Slash command picker no longer triggers on / at the start of a continuation line (only at start of message)

What happened

The / skill/command picker used to open whenever / was typed at the beginning of any line in the composer, which allowed attaching several skills to one message. Now it only opens when / is the very first character of the message. A / at the start of a second or later line stays plain text and no picker appears, so multiple skills can no longer be selected in a single prompt.

Previously working (multiple chips resolved in one message):

make the products page same as this image attached, and the addons to apps.

/design:ux-copy
/design:design-critique
/frontend-design:frontend-design

Now broken — /b on line 2 never opens the picker:

/brainstorming
/b

Steps to reproduce

1. In the composer, type / and pick any skill (e.g. /brainstorming) — chip resolves correctly.
2. Press Enter for a new line.
3. Type / followed by any letter.
4. Expected: picker opens. Actual: stays literal text, no picker.

Environment

• Claude desktop app: 1.34493.1 (updated 2026-08-21)
• Claude Code CLI: 2.1.226 (DISABLE_AUTOUPDATER=1, pinned)
• macOS 26.2, arm64

Ruled out during debugging

• Not project-specific: reproduces in a project with no project skills and no .mcp.json.
• Not skill frontmatter: argument-hint present/absent makes no difference — /brainstorming has none.
• Not plugins: reproduces with all plugins enabled.
• Not the CLI version: reproduces on both 2.1.226 and 2.1.245.

Since the CLI was pinned throughout, the change appears to be on the desktop app side.