[BUG] Claude Desktop (Claude Code Desktop) sessions become unresponsive ("Mustering..." forever) while other sessions work fine

Preflight Checklist

• [x] I have searched existing issues 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?

Some sessions in Claude Desktop become permanently unresponsive. The UI shows "Mustering..." indefinitely and never produces a response.

Key observations:

• One session (project ReflexPlusBot) works perfectly in the same app instance
• Another session (project LookUp) is stuck — both the existing session and newly created ones for this project
• Creating a new session for the affected project does not help
• Restarting Claude Desktop (Cmd+Q + killall Claude) does not help
• The issue persists across app restarts
• Internet connection is confirmed working (other sessions respond normally)
• No problematic hooks or MCP configurations in the affected project
• The affected project has a standard .claude/ directory (724KB, one skill, one settings.local.json)

Environment:

• Claude Desktop (Mac, Code mode)
• Opus 4.6 1M model
• Max plan
• macOS (Apple Silicon)
• MCP servers: sequential-thinking, context7, playwright, github, obsidian-mcp-tools
• Bypass permissions mode enabled

What Should Happen?

Claude should answer lol

Error Messages/Logs

No error output — the UI simply shows "Mustering..." with a spinner indefinitely. No crash, no error message. The session appears to hang before any model response is generated.

Steps to Reproduce

1. Open Claude Desktop (Code mode) on macOS
2. Have multiple project sessions open (e.g., Project A and Project B)
3. Project A session works normally — responds to all messages
4. Project B session shows "Mustering..." indefinitely and never responds
5. Create a new session for Project B — also stuck on "Mustering..."
6. Restart Claude Desktop (Cmd+Q) — problem persists for Project B
7. Run killall Claude in Terminal, relaunch — still stuck
8. Project A continues to work fine in the same app instance

Note: This is NOT related to MCP servers, hooks, or project config — the affected project has a minimal .claude/ directory. The issue seems tied to a specific project/session state that survives app restarts.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude 1.2278.0 (e5213f) 2026-04-13T17:49:21.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_