- Label editing with 'l' key
- Ctrl+O cycles through filters: default -> user-only -> labeled-only -> all
- Preserve cursor position when toggling filters
- Labels shown at front of node
- Normalize tabs/newlines in content
- extractContent limited to 200 chars for performance
- truncateToWidth on all rendered lines
- Iterative flattenTree to avoid stack overflow
- Linear chain optimization (no indent for single-child chains)
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