Collab: a save-all's layout-only sync into a never-entered sheet room left a
doc with layout but zero items; the first entry adopted it and removed every
item on screen. seed() now file-seeds a hollow doc, syncLayoutFromSave skips
never-seeded empty rooms, and the ydoc-boot / sibling-restage paths fall back
to the file. Tree: new tree-hier standalone app + e2e spec covering the
wxwidgets bundle-size and unfocused-selection fixes.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0189z2siCsezE39ugcDKNBMs
