[BUG] Android app renders slash-command messages without their arguments

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code

### What's Wrong?

In the Android app, a user message that invokes a slash command with arguments renders as the command name only. The argument text is dropped from the displayed message.

Example: `/echo Will this show up in the Android app?` renders on Android as just `/echo` (see `cc-android.png`). The same message in the same session, viewed in the terminal CLI, renders in full as `/echo Will this show up in the Android app?` (see `cc-terminal.png`).

This is display-only, not a transport problem: the arguments still reach the model. `/echo` is a skill that replies with its argument text verbatim, and the reply on Android correctly reads "Will this show up in the Android app?" - so the app received the arguments and simply did not render them in the user bubble.

Impact: when reviewing a session from the phone, there is no way to see what a slash command was actually asked to do. Every invocation of the same command looks identical.

**cc-terminal.png**

**cc-android.png**

### What Should Happen?

The user message should render the full invocation, including arguments - matching the terminal, e.g. `/echo Will this show up in the Android app?`

### Error Messages/Logs

```shell
None - no error is raised; the arguments are silently omitted from the rendered message.
```

### Steps to Reproduce

1. Create a slash command / skill that takes arguments. Minimal example - `~/.claude/skills/echo/SKILL.md`:
```markdown
---
name: echo
description: Reply with the argument text verbatim.
---
Reply with the exact text following `/echo`, verbatim. Nothing added, nothing removed, no preface.
```
2. In the terminal CLI, send: `/echo Will this show up in the Android app?`
3. Confirm the terminal renders the full invocation, arguments included (see `cc-terminal.png`).
4. Open the same session in the Claude Code Android app and look at that user message (see `cc-android.png`).

Expected: `/echo Will this show up in the Android app?`
Actual: `/echo` - the arguments are not rendered.

Note: the arguments are still delivered to the model. The assistant reply shown on Android is the echoed argument text, so only the user-message rendering drops them.

### Claude Model

Opus

### Is this a regression?

I don't know

### Last Working Version

_No response_

### Claude Code Version

2.1.235

### Platform

Anthropic API

### Operating System

Windows

### Terminal/Shell

Windows Terminal

### Additional Information

Android app version: 1.260817.0 (26081700)

Screenshots attached in the What's Wrong section:
- `cc-terminal.png` - terminal CLI rendering the full `/echo ...` invocation
- `cc-android.png` - Android app rendering the same message as `/echo` alone

Reproduce the issue by creating the documented echo skill, sending `/echo Will this show up in the Android app?` in the terminal, and opening the same session in the Android app. Start by tracing how the Android app renders slash-command user messages and compare it with the terminal representation. Done means the Android user bubble displays the command and its arguments while the assistant reply remains unchanged.

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