Pandoc-style ::: columns / ::: column / ::: blocks emit a Notion
column_list with column children. Each column's body recurses through
_parse_lines so any block type (lists, code, nested columns) works
inside. Single-column wrappers degrade to plain paragraphs because
Notion requires at least two columns.
Single-depth-counter design: depth=1 on enter, increments on `::: columns`
or `::: column`, decrements on `:::`. depth=0 closes the wrapper.
+3 tests, 29 passing total.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Andrew Yim
0421a65327