Folder tree expand/collapse state resets after a move

[ChrisonSimtian]

Usage Information

• BitwardenSharp dbbf4df (develop)
• .NET SDK 10.0.400, net10.0
• Avalonia 12.1.1
• Bitwarden CLI 2026.7.0
• macOS 26.5.2 (arm64)

Description

Collapsing folders in the tree is undone by any folder operation. After dragging an item onto a
folder, every node is expanded again, so a tree that has been tidied down to a few branches has to
be re-collapsed after every move.

On a vault with nested folders (Homelab/Proxmox, Homelab/Synology, …) this makes repeated
moves tedious, which is exactly the workflow drag-and-drop exists to support.

Reproduction Steps

1. Unlock and open the vault browser.
2. Collapse one or more folder nodes in the left-hand tree.
3. Drag any item from the middle list onto a folder in the tree.
4. Observe the tree once the move completes.

Expected Behavior

Nodes that were collapsed stay collapsed. The operation changed one item's folder; it did not
change how the tree is being viewed.

Actual Behavior

Every node is expanded. The previous expand/collapse state is gone.

Regression?

No — present since folder management was added (422baed).

Known Workarounds

None. Re-collapse manually after each move.

Notes — where to look

FolderNode already has a two-way–bound IsExpanded, so the binding is not the problem. The
state is lost because VaultViewModel.RebuildFolderTree() calls Folders.Clear() and constructs
brand-new FolderNode instances on every load; the expansion state lives on the objects that were
just discarded.

Two candidate fixes:

• Capture the expanded paths before the rebuild and reapply them after (cheap, keeps the rebuild).
• Reconcile the existing tree in place rather than rebuilding it (better, more work) — which would
  also fix the selection flicker and help with Item list still shows an item after it is moved out of the viewed folder #3.

Related: #3, #4.