[BUG] Desktop app: Forks don't inherit the parent session's sidebar group

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?

In the macOS desktop app I keep sessions in custom sidebar groups. Forking a session that's in a group produces Session name (fork) in Ungrouped, not in the parent's group, so I have to drag it back every time.

What Should Happen?

A fork should inherit its parent's group — it's a direct child and belongs alongside it. If the parent is ungrouped, the fork stays in Ungrouped too.

Error Messages/Logs

None — this is UI placement behavior, no error.

Steps to Reproduce

1. In the desktop app, put a session into a custom sidebar group
2. Fork that session (/branch, or the sidebar Fork action)
3. Look at the sidebar — the new … (fork) appears under Ungrouped, not in the parent's group

Claude Model

Opus (not model-dependent)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.217 (desktop app)

Platform

Claude Max subscription

Operating System

macOS 26.5.1

Terminal/Shell

N/A — macOS desktop app (Electron shell 1.24012.1)

Additional Information

Related but distinct:

• #73390 — new sessions also default to Ungrouped. Same family, but that's new sessions, not a fork losing a group it already has
• #78638 — the TUI --resume picker doesn't show the root→branch hierarchy. Different surface, different grouping concept

Not model-dependent.