restoreSelectedFolder trusted localStorage blindly: a stale activeFolder
(moved/deleted, or saved while the tree was still empty) left the grid
filtered to a nonexistent folder with a phantom breadcrumb and no way to
recover short of clicking the root breadcrumb. Validate the persisted
path against the freshly loaded tree and reset to root when it is gone;
skip validation when the tree load failed so transient errors don't wipe
the saved location.
Will Miao
3afec0a0be