Custom Group membership lost when switching between two accounts (sidebar assignments stored per-origin, not per-account)

What happened

In the Claude Code / Claude Desktop app sidebar, Custom Group membership is silently lost after switching between two logged-in accounts and back.

I have two accounts logged into the desktop app (a personal one and a work one). Sessions organized into Custom Groups under one account fall out of those groups after I switch to the other account and return. The group itself survives, but its assigned sessions are gone and must be re-added by hand every time.

Steps to reproduce

1. Log into two accounts in the desktop app (e.g. personal + work).
2. In Account A, create a Custom Group in the sidebar and assign several sessions to it (Group by: Custom).
3. Switch to Account B and do some work.
4. Switch back to Account A.

Expected: Account A's Custom Group still contains the same sessions.
Actual: The group still exists but is empty / missing the sessions — the group→session assignments were wiped.

Root cause (from inspecting local storage)

The sidebar state — including customGroups and customGroupAssignments — is persisted in the app's Chromium LocalStorage (Local Storage/leveldb) keyed only by origin (https://claude.ai), not by account. Both accounts therefore read and write the same shared customGroupAssignments blob.

On account switch the sidebar re-hydrates with only the active account's sessions and appears to reconcile/prune customGroupAssignments down to the currently-visible session set, then persist the pruned result back to the shared blob. This destroys the other account's assignments (their session UUIDs aren't present in the active account, so they get dropped).

Impact

Custom Groups are effectively unusable for anyone who regularly switches between two accounts — organization is silently destroyed on every switch. There is no user-side workaround, since the shared blob is rewritten on each switch.

Suggested fix

Scope customGroups / customGroupAssignments per account (per logged-in identity), or at minimum stop pruning assignments for sessions that merely aren't visible under the currently active account instead of only those known to be deleted.

Environment

• Claude Desktop app, macOS (Darwin 25.3.0)