feat(notion-writer): add toggle blocks via HTML5 <details>

Multi-line <details>...</details> with optional <summary> emits a Notion
toggle block. Body recurses through _parse_lines so any block type
(lists, code, nested toggles) is supported inside. Depth tracking lets
<details> nest inside <details>. Unclosed <details> at EOF degrades to
plain paragraphs with a stderr warning instead of crashing.

+4 tests, 26 passing total.

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

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

@@ -93,6 +93,49 @@ def _parse_lines(lines: List[str]) -> List[Dict[str, Any]]:
         if not line.strip():
             i += 1
             continue
+
+        # Toggle (HTML5 <details>) — multi-line form, depth-tracked for nesting
+        if line.strip() == '<details>':
+            i += 1
+            # Optional <summary>...</summary> on next non-blank line
+            summary_text = ''
+            while i < len(lines) and not lines[i].strip():
+                i += 1
+            if i < len(lines):
+                summary_match = re.match(r'^\s*<summary>(.*)</summary>\s*$', lines[i])
+                if summary_match:
+                    summary_text = summary_match.group(1)
+                    i += 1
+            # Collect body lines until matching </details>, depth-tracked
+            inner_lines: List[str] = []
+            depth = 1
+            while i < len(lines) and depth > 0:
+                stripped_inner = lines[i].strip()
+                if stripped_inner == '<details>':
+                    depth += 1
+                    inner_lines.append(lines[i])
+                elif stripped_inner == '</details>':
+                    depth -= 1
+                    if depth > 0:
+                        inner_lines.append(lines[i])
+                else:
+                    inner_lines.append(lines[i])
+                i += 1
+            if depth > 0:
+                # Unclosed <details> at EOF — degrade to paragraphs
+                import sys as _sys
+                print("Warning: unclosed <details> at EOF; emitting body as paragraphs",
+                      file=_sys.stderr)
+                if summary_text:
+                    blocks.append(create_paragraph_block(summary_text))
+                for inner in inner_lines:
+                    if inner.strip():
+                        blocks.append(create_paragraph_block(inner))
+                continue
+            children = _parse_lines(inner_lines)
+            blocks.append(create_toggle_block(summary_text, children))
+            continue
+
         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
@@ -328,6 +371,18 @@ def create_callout_block(text: str, alert_type: str) -> Dict[str, Any]:
     }
 
 
+def create_toggle_block(summary_text: str, children_blocks: List[Dict[str, Any]]) -> Dict[str, Any]:
+    """Create a toggle block with summary rich-text and child blocks."""
+    return {
+        "object": "block",
+        "type": "toggle",
+        "toggle": {
+            "rich_text": parse_rich_text(summary_text),
+            "children": children_blocks,
+        },
+    }
+
+
 def create_code_block(code: str, language: str) -> Dict[str, Any]:
     return {
         "object": "block",