fix(core): guard message inspectors against empty parts arrays

[AriaZhao-coder]

Summary

isFunctionCall() and isFunctionResponse() in packages/core/src/utils/messageInspectors.ts returned true for messages with an empty parts array, because [].every(...) is vacuously true in JavaScript.

As a result:

• any role: "model" message with parts: [] was misclassified as a function call, and
• any role: "user" message with parts: [] was misclassified as a function response.

These helpers are consumed by the routing, loop-detection, and chat subsystems, so the false positives can propagate incorrect behavior across the agent.

Fix

Add a parts.length > 0 guard to both functions so empty-parts messages are correctly treated as neither a function call nor a function response.

content.role === 'user' &&
!!content.parts &&
content.parts.length > 0 &&            // added
content.parts.every((part) => !!part.functionResponse)

Tests

The file previously had no test coverage. Added messageInspectors.test.ts with 12 tests covering both functions: valid calls/responses, wrong role, non-matching parts, mixed parts, undefined parts, and the empty-array regression case.

Verified locally (Node 20):

• vitest run — new tests pass (12/12); affected callers (routing strategies, loop detection, nextSpeaker) still pass (131/131)
• prettier --check, eslint --max-warnings 0, tsc --noEmit — all clean

Fixes #23195
Fixes #22912

[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 a logic error in the message inspection utilities where empty parts arrays were causing false positives for function call and response classification. By enforcing a non-empty parts array requirement, the fix ensures more accurate message handling across the agent's subsystems.

Highlights

• Bug Fix: Added a length check to ensure messages with empty parts arrays are not incorrectly identified as function calls or responses.
• Test Coverage: Introduced comprehensive unit tests in a new test file to validate function inspector logic and prevent future regressions.

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[github-actions]

📊 PR Size: size/M

• Lines changed: 113
• Additions: +113
• Deletions: -0
• Files changed: 2

[gemini-code-assist]

Code Review

This pull request updates the isFunctionResponse and isFunctionCall utility functions in packages/core/src/utils/messageInspectors.ts to ensure they return false when the parts array is empty. Additionally, a new test file packages/core/src/utils/messageInspectors.test.ts has been added to thoroughly test these utilities. There are no review comments, and I have no feedback to provide.