TreeEditor (position/insert/move/remove/duplicate on the BlockTree) and
Warnings (post-write quality checks), plus S18's outline breadth limit
on the 2a Outline/DiviOutlineAbility.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7