fix: resolve diff editor issues with markdown preview associations (#4946)

[daniel-lxs]

Description

Fixes #2360

This PR resolves an issue where file editing tools (apply_diff, write_to_file, search_and_replace) fail for files that have custom editor associations configured in VS Code, particularly markdown files with preview mode associations.

Root Cause

When VS Code has workbench.editorAssociations configured to open certain file types (like "*.md": "vscode.markdown.preview.editor"), the vscode.diff command opens the file in preview mode instead of as an editable text document. This causes:

1. "Illegal value for lineNumber" errors when trying to edit
2. Diff views that can't be properly detected and closed

Solution

Implemented a simple and reliable approach:

1. Pre-open files as text documents: Before executing the diff command, always call vscode.window.showTextDocument() with preview: false to ensure the file opens in text editing mode
2. Enhanced diff view detection: Updated closeAllDiffViews() to identify diff tabs both by URI scheme and by label pattern ("↔ Roo's Changes")

This PR doesn't affect the normal behavior of editing files at all. Files were being opened when edited, but this happened after the edit itself. Now it happens before the edit. Ultimately, the result is exactly the same.

Changes Made

• src/integrations/editor/DiffViewProvider.ts:

  • Modified openDiffEditor() to pre-open files as text documents before executing diff command
  • Enhanced closeAllDiffViews() to detect diff views by label pattern as fallback
  • Added comprehensive comments explaining the fix

• src/integrations/editor/__tests__/DiffViewProvider.spec.ts:

  • Updated mocks to include all required VSCode APIs
  • Added tests verifying the pre-opening behavior
  • Added tests for enhanced diff view closing logic
  • All existing tests continue to pass

Testing

• All existing tests pass
• Added new tests for pre-opening behavior
• Added tests for enhanced diff view detection
• Manual testing with markdown files and preview associations
• Verified no performance regression

Verification of Acceptance Criteria

• File editing tools work correctly with markdown files that have preview associations
• Diff views are properly opened and closed
• No "Illegal value for lineNumber" errors
• Solution works for all file types, not just markdown
• Backward compatibility maintained

Impact

• Positive: Fixes a blocking issue for users with custom editor associations
• Performance: Minimal impact - adds one additional showTextDocument call per diff operation
• Compatibility: Fully backward compatible, no breaking changes
• Scope: Affects only the diff editor functionality

Screenshots/Demo

Before: File editing tools would fail with "Illegal value for lineNumber" errors for markdown files with preview associations.

After: File editing tools work seamlessly regardless of editor associations.

Checklist

• Code follows project style guidelines
• Self-review completed
• Comments added for complex logic
• All tests pass
• No breaking changes
• Issue requirements fully addressed

---

Important

Fixes diff editor issues in VS Code by pre-opening files as text documents and enhancing diff view detection.

• Behavior:
  • Fixes issue with vscode.diff command opening files in preview mode due to workbench.editorAssociations.
  • Pre-opens files as text documents using vscode.window.showTextDocument() with preview: false.
  • Enhances closeAllDiffViews() in DiffViewProvider.ts to detect diff views by URI scheme and label pattern.
• Testing:
  • Updates DiffViewProvider.spec.ts to mock necessary VSCode APIs.
  • Adds tests for pre-opening behavior and enhanced diff view detection.
  • Verifies no performance regression and maintains backward compatibility.

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[mrubens]

Looks good other than the comment about using a constant for Original ↔ Roo's Changes and looking for that