## Why
Opening a saved side chat waits for thread resume and history loading. Keep the chooser usable during that work and switch conversations only if the user still wants to open the chat.
## What changed
- Prepare saved chats in the background and show opening, waiting, and retry states in the sidebar. Allow cancellation and keep only the latest queued destination, with at most two preparations in flight.
- Ignore stale completions after navigation, archiving, disconnects, or backend changes, and release unclaimed subscriptions on their original connection.
- Preserve live events, settings, read receipts, and pending approvals received during loading. Anchor paginated history to the resumed snapshot to avoid overlap with live events.
- Carry held-key suppression across conversation switches.
## Testing
Add regression tests for retry and supersession, cancellation, stale completions, subscription cleanup, live updates during attachment, and held keys, plus snapshots for waiting and retry rows.
GitOrigin-RevId: 2c7d94482078f16895049ce79b242d3eb0d92f40
Felipe Coury
37103d7f01