fix(editor): make tab close best-effort in DiffViewProvider.open

[0xMink]

Closes #11362

Summary

• DiffViewProvider.open() closes existing editor tabs for the file being edited before opening the diff view. The tabGroups.close(tab) call is unguarded — if the tab reference becomes invalid between lookup and close, it throws "Tab close: Invalid tab not found!" and aborts the entire edit operation.
• This is best-effort cleanup; failure should not block the edit flow.
• Wraps the tabGroups.close(tab) call in a try-catch, matching the existing defensive pattern in closeAllDiffViews() in the same file.
• The documentWasOpen flag assignment remains unconditional and outside the close success path (it tracks whether the file had an open tab, not whether the close succeeded).
• VS Code has an upstream regression producing the same error string (Tab list gets corrupted when a new webview is opened (extension API) microsoft/vscode#228270); this change treats close failures defensively regardless of trigger.

Test plan

• Existing: 15/15 DiffViewProvider tests passing
• Manual: open a file in the editor, trigger a Roo edit on that file, verify the diff view opens and editing proceeds normally
• Manual (WSL/remote): same flow in a remote environment where the race window is wider

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Important

Wrap tabGroups.close(tab) in DiffViewProvider.open() with try-catch to prevent aborting edit operation on tab close failure.

• Behavior:
  • Wraps tabGroups.close(tab) in DiffViewProvider.open() with try-catch to prevent aborting edit operation on tab close failure.
  • documentWasOpen flag remains outside try-catch to track if file had an open tab.
• Context:
  • Matches defensive pattern in closeAllDiffViews().
  • Addresses similar error in VS Code (Tab list gets corrupted when a new webview is opened (extension API) microsoft/vscode#228270).
• Testing:
  • 15/15 existing tests passing.
  • Manual tests for local and remote environments confirm normal operation.

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[roomote]

Rooviewer   See task

Reviewed the change. No issues found -- this is a clean, minimal defensive fix. The try-catch around tabGroups.close(tab) in open() correctly matches the existing pattern in closeAllDiffViews(), and the documentWasOpen flag stays outside the error-handling block as intended. All 15 existing tests pass.

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[0xMink]

Related work

Note for reviewers: PR #11327 (preserve pinned tab state) modifies the same for (const tab of tabs) loop in DiffViewProvider.open(). If both PRs merge, they should be reconciled — the try-catch from this PR should wrap the tabGroups.close() call, while the pin-state capture from #11327 should happen before it.

Precedent: the defensive close pattern used here matches the existing posture in closeAllDiffViews(), introduced in PR #4578.