fix: restart resumes the process loop and the pulse emitter

[jbiskur]

Problem

restart() calls stop(true), which clears running, empties the buffer and stops the pulse emitter. The fetch loop revives itself from restartTo:

this.running = true
return this.loop()

But the process loop is a while (this.running) loop and only start() called startProcessLoop(). A pump restarted while it was delivering keeps pulling events and never delivers or checkpoints again — and stops pulsing, so it looks dead to the control plane while its host still reports healthy.

This is the defect written up on 2026-04-14 in Usable fragment 28875215-003d-4770-9d44-8e3488d25246.

Production impact

It stalled two data-pathways pathways for 26 days (2026-08-02 → 2026-08-28):

Pathway	Tenant	Effect
417b8dd9-b6a3-4ce9-b254-6ea12ca97d57	memory-mesh	26-day backlog, drained in 2.4 h at 98% DB CPU
5a32bd1c-9d0c-4aef-a813-4fee60280f8e	flowcore-saas	nothing delivered, assignment reported active

A scoped replay asked for one flow type; the consumer restarted every source, and every restarted pump went quiet.

Change

• ensureProcessLoop() starts the delivery loop whenever the pump is running with a processor and no loop is live. The fetch loop calls it once per iteration, so a loop that exits for any reason comes back within one iteration.
• processLoopRunning guards against a second loop when the existing one is only parked in reserve() — two loops would race over the same buffer.
• A loop that exits while the pump is already running again (the restart landed mid-batch) restarts itself.
• The restart path calls pulseEmitter.start() again. It is already idempotent.

Tests

Three new cases in data-pump-restart.test.ts, all of which fail on the previous behaviour:

1. delivery continues after a restart() issued from inside the handler
2. no second process loop when one is only parked (an event is delivered once, not twice)
3. the pulse emitter is started again

Suite: 57 pass / 0 fail. tsc --noEmit and prettier --check clean.

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