fix(functiontool): recover from panics in user functions

[unbiasedcodex]

Summary

• Add panic recovery to functionTool.Run() to prevent agent crashes when user-provided functions panic
• Panics are converted to errors with descriptive messages including the tool name
• Add test case to verify panic recovery behavior

Resolves the TODO at tool/functiontool/function.go:135:

// TODO: Handle panic -> convert to error.

Test plan

- Added TestFunctionTool_PanicRecovery unit test
- Test creates a function that intentionally panics and verifies:
  - Error is returned (not nil)
  - Result is nil
  - Error message contains "panic in tool" and the tool name
- Ran locally: go test ./tool/functiontool/... -run TestFunctionTool_PanicRecovery -v → PASS

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[gemini-code-assist[bot]]

Summary of Changes

Hello @unbiasedcodex, I'm Gemini Code Assist[^1]! 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 introduces robust error handling to the functionTool component by implementing a panic recovery mechanism. This change prevents agent crashes when user-defined functions unexpectedly panic, instead converting these panics into structured errors. This significantly improves the stability and resilience of the system when interacting with external or potentially unstable user code.

Highlights

• Panic Recovery: Implemented a defer and recover mechanism within the functionTool.Run() method to catch panics that may occur in user-provided functions.
• Error Conversion: Panics caught by the recovery mechanism are now converted into error types, including a descriptive message that specifies "panic in tool" and the name of the tool that panicked.
• Test Coverage: A new unit test, TestFunctionTool_PanicRecovery, has been added to thoroughly verify that the panic recovery mechanism functions as expected, ensuring errors are returned and results are nil upon a panic.

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