Remote Control: '+' button in mobile app creates 'unknown conversation' instead of showing helpful message

Description

In the Claude mobile app's Code mode, when connected to a local machine via Remote Control, tapping the "+" button to create a new conversation results in an "unknown conversation" error with no useful feedback.

Expected behavior

Either:

1. Disable the "+" button when in Remote Control mode (since the mobile app cannot spawn a new local Claude Code process), or
2. Show a helpful message like "Please start a new claude session on your computer first" instead of silently failing with "unknown conversation"

Current behavior

1. Open Claude mobile app → Code mode
2. Connect to local machine via Remote Control (works fine, can chat in the existing session)
3. Tap "+" to create a new conversation
4. Shows "unknown conversation" — no explanation of why it failed

Why this is confusing

The "+" button appears to be designed for Cloud environments where new sessions can be spawned server-side. But in Remote Control mode, the mobile app is just a bridge to an already-running local process — it cannot create new processes on the user's machine. The UI makes no distinction between these two modes, leading to a confusing experience.

Environment

• Claude Code version: 2.1.81
• Mobile app: Claude iOS app (latest)
• remoteControlAtStartup: true in ~/.claude.json
• macOS Darwin 25.3.0

Screenshots

The "Choose environment" screen shows Remote Control entries alongside Cloud environments, with no visual distinction in capabilities (both show the "+" button).