## Summary
`batchTriggerAndWait()` could leave a parent run waiting forever. The
2-phase batch API blocks the parent on the batch's waitpoint as soon as
the batch is created, but the batch is only sealed at the end of item
streaming. If streaming never completed, nothing sealed the batch,
nothing completed the waitpoint, and the parent stayed suspended with no
timeout and no way to recover.
Supersedes #4016, which added the reaper alone.
## Fix
Admission for item streaming was being decided twice. Batch creation
passes its own rate limiter, which fixes `expectedCount` and blocks the
parent, and then the item stream had to pass the general API limiter as
well, competing with unrelated traffic. A second limiter could therefore
veto work the first had already committed the parent to. Creation now
mints a bounded grant that the item stream spends, so an admitted batch
can finish streaming. The grant is capped per batch rather than
exempting the path, and every failure mode (no grant, spent grant,
unreachable store) falls back to the normal limiter.
That makes stranding much rarer but not impossible, since a request
timeout or a crash can still end streaming for good. So a seal-timeout
reaper aborts any batch still unsealed after `BATCH_SEAL_TIMEOUT_MS` and
completes the parent's waitpoint with an error, letting
`batchTriggerAndWait()` reject instead of hang. It is race-safe against
a late seal, and it is only scheduled for batches that actually block a
parent, so fire-and-forget batches cost nothing.
Finally, the batches page used to report "Batch completion checked." for
these batches while doing nothing, because the completion path returns
early on an unsealed batch. It now says the batch cannot be resumed.
Rate limiting is no longer the reason a batch strands, so the reaper's
default stays at 30 minutes, comfortably above the SDK's worst-case
stream-retry budget.
## Verification
Unit and container tests cover the grant cap, the bypass ordering (it
runs after the authorization check, so it can never skip
authentication), and the reaper's abort, seal race, idempotency, and
no-waitpoint cases.
Also verified end-to-end against a running stack. With the general limit
exhausted, batch creation and other API calls returned 429 while a
granted batch still streamed and sealed; an ungranted batch id was rate
limited rather than bypassed; and the grant cut off exactly at its
configured attempt count. Reproducing the stranded state on a real
parent run, the batch was aborted at the timeout, the waitpoint
completed with an error, and the parent resumed and finished instead of
hanging. A parentless batch left unsealed was untouched well past the
reaper window.
## Verified against deployed runs
The reaper was proven end to end with a real deployed run (locally-run
supervisor, containerised
run) and a real network fault, rather than a simulated one: toxiproxy
severs the phase 2 item
stream mid-flight so every SDK stream retry genuinely fails, while phase
1 still succeeds. Only
the batch calls traverse the fault, so control-plane traffic is
untouched.
The reproduction is the shape that actually strands a parent: the task
catches the
`BatchTriggerError` the SDK throws and carries on, so the phase 1 block
outlives the thrown error
and the parent hangs at its next suspension point.
With the reaper disabled, the parent sat in `EXECUTING_WITH_WAITPOINTS`
for over 24 minutes holding
two blockers, and stayed stuck across a full infrastructure restart:
```
type | status | has_timeout
BATCH | PENDING | f <- orphan, completedAfter NULL
DATETIME | COMPLETED | t <- the wait already elapsed
```
With the reaper enabled the same task under the same fault completed in
about 75 seconds with zero
blockers left, the batch `ABORTED`, and its waitpoint completed carrying
the error.
Two conditions are required to observe this at all, which is worth
knowing for any future test:
the run must be deployed rather than `trigger dev` (dev runs execute in
process and finish while
still holding blocker rows), and the wait after the caught error must
exceed the checkpoint
threshold, or it is served in process and never suspends.
### Why completing the batch waitpoint is sufficient
`batchTriggerAndWait` runs create, then stream, then wait. A phase 2
failure throws before the wait
is ever reached, and the reaper only fires on an unsealed batch, so the
parent is never suspended
awaiting the batch when it runs. The parent therefore does not need a
synthetic result, only to stop
being blocked. Note this reasoning depends on that ordering: if the wait
were ever reached with an
unsealed batch, completing the batch waitpoint alone would not settle
the caller.
## Follow-ups
- Batches stranded before this ships still need a one-off recovery; the
reaper only schedules at creation time.
- That same property leaves a gap if the process dies between creating
the batch and scheduling the job. A periodic sweep would close it, but
wants a supporting index.
- When a partially streamed batch aborts, children already enqueued keep
running while the parent fails. Left as-is deliberately, since
cancelling triggered work is a bigger semantic call.
Eric Allam
c72ebf9084