Visual distinction:
- Populated dimension: dashed cyan ring + [+] indicator
- Empty dimension: subtle gray dashed ring + [○] indicator
- No dimension: plain station (no ring)
Context menu changes:
- "Open dimension" on nodes that have children (zooms in directly)
- "Add dimension" on nodes without children (creates empty zoomable space)
- Removed old "Add child node" option
Add dimension creates an empty children structure on the node with
proper parent metadata. The node immediately shows the [○] indicator
and becomes zoomable. User enters and builds tracks with FAB + branch
handles. Truly recursive metro — any station can contain a world.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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