fix(vscode-ide-companion): preserve terminal focus when closing diff tabs

[gaurav0107]

Summary

When using the VS Code companion extension, approving a file edit in the
Gemini CLI closes the background diff preview and steals keyboard focus from
the integrated terminal. The user then has to click back into the terminal
before every subsequent edit. This change keeps focus in the terminal by
passing VS Code's preserveFocus flag when the diff tab is closed.

Details

The companion opens the diff preview as a background tab (vscode.diff with
preserveFocus: true) while the user works in the terminal where the Gemini
CLI runs. On closeDiff, DiffManager.closeDiffEditor in
packages/vscode-ide-companion/src/diff-manager.ts closes that tab with
vscode.window.tabGroups.close(tab). VS Code's default behavior when a tab is
closed is to move focus into the editor area. Passing the second positional
argument to TabGroups.close(tabs, preserveFocus?) as true keeps focus in
its current position (the terminal):

await vscode.window.tabGroups.close(tab, true);

This is a one-line behavioral fix plus a focused regression test.

It resurrects the one-line fix that was reviewed and approved by @kschaab
in #23215, which was auto-closed by the 30-day inactivity bot rather than on
merits (the alternative #22331 is closed). #23215 shipped without a test; this
PR adds the missing regression coverage in src/diff-manager.test.ts,
asserting tabGroups.close is invoked with preserveFocus = true when a diff
tab is closed (the test fails on the old close(tab) call and passes with the
fix).

Related Issues

Fixes #22193

How to Validate

Automated:

• npm test -w packages/vscode-ide-companion — the new src/diff-manager.test.ts
  passes and the full package suite is green (41 passed, 1 skipped).
• npm run lint -w packages/vscode-ide-companion and tsc --noEmit pass.

Manual (validation steps from #23215):

1. Build the companion extension: npm run build -w packages/vscode-ide-companion
2. Start the Gemini CLI in VS Code's integrated terminal.
3. Prompt Gemini to make a code edit that requires user approval.
4. When prompted with [Proceed] in the terminal, press Enter.
5. Focus should remain in the terminal, and the next Enter keypress should act
   on the CLI instead of inserting a newline in an editor tab.

Pre-Merge Checklist

• Updated relevant documentation and README (none required for this fix)
• Added/updated tests (regression test for Gemini CLI doesn't maintain keyboard focus when VS Code extension closes a diff #22193)
• Noted breaking changes (none)
• Validated on required platforms/methods:
  • macOS
    • npm run (manual GUI validation pending)

Note: I am a first-time contributor to this organization and still need to
sign the Google CLA at https://cla.developers.google.com/ when googlebot
comments. The automated checks above pass; manual GUI focus validation is
pending a local VS Code session.

[github-actions]

📊 PR Size: size/M

• Lines changed: 116
• Additions: +115
• Deletions: -1
• Files changed: 2

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! 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 addresses a usability issue where closing a diff preview tab in the VS Code companion extension causes the editor to steal keyboard focus from the integrated terminal. By ensuring the preserveFocus flag is passed during tab closure, the extension now maintains the user's focus in the terminal, improving the workflow for Gemini CLI interactions.

Highlights

• Preserve Terminal Focus: Updated the diff tab closure logic to pass the preserveFocus: true flag, preventing the editor from stealing focus from the integrated terminal when a diff is closed.
• Regression Testing: Added a new test suite in diff-manager.test.ts to verify that vscode.window.tabGroups.close is correctly invoked with the preserveFocus parameter.

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[gemini-code-assist]

Code Review

This pull request updates the DiffManager to pass preserveFocus=true when closing background diff tabs, ensuring that keyboard focus remains in the integrated terminal. A new test suite is added to verify this behavior. The review feedback correctly points out that vscode.window.tabGroups.all should be reset in beforeEach to prevent test pollution and ensure proper test isolation.