Database commits halved for task dequeues

Summary

Nests the TaskRunExecutionSnapshot creation inside the taskRun.update() Prisma call in the dequeue flow, reducing 2 DB commits → 1 per dequeue operation. This is the highest-volume of the five unmerged flows identified in TRI-8450 (~9,200 commits/sec on the engine service).

Pattern: Follows the same nested-write approach already used in the completion path (runAttemptSystem.ts:735) and trigger path (engine/index.ts:674).

Changes:

• dequeueSystem.ts: Moved snapshot creation into executionSnapshots: { create: {...} } within the existing taskRun.update(). Pre-generates the snapshot ID via generateInternalId() (plain cuid, matching what Prisma's @default(cuid()) produces) so the event emission, heartbeat enqueue, and return value can all be constructed from data already in scope — no extra DB read needed after the merged write. SnapshotId.toFriendlyId() is used only for the return value's friendlyId field, matching the original createExecutionSnapshot behavior.
• executionSnapshotSystem.ts: Added public enqueueHeartbeatIfNeeded() method that exposes the heartbeat scheduling logic (previously only available internally via createExecutionSnapshot). This is needed because PENDING_EXECUTING requires a heartbeat, unlike the FINISHED status in the completion reference pattern. This method is reusable by future merge targets (retry-immediate, checkpoint, cancel, requeue).

Net DB change per dequeue: eliminates 1 write transaction (the separate TaskRunExecutionSnapshot.create). No extra reads added — the snapshot ID is pre-generated and the executionSnapshotCreated event payload is constructed inline from values already available in the closure.

Review & Testing Checklist for Human

• Verify manually-constructed event payload matches DB state: The executionSnapshotCreated event is now built inline (not read back from DB). Confirm the field values (runStatus: "PENDING", attemptNumber, checkpointId, workerId, runnerId, completedWaitpointIds) match what Prisma actually writes. A mismatch here would be silent — event consumers would get stale/wrong data.
• Verify attemptNumber source is equivalent: Old code used lockedTaskRun.attemptNumber (post-update result). New code uses result.run.attemptNumber (pre-update). The taskRun.update() data payload does NOT include attemptNumber, so they should be identical — but confirm this assumption holds for all dequeue scenarios (e.g. retried runs).
• Verify isValid defaults to true in schema: The old createExecutionSnapshot explicitly set isValid: error ? false : true. The nested create omits isValid (no error in the dequeue happy path). Confirm the Prisma schema default for TaskRunExecutionSnapshot.isValid is true.
• Verify runStatus: "PENDING" hardcoding matches the mapping: The old code passed lockedTaskRun.status ("DEQUEUED") to createExecutionSnapshot, which mapped it to "PENDING" via run.status === "DEQUEUED" ? "PENDING" : run.status. The new code hardcodes "PENDING" directly. This is correct but brittle if status ever changes from "DEQUEUED" to something else upstream.
• Spot-check completedWaitpoints connect + order logic: The nested create replicates the connect/order logic from createExecutionSnapshot (lines 387-393). Verify the snapshot.completedWaitpoints type provides id and index fields compatible with this usage.
• Verify checkpoint in return value: The return now uses snapshot.checkpoint (from the previous snapshot) instead of reading the newly-created snapshot's checkpoint relation. Since checkpointId is passed through unchanged, they should be identical — but worth a sanity check.

Recommended test plan: deploy to staging, run the sample_pg_activity.py sampler for a 5-minute window, and verify the COMMIT count drop on the engine service + proportional IO:XactSync reduction.

Notes

• This only covers the dequeue flow (flow #1 from TRI-8450). The remaining four flows (retry-immediate, checkpoint, requeue, cancel) are separate follow-ups.
• The new enqueueHeartbeatIfNeeded method is deliberately designed for reuse by those follow-up PRs.
• CI note: the priority.test.ts failure in shard 7 is a flaky ordering assertion unrelated to this change (it compares friendlyId values in dequeue order). The audit check is also pre-existing/unrelated.

Link to Devin session: https://app.devin.ai/sessions/034fe0e7224f49278a2de260203e1377 Requested by: @ericallam