refactor(notion-writer): make markdown_to_notion_blocks reentrant

Split the entry function into a public reentrant entry that accepts
either string or List[str], and a private _parse_lines engine that
container detectors will recurse into. No behavior change for existing
callers; all 16 parser tests still pass.

Prep for Phase 3c: callout/toggle/columns/page-mention block coverage.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

custom-skills/32-notion-writer/code/scripts/notion_writer.py

@@ -10,7 +10,7 @@ import re
 import json
 import argparse
 from pathlib import Path
-from typing import Optional, List, Dict, Any
+from typing import Optional, List, Dict, Any, Union
 
 from dotenv import load_dotenv
 from notion_client import Client
@@ -72,32 +72,36 @@ def _split_table_row(line: str) -> List[str]:
     return [cell.strip() for cell in stripped.split('|')]
 
 
-def markdown_to_notion_blocks(markdown_text: str) -> List[Dict[str, Any]]:
-    """Convert markdown text to Notion block objects."""
-    blocks = []
-    lines = markdown_text.split('\n')
-    i = 0
+def markdown_to_notion_blocks(content: Union[str, List[str]]) -> List[Dict[str, Any]]:
+    """Convert markdown text (or pre-split lines) to Notion block objects.
 
+    Reentrant: container detectors recursively call _parse_lines on inner content.
+    """
+    if isinstance(content, str):
+        lines = content.split('\n')
+    else:
+        lines = list(content)
+    return _parse_lines(lines)
+
+
+def _parse_lines(lines: List[str]) -> List[Dict[str, Any]]:
+    """Walk lines and emit Notion blocks. Called recursively by container detectors."""
+    blocks = []
+    i = 0
     while i < len(lines):
         line = lines[i]
-
-        # Skip empty lines
         if not line.strip():
             i += 1
             continue
-
-        # Table (header row + separator + body rows)
         if _is_table_row(line) and i + 1 < len(lines) and TABLE_SEPARATOR_RE.match(lines[i + 1]):
             header_cells = _split_table_row(line)
-            i += 2  # skip separator
+            i += 2
             body_rows: List[List[str]] = []
             while i < len(lines) and _is_table_row(lines[i]):
                 body_rows.append(_split_table_row(lines[i]))
                 i += 1
             blocks.append(create_table_block(header_cells, body_rows))
             continue
-
-        # Headers
         if line.startswith('######'):
             blocks.append(create_heading_block(line[6:].strip(), 3))
         elif line.startswith('#####'):
@@ -110,8 +114,6 @@ def markdown_to_notion_blocks(markdown_text: str) -> List[Dict[str, Any]]:
             blocks.append(create_heading_block(line[2:].strip(), 2))
         elif line.startswith('#'):
             blocks.append(create_heading_block(line[1:].strip(), 1))
-
-        # Code blocks
         elif line.startswith('```'):
             language = line[3:].strip() or 'plain text'
             code_lines = []
@@ -120,40 +122,26 @@ def markdown_to_notion_blocks(markdown_text: str) -> List[Dict[str, Any]]:
                 code_lines.append(lines[i])
                 i += 1
             blocks.append(create_code_block('\n'.join(code_lines), language))
-
-        # Checkbox / Todo (must come before generic bullet match)
         elif line.strip().startswith('- [ ]'):
             text = line.strip()[5:].strip()
             blocks.append(create_todo_block(text, False))
         elif line.strip().startswith('- [x]') or line.strip().startswith('- [X]'):
             text = line.strip()[5:].strip()
             blocks.append(create_todo_block(text, True))
-
-        # Bullet list
         elif line.strip().startswith('- ') or line.strip().startswith('* '):
             text = line.strip()[2:]
             blocks.append(create_bulleted_list_block(text))
-
-        # Numbered list
         elif re.match(r'^\d+\.\s', line.strip()):
             text = re.sub(r'^\d+\.\s', '', line.strip())
             blocks.append(create_numbered_list_block(text))
-
-        # Blockquote
         elif line.startswith('>'):
             text = line[1:].strip()
             blocks.append(create_quote_block(text))
-
-        # Horizontal rule
         elif line.strip() in ['---', '***', '___']:
             blocks.append(create_divider_block())
-
-        # Regular paragraph
         else:
             blocks.append(create_paragraph_block(line))
-
         i += 1
-
     return blocks