[BUG] Slash command menu no longer triggers mid-input in the desktop app (regression; #44447 covered the terminal)

Summary

In the Claude Code view inside Claude Desktop, the slash command menu now only
appears when / is the first character of the input. Typing / anywhere
else produces no suggestions, so skills and slash commands can no longer be
added while composing a longer message.

@ mentions still work anywhere in the input. / does not.

Steps to reproduce

1. Open Claude Desktop and start a Claude Code session.
2. Click into the prompt input.
3. Type /n as the first thing in the input — the menu opens, as expected.
4. Clear the input. Type some text first, e.g. check this repo , then type /n.
5. No menu appears, and the /n is not highlighted as a command.

Same result for a bare /, and for a / typed after an already-recognized
leading command (e.g. /nextjs-seo demo / — only the leading /nextjs-seo is
highlighted).

Expected

Typing / anywhere in the prompt opens the command/skill menu, the same way @
opens the file mention menu anywhere in the prompt.

This is a regression, not a missing feature

Mid-input / was a supported, actively maintained feature:

• Changelog 2.1.20: "Fixed ghost text flickering when typing slash commands mid-input"
• Changelog 2.1.136: "Fixed mid-input slash command autocomplete not working after an initial slash command"
• Commit 870624fc1581a70590e382f263e2972b3f1e56f5: "Added slash command autocomplete support when / appears anywhere in input, not just at the beginning"

Issue #44447 reported this breaking in the terminal (first seen 2.1.92,
still reproducing at 2.1.101 and 2.1.138). That report explicitly noted at the
time: "The desktop app still supports mid-input slash command triggering."
#44447 was auto-closed as stale and locked, so I am filing a new issue as the
bot instructed.

The same regression has now reached the desktop app.

Why it matters

The natural composing order is to write the request first and then attach the
relevant skills. That is no longer possible — the command has to be typed before
the message exists, or the skill has to be named in prose and left for the model
to pick up.

Environment

• Claude Desktop 1.37937.0.0 (Microsoft Store package Claude_1.37937.0.0_x64__pzs8sxrjxfjjc)
• Bundled Claude Code: 2.1.241 (%APPDATA%\Roaming\Claude\claude-code\2.1.241)
• Standalone CLI on the same machine: 2.1.246
• Windows 11 Pro 26200

Note: this is the desktop app's Claude Code view, not the terminal CLI. The UI
appears to be served from claude.ai rather than bundled in app.asar, so the
behavior does not track the local CLI version and cannot be rolled back locally.