[BUG] New conversations fail with "No conversation found with session ID" on Mac desktop app — session focus thrashing in logs

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?

Environment

OS: macOS
App: Claude desktop app (latest, previously reproduced on 2.1.128)
Auth: OAuth (claude.ai account)
MCP servers configured: 14 (mix of remote + local, including Dune, Figma, Gmail, Google Drive, Notion, Slack, Claude in Chrome, plus internal ccd_session/ccd_directory/ccd_session_mgmt)
Working directory at failure: git repo with worktrees under .claude/worktrees/

Description
On the Mac desktop app, every new conversation fails immediately with:
Claude couldn't process that message
Try sending your message again.
No conversation found with session ID: <UUID>
The UUID is different on each attempt, suggesting the client generates a fresh ID per retry but the session is never successfully registered server-side (or the registration fails silently).
Existing conversations continue to work normally. The same account works without issues in the VSCode extension simultaneously, so backend, auth, and network are all fine — this is isolated to the Mac desktop app.
Steps to reproduce

Open Mac desktop app
Click "New Chat"
Send any message
Error appears immediately, no response from Claude

Expected behavior
New conversation is created server-side and Claude responds.
Actual behavior
Error: No conversation found with session ID: <UUID>. Every retry generates a new UUID and fails identically.

What Should Happen?

Answering my question

Error Messages/Logs

Log excerpt — session focus thrashing
The main log shows three local sessions cycling in 1-second intervals, each replacing the previously focused one:
18:19:09 LocalSessions.startShellPty: sessionId=local_cd740ac7-...
18:19:09 LocalSessions.stopShellPty:  sessionId=local_9bf55d47-...
18:19:09 Shell PTY for session local_9bf55d47-... exited (stale — already replaced)
18:19:10 LocalSessions.setFocusedSession: sessionId=null
18:19:10 LocalSessions.setFocusedSession: sessionId=local_4b099755-...
18:19:10 LocalSessions.startShellPty: sessionId=local_4b099755-...
18:19:10 LocalSessions.stopShellPty:  sessionId=local_cd740ac7-...
18:19:10 Shell PTY for session local_cd740ac7-... exited (stale — already replaced)
18:19:11 LocalSessions.setFocusedSession: sessionId=null
18:19:11 LocalSessions.setFocusedSession: sessionId=local_9bf55d47-...
18:19:12 LocalSessions.startShellPty: sessionId=local_9bf55d47-...
18:19:12 Shell PTY for session local_4b099755-... exited (stale — already replaced)
LocalSessions.getPrStateForBranch is called 5 times in rapid succession on every focus switch, which looks like a React render loop driving the focus cycling.

Steps to Reproduce

Steps to reproduce

1. Open Mac desktop app
2. Click "New Chat"
3. Send any message
4. Error appears immediately, no response from Claude

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Version: 2.1.138

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Warp

Additional Information

Workarounds attempted (none successful)

Updated to latest app version
Removed and pruned git worktrees (git worktree remove, git worktree prune)
Full app restart with pkill -9 -f Claude to terminate helper processes
Cleared caches: Cache, Code Cache, GPUCache, Session Storage, claude-code-vm
Sign out → full quit → sign back in
Tested from a fresh directory outside any git project

Additional context

Plugin scan emits warnings (skipped, not blocking): finance:reconciliation and finance:variance-analysis collide with skills/ entries
Coder workspace discovery failed: coder CLI not found on augmented PATH (non-blocking)
Same account works perfectly in the VSCode extension at the same time, ruling out backend/auth/network as the cause

<img width="442" height="252" alt="Image" src="https://github.com/user-attachments/assets/d25f49a2-6365-4ab0-aea4-1010aab5c1d1" />