Ok ⇒ ack / Err ⇒ retry with the
   queue's equal-jitter curve and the delivery error riding the
   exhaust path onto the dead row; the derived 60/5/5 stamps with
   `max_attempts` the one override; no-work `Ok(false)`; empty
   `worker_id` rejected), and the derived backing-queue name format +
   `enqueue_tx` unreachability.
3. **What this task added** — the one unpinned posture from the
   description: `run_once_issues_no_engine_heartbeat_in_delivery` —
   the handover carries the raw claim deadline (no engine-side
   renewal before or inside delivery), and the boxed
   [`JobHandle`]'s own `heartbeat` remains available to the closure
   (renewal is the consumer's obligation, ADR-019 §5). The delivery
   fixture grew `handover_deadline` + a manual-heartbeat arm for it.
4. **No production code changed** — verified correct as-found; tests
   only (+1 in `outbox.rs`, fixture widened, 100 mem tests total).
   The scheduler's boundary waits ride realtime tokio time with
   stamps on the engine clock; the tick/catch-up/leadership pins
   drive the crate-internal `run_tick`/`run_schedules` directly, so
   determinism holds without realtime waits.

## Summary

> Filled on completion, 2026-10-10.

Completed the mem engine's scheduler/outbox task against the seam
task's foundation: reconciled the description's pin list against
`alkstore-mem/src/scheduler.rs` + `outbox.rs`'s existing suite (14
pre-existing tests), found every tick/catch-up/leadership/validation/
outbox shape already pinned, and added the one gap — the
no-engine-issued-heartbeat posture pinned end-to-end (raw claim
deadline at handover; the closure's own heartbeat path available and
honored). Acceptance criteria: scheduler surface + tick determinism ✓
(seam rows), leadership ✓ (seam rows), validation + grammar ✓ (seam
rows), outbox semantics + derived name format ✓ (seam rows + the new
heartbeat row), gates ✓. Verified: `cargo test -p alkstore-mem`
100/100 (99 + 1 new, new test green solo), workspace `cargo test`
green, `cargo clippy --all-targets -- -D warnings` clean,
`cargo fmt --check` clean, `cargo check --target
wasm32-unknown-unknown -p alkstore-mem` clean.