[hartmark]

Summary

OpenRouter (and similar OpenAI-compatible aggregators) can send an HTTP 200 SSE stream whose body carries a chat.completion.chunk with empty choices and a top-level error object instead of any delta — e.g. the underlying provider hitting its own capacity limit mid-request. The Responses-API response translator's !chunk.choices?.length branch treated this exactly like a legitimate trailing-usage/no-op chunk, so the stream silently ended with response.completed / error: null / output: [] — a false "successful but empty" response masking a real 502 provider_unavailable failure.

Live repro: a real production request (OpenRouter, nvidia/nemotron-3-ultra-550b-a55b:free) got HTTP 200 with 0 tokens in/out after Nvidia returned "Worker local total request limit reached (33/32)" mid-stream; the client saw an empty completed response with no indication anything failed, which surfaced downstream as a confusing agent-side "couldn't generate a response" failure with zero diagnostic signal.

Mirrors the existing Gemini mid-stream error fix (#4177): sets state.upstreamError from the in-band error chunk so stream.ts's existing upstreamError handling takes over (sendCompleted emits status: "failed" with a real error object instead of a fabricated empty success).

Test plan

• tests/unit/openrouter-midstream-error-chunk.test.ts (new, 2 tests) — TDD: confirmed RED before the fix (chunk silently dropped, state.upstreamError never set), GREEN after. Covers the 502 case and a 429 rate-limit-coded case.
• Full existing translator regression suite (responses-translation-fixes, responses-additional-tools, responses-chat-translation-gaps, responses-handler, responses-usage-trailing-6906, gemini-midstream-error-4177, gemini-midstream-responses, combo-responses-sse-failure-fallback) — all pass, no regressions.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[diegosouzapw]

Thanks, @hartmark! 🙏 Merged — surfaces OpenRouter-style mid-stream aggregator errors (HTTP 200 SSE with empty choices + top-level error) as a real upstream error instead of a false empty-success, so combo fallback kicks in. Rebased onto the current release tip and rebaselined openai-responses.ts for the +26 own-growth. Test 2/2 green.