feat(stovepipe): reconcile dead-lettered build signals and free the slot - #565
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A buildsignal message that dead-letters ends the only poll chain watching a build that is still running, and its request keeps holding one of the queue's in_flight_count slots. With no reconciler on that topic the count stays high for good, so the queue loses a slot per incident until it can no longer admit work. Add the buildsignal DLQ controller, which maps the dead-lettered build back to its request, marks the request failed, and releases the slot, and register it plus its topic in the reference server. Also document in the RFC that the stage's "classifier decides" disposition for Status failures only works if the BuildRunner backend classifies its own transport and HTTP errors. Unclassified, they take the non-retryable default, which is what sends a poll message to the DLQ on the first proxy blip.
Review question on the buildsignal reconciler: failRequest releases the queue slot only for a request in processing, so does it need to widen that? It does not. Processing is the only non-terminal state that can own a slot: process claims the slot and CAS-marks accepted->processing, compensating its own claim when that CAS does not land, and processing exits only to a terminal outcome, which releases the slot itself. Releasing for accepted would decrement for the common request that never claimed one, over-admitting against MaxConcurrent. Say that where failRequest gates on the state, note at the buildsignal call site that a build row implies processing-or-terminal, and pin the intent on the accepted test case, which passes no queue expectations.
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What?
Add buildsignal dlq controller implementation
Why?
A buildsignal message that dead-letters ends the only poll chain watching a build that is still running, and its request keeps holding one of the queue's in_flight_count slots. With no reconciler on that topic the count stays high for good, so the queue loses a slot per incident until it can no longer admit work.
Add the buildsignal DLQ controller, which maps the dead-lettered build back to its request, marks the request failed, and releases the slot, and register it plus its topic in the reference server.
Also document in the RFC that the stage's "classifier decides" disposition for Status failures only works if the BuildRunner backend classifies its own transport and HTTP errors. Unclassified, they take the non-retryable default, which is what sends a poll message to the DLQ on the first proxy blip.
Test Plan