[Bug]: Home and Cmd+Left cannot move before a leading skill chip

Area

apps/web, desktop composer

Steps to reproduce

1. Insert a skill chip at the start of an empty composer, for example $claude-review.
2. Type test after it.
3. Move the caret to the end, then press Cmd+Left or Home.

Expected behavior

The caret moves to the beginning of the line, before the chip.

Actual behavior

The caret stops after the chip, before the following text. Plain Left can move before it.

With test $claude-review test, Cmd+Left works. The failure occurs when the chip is first.

Environment

Reported on Windows and reconfirmed during subsequent testing. Current Mac installation: 0.0.41-nightly.20260914.1687; original reproduction build not recorded.

Investigation

The composer source handles arrow navigation across chips explicitly, while macOS Home uses Selection.modify(..., "lineboundary"). This may explain the difference; root cause is not confirmed.

Impact/workaround

Minor editing bug. Use plain Left to reach before the chip.

Screenshot

Caret after the leading chip:

Start in apps/web/src/components/ComposerPromptEditor.tsx, especially the arrow-navigation logic around the cited lines, and compare it with the Home handling that uses Selection.modify("lineboundary"). Reproduce a leading skill chip followed by text, then verify that Home and Cmd+Left place the caret before the chip while ordinary Left continues to work.