fix(core): add stream idle watchdog for silent responses

[Alexxigang]

Summary

• What changed:
  • adds an idle watchdog around streamed next() calls in GeminiChat
  • links the caller abort signal into an internal controller so stalled provider streams can be cancelled safely
  • surfaces silent-stream timeouts as InvalidStreamError('STREAM_IDLE_TIMEOUT') and reuses existing transient retry handling
  • adds regression coverage for timeout, timer reset on progress, and env-based disablement
• Why it changed:
  • some provider SSE streams can go silent without closing, which leaves the CLI hanging indefinitely
• Reviewer focus:
  • timeout / abort lifecycle cleanup
  • retry behavior after STREAM_IDLE_TIMEOUT
  • env gating (QWEN_CODE_STREAM_IDLE_TIMEOUT_MS, QWEN_CODE_DISABLE_STREAM_WATCHDOG)

Validation

• Commands run:

  cd packages/core
  npx vitest run src/core/geminiChat.test.ts -t "stream idle watchdog"
  npm run test -- src/core/geminiChat.test.ts
  npm run lint -- src/core/geminiChat.ts src/core/geminiChat.test.ts
  npm run typecheck
  npm run build

• Prompts / inputs used:
  • mocked silent async generator with no further chunks
  • mocked delayed chunk stream with 30ms gaps under a 50ms timeout
• Expected result:
  • silent streams retry and then fail instead of hanging forever
  • streams that continue making progress within the timeout complete normally
  • the watchdog can be disabled via env for debugging
• Observed result:
  • all focused tests pass, plus full geminiChat.test.ts, lint, typecheck, and build
• Quickest reviewer verification path:
  • set QWEN_CODE_STREAM_IDLE_TIMEOUT_MS=50
  • run the new stream idle watchdog tests in src/core/geminiChat.test.ts
  • inspect makeApiCallAndProcessStream() and processStreamResponse() for cleanup and retry flow
• Evidence (output, logs, screenshots, video, JSON, before/after, etc.):
  • 91 tests passed in src/core/geminiChat.test.ts
  • npm run lint, npm run typecheck, and npm run build all completed successfully

Scope / Risk

• Main risk or tradeoff:
  • very slow but still healthy streams may now timeout if the configured threshold is set too low
• Not covered / not validated:
  • live end-to-end reproduction against a real flaky network/provider stream
• Breaking changes / migration notes:
  • none
  • new optional env vars: QWEN_CODE_STREAM_IDLE_TIMEOUT_MS, QWEN_CODE_DISABLE_STREAM_WATCHDOG

Testing Matrix

	🐗	🐰	🐂
npm run	✅	N/A	✅
npx	✅	N/A	N/A
Docker	N/A	N/A	N/A
Podman	N/A	N/A	N/A
Seatbelt	N/A	N/A	N/A

Testing matrix notes:

• Verified in the local packages/core workspace only.

Linked Issues / Bugs

Fixes #4177

[wenshao]

[Critical] JSDoc @example code fence markers are damaged — double backticks (``ts / ``) instead of triple backticks (```ts / ```). This breaks JSDoc rendering for sendMessageStream.

Suggested change

	* ``ts
	* ```ts
	* const chat = ai.chats.create({model: 'gemini-2.0-flash'});
	* const response = await chat.sendMessageStream({
	* message: 'Why is the sky blue?'
	* });
	* for await (const chunk of response) {
	* console.log(chunk.text);
	* }
	* ```

— DeepSeek/deepseek-v4-pro via Qwen Code /review

[wenshao]

[Suggestion] Each stream chunk in the hot while(true) loop allocates a new Promise.race + 2 setTimeout/clearTimeout pairs + 3 Promise objects via streamWatchdog.next(). For a stream with 20-50 chunks this creates measurable overhead. Consider lifting the timeout timer outside the loop and using timeoutId.refresh() per chunk (Node.js timer refresh API) to eliminate per-chunk timer churn while preserving the idle-detection guarantee.

— DeepSeek/deepseek-v4-pro via Qwen Code /review

[wenshao]

[Suggestion] retryWithBackoff receives only params.config?.abortSignal (the user's signal), not the internal streamAbortController.signal. When the stream idle watchdog fires during a retry delay, retryWithBackoff won't notice the internal abort and will wait the full delay before calling apiCall — which will then immediately fail because streamAbortController.signal is already aborted. Consider passing streamAbortController.signal (or a combined signal) to retryWithBackoff so internal aborts skip unnecessary retry delays.

— DeepSeek/deepseek-v4-pro via Qwen Code /review