fix: support object-type arguments in tool call parsing

[silencezhoudev]

Description

In certain cases, the toolCall.function.arguments returned by the LLM or intermediate processing layer can be an object rather than a JSON string, which may result in filepath being empty or incorrectly parsed when handling the create_new_file tool call.

This PR adds proper validation and normalization for filepath to ensure file creation works reliably across platforms (including macOS and Windows).

Fixes #9045
Fixes #8764

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Checklist

• I've read the contributing guide
• The relevant docs, if any, have been updated or created
• The relevant tests, if any, have been updated or created

Screen recording or screenshot

N/A (logic fix in agent tool layer)

Tests

• Reproduced the issue on macOS (file creation failed due to empty or invalid filepath)
• Patched the VSCode extension production bundle (out/extension.js) locally to validate the fix in a real plugin environment
• Verified that new files are created correctly after applying filepath validation and path normalization
• Issue is also consistent with the original Windows report in Code writing to file failed #9045

I have read the CLA Document and I hereby sign the CLA

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Summary by cubic

Support object-type tool call arguments to prevent parameter loss and ensure create_new_file gets a valid filepath. Fixes #9045 across macOS and Windows.

• Bug Fixes
  • If toolCall.function.arguments is a non-empty plain object, return it; otherwise parse the JSON string.

^{Written for commit 82f6f69. Summary will update on new commits.}

[github-actions]

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[cubic-dev-ai]

No issues found across 1 file

[RomneyDa]

Makes args parsing a bit more robust 👍