fix(web): move to line edges across composer chips

[Gigioxx]

Home and Cmd+Left stop after a leading composer chip instead of reaching the start of the line.

Use Lexical's RangeSelection.modify for Home/End and macOS Cmd+Left/Right. It already handles inline decorators around the browser's visual line boundary, including Shift-selection and soft wraps. This covers skill, file, citation, and context chips in the shared web/desktop composer. The change removes five lines overall.

Fixes #11892.

Verified in an isolated Chromium client: reproduced the original bug, then passed 62 selection checks and three soft-wrap scenarios. macOS shortcut checks use an overridden platform in Linux Chromium; native macOS and Windows were not run. All 73 focused composer tests, web typecheck, targeted lint, and formatting pass. Runnable browser checks are attached with the evidence.

Same prompt, immediately after Home:

Before	After

Videos press Home, then type BEFORE to show the insertion point: before / after.

Model: GPT-6. Harness: Codex.

Summary by CodeRabbit

• Bug Fixes
  • Home and End keys now navigate to line boundaries on all platforms.
  • On Mac, Command + Left Arrow and Command + Right Arrow now move to the beginning or end of the current line.
  • Improved text selection behavior when using Home, End, and line-boundary keyboard shortcuts in the composer.

[macroscopeapp]

Approvability

Verdict: Approved at 73cbd7a

Macroscope's review found this PR approvable — This is a localized composer keyboard-navigation fix that adjusts line-edge selection behavior and adds macOS Command+Arrow handling. It changes no APIs, schemas, defaults, infrastructure, or sensitive code, and its runtime scope is confined to the existing editor component.

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[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between bf3be75 and 73cbd7a.

📒 Files selected for processing (1)

• apps/web/src/components/ComposerPromptEditor.tsx

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📝 Walkthrough

Walkthrough

The composer keyboard handler now supports Home and End on all platforms, plus Mac Cmd+ArrowLeft and Cmd+ArrowRight. It uses Lexical range selection state and updates line-boundary movement without DOM-to-Lexical selection synchronization.

Changes

Composer navigation

Layer / File(s)	Summary
Line-boundary keyboard handling apps/web/src/components/ComposerPromptEditor.tsx	The handler adds cross-platform Home and End support and Mac Cmd+Arrow line-boundary movement. It reads Lexical range selections and passes a boolean direction to selection.modify. The unused DOM selection import and follow-up synchronization were removed.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: chrisdeeming

Merge Risk: ⚪ Minimal · up to 73cbd

No actionable merge risk remains for this change.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: moving to line edges across composer chips.
Description check	✅ Passed	The description explains the bug, implementation, affected chips, verification, issue reference, and UI changes with before/after screenshots and videos. It does not reproduce the checklist with check…
Linked Issues check	✅ Passed	The change addresses #11892. ComposerHomeEndKeyPlugin now handles Home and End on all platforms. It also handles macOS Cmd+ArrowLeft and Cmd+ArrowRight. The handler uses Lexical $getSelection(), `…
Out of Scope Changes check	✅ Passed	The diff changes only apps/web/src/components/ComposerPromptEditor.tsx. The changes remain within the shared web and desktop composer navigation scope of #11892. No unrelated product behavior is dem…

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