fix(desktop): guard composer Enter during IME candidate confirmation

[1525164075]

Summary

• Prevent the desktop chat composer from treating IME candidate-confirmation Enter key events as message submission.
• Handle native composition, Process-key events, and keyCode/which 229 cases.
• Add focused tests for IME Enter handling while preserving normal Enter submit behavior.

Test plan

• npm run test:ui -- src/app/chat/composer/ime-keyboard.test.ts
• npm run test:ui -- src/app/chat/composer
• npm run type-check
• npx eslint src/app/chat/composer/index.tsx src/app/chat/composer/ime-keyboard.ts src/app/chat/composer/ime-keyboard.test.ts

[teknium1]

Thanks for the focused main-composer guard.

Problems

• The same bug class remains in the current user-edit composer: apps/desktop/src/components/assistant-ui/thread/user-edit-composer.tsx:527-577 handles Enter and calls submitEdit() without a composition/229 guard; its editor at :627-652 has no composition handlers.
• apps/desktop/src/app/chat/composer/ime-keyboard.test.ts:7-24 verifies only the pure predicate, not that a candidate-confirmation event cannot reach the production composer submit or trigger-selection paths.

Suggested changes

• Apply the shared guard to the current user-edit composer before its trigger and submit branches, and add its composition lifecycle handling.
• Add a DOM regression that proves 229/Process Enter neither submits nor selects a trigger item.

The linked #43405 discussion identifies #38794 as the canonical IME-fix cluster PR; that does not remove the live main-composer gap at apps/desktop/src/app/chat/composer/index.tsx:364-372.

Automated hermes-sweeper review.

[teknium1]

This verifies only the pure helper. Please add a DOM-level regression that drives the composer keydown path and asserts a 229/Process candidate-confirmation event cannot submit or select a trigger item.

[teknium1]

This fix landed on main via #86760, which consolidated the duplicate PRs for this bug (earliest submission by @satotakumi in #37487; all contributors credited in that PR's body). Closing as the fix is now merged. Thanks for catching it!