fix(run-engine): stop requeued runs with a lapsed ttl being orphaned in the queue (#4669)

## Summary

A run triggered with a `ttl` could get permanently stuck showing as
queued. If the run started executing and was then requeued after a
failure (a stalled heartbeat, a worker dying mid-run) once its TTL had
already elapsed, the next dequeue pass silently dropped it from every
queue structure. The run stayed QUEUED in the database forever, and
nothing (dequeue, the TTL consumer, queue repair) could ever see it
again.

## Root cause

Enqueue registers a TTL entry for the TTL consumer, and the first
dequeue removes it ("the run is executing, not expired"). A nack rewrote
the message preserving the original `ttlExpiresAt` without
re-registering that entry. The next dequeue pass then took the
expired-TTL branch: remove the run from the queue sorted sets and leave
the message for the TTL consumer to finalize. But the consumer's entry
was gone, so nothing ever finalized the run.

The fix has two halves:

- `nackMessage` drops `ttlExpiresAt` from the rewritten message. TTL
only applies to runs that have never been dequeued (the same contract as
`includeTtl` on re-enqueues), so a requeued run stays dequeuable and is
never expired by its original deadline.
- The dequeue expired-TTL branches now (re-)register the TTL entry
instead of assuming it exists, so any message still carrying a lapsed
`ttlExpiresAt` with no TTL entry (including ones written before this
fix) finalizes as EXPIRED instead of orphaning.

## Verification

New engine test suite `ttlNackRequeue.test.ts` (testcontainers, real
Redis and Postgres). All four tests fail before the fix and pass after:

- a heartbeat-stalled EXECUTING run with a lapsed TTL is requeued and
dequeued again instead of orphaned (the full production failure chain)
- requeue-after-failure strips `ttlExpiresAt` so later dequeues do not
treat the run as expired
- a lapsed-TTL message whose TTL entry is missing is re-registered by
dequeue and finalized as EXPIRED, for both plain and concurrency-key
queues

Also ran the existing ttl, heartbeats, dequeuing and attemptFailures
engine suites plus the full run-queue suite (149 tests) against the
change.

Author: matt-aitken

.server-changes/ttl-runs-no-longer-stuck-after-requeue.md

@@ -0,0 +1,6 @@
+---
+area: webapp
+type: fix
+---
+
+Runs triggered with a `ttl` could get permanently stuck in the queued state if they started executing and were then requeued after a failure (for example a worker dying mid-run) once the TTL had already elapsed. Requeued runs now dequeue normally: a run's TTL only applies while it is waiting to start for the first time.