Module: utils/runAbortChannel

CAP-002 Phase 2 (Prerequisite #5) — cross-process run-abort signal channel over Redis pub/sub.

Why this exists: when a user clicks "Abort" on a sharded run, the abort route in backend/src/routes/runs.js only knows about the local replica's workerAbortControllers. Shard workers running on other replicas would keep executing until natural completion, leaving orphan jobs and burning compute. This module fans the abort signal out to every replica so each one can cancel any matching in-flight job via its local workerAbortControllers map.

Channel contract

sentri:run-abort — JSON-encoded { runId: string, origin: string }. Published by the abort route; subscribed by every shard worker at boot.

Self-echo suppression

Each Node process generates a fresh origin id at module load (UUID-shape hex string, same pattern as routes/sse.js:_instanceId). The publisher stamps it on every message; the subscriber drops messages whose origin matches its own. This prevents the same-process round-trip — the local fast-path in routes/runs.js already aborted the controller before publishing, so re-firing it via the channel would be wasteful (and could race against the cleanup that the route performed synchronously).

Degraded mode (no Redis)

When REDIS_URL is unset or isRedisAvailable() returns false:

• publishRunAbort() returns false and is a clean no-op.
• subscribeToRunAborts() returns false; the worker keeps its in-process workerAbortControllers map as the only abort path.

Single-replica deployments therefore behave bit-for-bit identically to pre-Phase-2 today — no Redis, no cross-process abort, but local aborts still work because the abort route always calls workerAbortControllers.get(runId)?.controller.abort() before delegating to this channel. This module is purely additional cross-replica reach.

Test coverage

Gated on REDIS_URL (see backend/tests/run-abort-pubsub.test.js) — a single-process unit test can't exercise the cross-process semantics; we spin up two real subscriber clients against a real Redis instance and assert (a) both receive the message, (b) the publisher self-suppresses.