fix(core): preserve thoughtSignature in functionCall parts to fix 400 error

[Tejas-Raj01]

PR Title

fix(core): preserve thoughtSignature in functionCall parts to fix 400 error

---

PR Body

Summary

Fixes a regression introduced in version 0.53.0 that causes a 400 Bad Request error during parallel tool calls. The thoughtSignature was being inadvertently stripped from functionCall parts during history mapping and scrubbing.

Details

• Updated the ToolCallRecord and related interfaces in packages/core/src/scheduler/types.ts and packages/core/src/services/chatRecordingTypes.ts to include the optional thoughtSignature property.
• Modified the mapping logic in packages/core/src/utils/sessionUtils.ts to preserve thoughtSignature when converting tool calls to parts.
• Added a unit test case in packages/core/src/utils/sessionUtils.test.ts to ensure the signature is maintained in the output.

Related Issues

Fixes #28579

How to Validate

1. Run the test suite to ensure the new unit test passes:
   npx vitest run packages/core/src/utils/sessionUtils.test.ts
2. Start the CLI locally:
   npm start
3. Issue a prompt that forces the model to use parallel tool calling (e.g., "Check the weather in New York and London at the same time using your weather tool").
4. Verify that the CLI successfully executes the tools and returns the response without throwing the 400 Bad Request: Function call is missing a thought_signature API error.

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any)
• Validated on required platforms/methods:
  • MacOS
    • npm run
    • npx
    • Docker
    • Podman
    • Seatbelt
  • Windows
    • npm run
    • npx
    • Docker
  • Linux
    • npm run
    • npx
    • Docker

[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 regression where the thoughtSignature was being stripped from function call parts during session history processing. By updating the core data structures and mapping logic, the system now correctly preserves this signature, preventing API errors during parallel tool execution.

Highlights

• Regression Fix: Resolved a 400 Bad Request error occurring during parallel tool calls by ensuring the thoughtSignature property is correctly preserved during history mapping.
• Type Definitions: Updated ToolCallRequestInfo and ToolCallRecord interfaces to include the optional thoughtSignature property.
• Testing: Added a new unit test in sessionUtils.test.ts to verify that thoughtSignature is maintained in the model's output history.

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[github-actions]

📊 PR Size: size/M

• Lines changed: 72
• Additions: +72
• Deletions: -0
• Files changed: 6

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[gemini-code-assist]

Code Review

This pull request introduces support for preserving and propagating thoughtSignature across tool calls, updating relevant interfaces, stream hooks, session utilities, and tests. Feedback suggests ensuring that the optional id property in useGeminiStream.ts falls back to tool.request.callId when undefined, rather than being conditionally omitted, to prevent potential API errors.

[gemini-cli]

Hi there! Thank you for your interest in contributing to Gemini CLI.

To ensure we maintain high code quality and focus on our prioritized roadmap, we only guarantee review and consideration of pull requests for issues that are explicitly labeled as 'help wanted'.

This PR will be closed in 7 days if it remains without that designation. We encourage you to find and contribute to existing 'help wanted' issues in our backlog! Thank you for your understanding.

[Tejas-Raj01]

Hi @scidomino, @galdawave, @DavidAPierce,
I've opened PR #28586 which fixes this P2 regression and includes the necessary unit tests. Could someone please review it and apply the 'help wanted' label to the original issue so the bot doesn't close this PR?

[gemini-cli]

This pull request is being closed as it has been open for 14 days without a 'help wanted' designation. We encourage you to find and contribute to existing 'help wanted' issues in our backlog! Thank you for your understanding.