Pacing queue overload surfaces as 502 upstream_error instead of retryable 429 on fetchResponse and rebuildAndRefetch paths #1790

Client or integration

Direct HTTP/API client

Area

Proxy and routing

Summary

waitForProviderRequestSlot throws RequestPacingQueueOverloadError when a provider's request-pacing queue is full. The runTurn path in src/server/responses/core.ts (around line 3247) translates that error into a retryable 429 rate_limit_error event, but the generic transport catches around the initial fetchResponse dispatch (around lines 3451-3480) and rebuildAndRefetch (around lines 3544-3565) convert every error into 502 upstream_error. Under pacing-queue pressure, requests dispatched through those paths receive a 502 instead of the retryable-429 contract used elsewhere for the same condition.

Additionally, noteAttemptSend runs before waitForProviderRequestSlot admits the request on the fetchResponse branch (around line 3457), so overload-rejected requests still inflate the attempt send count.

Reproduction

Found by code review while working on #1743; not yet reproduced at runtime. Code-path walkthrough against dev @ 4b950101a1116d8bac4e479cb2dceca3bb80370e:

1. Configure a provider with request pacing where the queue capacity is small relative to the burst.
2. Send a burst of /v1/responses requests routed through a provider adapter that uses fetchResponse, or trigger the rebuild/refetch retry path.
3. When the pacing queue is full, waitForProviderRequestSlot throws RequestPacingQueueOverloadError (src/server/responses/core.ts:3451 or :3545).
4. The surrounding catch converts it to 502 upstream_error (lines ~3473-3480 / ~3560-3565) instead of the retryable 429 shape the runTurn path produces at ~3247.

Expected: the same retryable-429 mapping as the runTurn path, with noteAttemptSend moved after successful pacing admission so rejected requests do not count as sends.

Version

dev @ 4b950101a1116d8bac4e479cb2dceca3bb80370e (pre-existing path; unchanged by #1743)

Operating system

Linux (Debian 13); the code path is platform-independent

Provider and model

Any forward-auth Responses provider with request pacing configured

Logs or error output

No response

Screenshots and supporting files

No response

Redacted configuration

No response

Checks

• I searched existing issues and documentation.
• I removed secrets, tokens, account details, request credentials, and personal data.