Fix: Handle truncated write_to_file responses for large files (>7k lines)

[roomote]

Related GitHub Issue

Closes: #6247

Roo Code Task Context (Optional)

Description

This PR fixes a critical issue where the write_to_file tool silently truncates content when writing large files (>7000 lines). The AI assistant would report success despite the file being incomplete due to hitting output token limits (~8000-8192 tokens).

Key implementation details:

• Added detection for files >7000 lines when line_count parameter is missing
• Added validation to compare actual vs predicted line count with 10% tolerance
• Provides clear error messages when truncation is detected, suggesting alternatives like apply_diff or chunking
• Added comprehensive test coverage for large file scenarios

The fix ensures that users are properly notified when file content might be truncated, preventing silent data loss.

Test Procedure

How I tested:

1. Added unit tests in src/core/tools/__tests__/writeToFileTool.spec.ts covering:
   • Detection of large files (>7000 lines) without line_count
   • Line count mismatch detection with 10% tolerance
   • Proper error messages and suggestions
2. Ran all existing tests to ensure no regression: cd src && npx vitest run
3. All tests pass successfully

How reviewers can verify:

1. Run the test suite: cd src && npx vitest run core/tools/__tests__/writeToFileTool.spec.ts
2. Review the new test cases that simulate large file scenarios
3. Check the error handling logic in writeToFileTool.ts

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: New and/or updated tests have been added to cover my changes (if applicable).
• Documentation Impact: I have considered if my changes require documentation updates (see "Documentation Updates" section below).
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Screenshots / Videos

Not applicable - this is a backend fix for tool behavior.

Documentation Updates

• No documentation updates are required.

The error messages themselves provide clear guidance to users when truncation is detected.

Additional Notes

This fix addresses a critical data loss issue that affects users working with large files. The 7000-line threshold was chosen based on typical token limits and file size patterns observed in the issue report.

Get in Touch

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Important

Fixes truncation issue in write_to_file tool for large files by adding detection and validation mechanisms.

• Behavior:
  • Detects files >7000 lines in writeToFileTool.ts and checks for truncation if line_count is missing.
  • Validates line count with 10% tolerance and provides error messages for mismatches.
  • Suggests alternatives like apply_diff or chunking when truncation is detected.
• Tests:
  • Added tests in writeToFileTool.spec.ts for large file detection, line count mismatch, and error messaging.
  • Tests cover scenarios with exact line count matches and small differences within tolerance.
• Misc:
  • No changes to existing functionality outside of truncation handling.

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[daniel-lxs]

Closing as the issue is not properly scoped