fix(core): handle AbortError thrown during processTurn

[MumuTW]

Summary

• catch AbortError in GeminiClient.sendMessageStream() when thrown from async work inside processTurn
• map that path to a graceful UserCancelled event instead of allowing the stream generator to throw
• add a regression test that forces processTurn setup (loopDetector.turnStarted) to reject with AbortError

Why

Issue #21122 reports unhandled AbortError crashes during stream generation. Some aborts can surface from processTurn internals before Turn.run() has a chance to convert them into stream events. This patch handles that boundary safely.

Testing

• pnpm -C packages/core test -- src/core/client.test.ts (failed in this environment because vitest is not installed in local workspace path)
• pre-commit checks ran successfully during commit (prettier + eslint on changed files)

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an issue where unhandled AbortError exceptions could cause crashes during stream generation. It introduces robust error handling within the processTurn method to catch these errors and convert them into a UserCancelled event, preventing application instability and providing a more predictable termination for aborted operations.

Highlights

• Error Handling: Implemented a catch block within processTurn to gracefully handle AbortError exceptions that may arise from asynchronous operations.
• Event Mapping: Mapped caught AbortError instances to a GeminiEventType.UserCancelled event, ensuring a consistent and expected stream termination.
• Regression Testing: Added a new regression test case to validate that processTurn correctly yields a UserCancelled event when an AbortError is thrown.

Changelog

• packages/core/src/core/client.test.ts
  • Added a new test case to verify that sendMessageStream yields UserCancelled when processTurn throws an AbortError.
• packages/core/src/core/client.ts
  • Imported isAbortError from ../utils/errors.js.
  • Wrapped the processTurn logic in a try-catch block to intercept AbortError and signal.aborted conditions.
  • Yielded GeminiEventType.UserCancelled and returned early if an AbortError is caught or the signal is aborted.

Activity

• The author reported that local tests failed due to a missing dependency (vitest not installed in the local workspace path).
• Pre-commit checks (prettier + eslint) ran successfully on changed files.

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[gemini-code-assist]

Code Review

This pull request introduces error handling for AbortError within the sendMessageStream method, wrapping the processTurn generator in a try...catch block to map AbortError to a UserCancelled event and prevent unhandled exceptions. A security audit confirmed that these changes are security-neutral and improve robustness by gracefully handling cancellations, with no high or critical security vulnerabilities identified. A new regression test has also been included to verify this behavior.

[gsquared94]

I think this fix complements #21123