[BUG] Inconsistent preserveFocus on diff-open calls causes IME composition loss (VS Code extension)

Start with the three vscode.diff call sites described in extension.js, especially site 3 where the options omit preserveFocus. Compare it with sites 1 and 2, then add the suggested regression test or lint coverage so all diff invocations preserve focus. Done means the affected call consistently passes preserveFocus: true and the relevant check passes.

[BUG] Inconsistent preserveFocus on diff-open calls causes IME composition loss (VS Code extension)

Summary

When Claude Code opens a file-edit diff, it always opens a new editor tab (preview:false, hardcoded, no user setting — same underlying behavior as #42288/#52832/#43619). This report focuses on a more severe side effect: on at least one code path, the diff is opened without preserveFocus: true, which steals editor focus away from the chat input. If the user is mid-composition in an IME (Japanese/Chinese/Korean/Vietnamese input), the forced focus change fires compositionend prematurely, committing the unconverted candidate text and silently corrupting/losing what the user was typing.

Evidence (from extension.js, v2.1.211)

Three call sites invoke vscode.diff with distinct option objects:

I = { preview: false, preserveFocus: true }   // site 1
b = { preview: false, preserveFocus: true }   // site 2
v = { preview: false }                        // site 3 - preserveFocus NOT set (defaults to false)

Site 3 is the outlier and the likely source of focus theft.

Steps to reproduce

1. Set OS/input method to Japanese (or any IME-based language) and open the Claude Code chat panel in VS Code.
2. Start typing a message with kanji conversion in progress (composition not yet confirmed).
3. While still mid-composition, trigger a file edit from Claude (or have an in-flight edit complete) that opens a new diff tab via the "site 3" path.
4. Observe: the in-progress IME candidate is committed/lost as unconverted text, and the diff tab now has focus instead of the chat input.

Expected behavior

All diff-opening code paths should consistently pass preserveFocus: true (matching sites 1 and 2), so opening a diff never steals focus from wherever the user is actively typing.

Suggested fix

Add preserveFocus: true to the options object at site 3, and add a regression test / lint rule ensuring all vscode.diff invocations in this extension share the same focus-handling options.

Related (broader "opens in new tab" complaints, not IME-specific)

• #42288, #52832, #43619 - closed as not planned/duplicate. This report is scoped narrowly to the focus-stealing/IME-corruption consequence, which those threads did not identify.

Environment

• Claude Code VS Code extension: 2.1.211
• OS: Windows 11 Pro
• VS Code: 1.116.0