Best possible solution:

Land the Google-owned transport fix once required CI is green, keeping the activity signal within the existing AssistantMessageEvent protocol.

Do we have a high-confidence way to reproduce the issue?

Yes for the transport liveness gap: current main parses signature-only Google SSE parts without yielding an event, while the idle watchdog only resets after yielded events. The full production hang still depends on live Gemini behavior, which was not rerun in this read-only review.

Is this the best way to solve the issue?

Yes. Handling signature-only chunks in the Google transport with an empty thinking_delta is narrower than changing the core idle-timeout wrapper and stays within the pinned stream event contract.

What I checked:

• Current main skips signature-only Google parts: The current Google SSE loop only enters the content-block path when part.text is a string, so a part with only thoughtSignature is parsed without yielding a stream event. (extensions/google/transport-stream.ts:800, 473fc0aad84a)
• Idle watchdog depends on yielded events: streamWithIdleTimeout races each streamIterator.next() against the timer and clears it only after next() resolves, so parsed provider activity that does not yield cannot refresh liveness. (src/agents/pi-embedded-runner/run/llm-idle-timeout.ts:127, 473fc0aad84a)
• PR uses existing event protocol: The latest PR diff converts signature-only parts into thinking blocks and emits an empty thinking_delta, replacing the earlier out-of-contract custom event approach. (extensions/google/transport-stream.ts:797, 534445c29841)
• Pinned dependency contract checked: @mariozechner/[email protected] defines thinking_start, thinking_delta, and thinking_end in AssistantMessageEvent; it does not define thinking_signature. (package.json:1659, 473fc0aad84a)
• Regression coverage added: The PR adds two Google transport fixtures covering a signature-only part during an existing thinking block and one arriving before any text. (extensions/google/transport-stream.test.ts:767, 534445c29841)
• Changelog coverage added: The PR adds an active CHANGELOG.md fix entry for the Google/Gemini idle-timeout behavior and credits the reporter and contributor. (CHANGELOG.md:33, 534445c29841)

Likely related people:

• steipete: Recent path history shows Google transport extraction, Google thinking behavior, Vertex auth, and idle-timeout policy work, and current-main blame covers the Google stream loop in this shallow checkout. (role: recent maintainer / adjacent owner; confidence: high; commits: 85826c83e4a1, cc0f3067a003, 0b59964ec945; files: extensions/google/transport-stream.ts, extensions/google/transport-stream.test.ts, src/agents/pi-embedded-runner/run/llm-idle-timeout.ts)
• liuy: GitHub path history attributes the original LLM idle-timeout streaming watchdog to this contributor, which is the core liveness behavior exposed by the Google transport gap. (role: introduced behavior; confidence: medium; commits: 84b72e66b918; files: src/agents/pi-embedded-runner/run/llm-idle-timeout.ts)
• ericberic: Recent Google transport and test history includes Gemini thinking-budget fixes in the same provider test surface touched by this PR. (role: recent Google transport contributor; confidence: medium; commits: edca8c721a69; files: extensions/google/transport-stream.ts, extensions/google/transport-stream.test.ts)
• obviyus: Current history shows adjacent work unifying idle timeout with the runner abort path, which is relevant to the liveness boundary this PR exercises. (role: adjacent idle-timeout maintainer; confidence: medium; commits: 179f713c88c6; files: src/agents/pi-embedded-runner/run/llm-idle-timeout.ts)

Remaining risk / open question:

• Two GitHub check-runs were still in progress in the reviewed snapshot; merge should wait for required CI to finish.
• This read-only review did not perform a live Gemini 3.1 end-to-end run; confidence comes from the deterministic transport fixture and the linked issue's provider evidence.

Codex review notes: model gpt-5.5, reasoning high; reviewed against 473fc0aad84a.