[Zartharas]

Summary

• Apply requestQueue.maxWaitMs only while a request waits for limiter admission, not while an admitted upstream request is executing.
• Prevent timed-out queued placeholders from starting upstream work later.
• Classify local queue timeout, full, and wedge conditions as local capacity errors rather than provider failures.
• Prevent local limiter errors from poisoning connection health or cascading through combo retries and fallback targets.

Problem

The rate limiter passed requestQueue.maxWaitMs to Bottleneck as job expiration. Bottleneck applied that deadline to the complete scheduled job, including an already-running upstream request.

A slow but valid request could therefore be rejected locally even though the provider had not failed. The resulting local error was surfaced as a provider-style 503, which could mark accounts or models unavailable, rotate through other connections, and amplify one timeout into repeated fallback calls.

The underlying upstream request could also remain active after the wrapper timed out and continue consuming local concurrency.

Fix

• Add queue-wait-only scheduling through scheduleWithQueueWaitBudget.
• Once admitted, let existing upstream timeout and cancellation controls govern execution.
• Ensure timed-out or aborted queued placeholders cannot invoke upstream work later.
• Map RATE_LIMIT_QUEUE_TIMEOUT, RATE_LIMIT_QUEUE_FULL, and RATE_LIMIT_QUEUE_WEDGED to HTTP 429 with type local_queue_capacity.
• Treat these errors as request-scoped and skip connection disablement.
• Return local queue-capacity responses from priority and round-robin combos without retrying or rotating targets.

Validation

Focused regression tests passed for:

• queue timeout before admission
• prevention of delayed upstream execution
• long-running admitted requests exceeding maxWaitMs
• queued-request cancellation
• local capacity classification
• prevention of combo retry/fallback amplification
• limiter wedge recovery
• queue-depth admission control
• existing connection-disable guards

Focused ESLint validation passed for all modified source and test files.

Files Changed

• open-sse/services/rateLimitManager.ts
• open-sse/services/rateLimitManager/admission.ts
• open-sse/handlers/chatCore.ts
• open-sse/services/combo/comboPredicates.ts
• open-sse/services/combo.ts
• tests/unit/rate-limit-queue-timeout-message-4165.test.ts
• tests/unit/rate-limit-local-capacity-classification.test.ts