Desktop app: custom sidebar session groupings vanished after update (sessions intact, grouping gone)

Environment: Claude desktop app, macOS (Darwin 23.6.0). Version: latest as of 2026-07-19 (exact build unconfirmed).

Summary: After a recent app update, my two custom sidebar session groupings — "Travel Sites" and "Tungsten Sites" — no longer appear. All sessions are still present and openable, but they're now flattened into a single ungrouped list.

This is not a rename. The grouping feature did not move to "Folders" or "Projects." There are no folder chips and no group headers — the grouping is simply gone from the UI.

Steps to reproduce:

1. Update the desktop app
2. Open the sidebar
3. Previously-created session groups are absent

Expected: Custom session groupings persist across app updates.

Actual: Groupings are gone; 50+ sessions are now unorganized in a flat list.

Impact: Loss of organization across a large number of active sessions. Underlying session data appears intact — this is a UI / persisted-grouping regression, not data loss.