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/test_parser.py

@@ -211,6 +211,75 @@ def test_callout_unknown_falls_through():
     _assert("[!BOGUS]" in quote_text, "[!BOGUS] marker preserved in quote text")
 
 
+def test_toggle_basic():
+    md = "<details>\n<summary>Click to expand</summary>\n\nInner paragraph.\n</details>"
+    blocks = markdown_to_notion_blocks(md)
+    _assert(len(blocks) == 1, "one block emitted")
+    _assert(blocks[0]["type"] == "toggle", "block type is toggle")
+    summary_text = blocks[0]["toggle"]["rich_text"][0]["text"]["content"]
+    _assert(summary_text == "Click to expand", "summary text preserved")
+    children = blocks[0]["toggle"]["children"]
+    _assert(len(children) == 1, "one child block")
+    _assert(children[0]["type"] == "paragraph", "child is paragraph")
+
+
+def test_toggle_nested_blocks():
+    """Toggle body can hold any block type via _parse_lines recursion."""
+    md = """<details>
+<summary>Debug log</summary>
+
+- step one
+- step two
+
+```python
+print("hello")
+```
+</details>"""
+    blocks = markdown_to_notion_blocks(md)
+    _assert(blocks[0]["type"] == "toggle", "block is toggle")
+    children = blocks[0]["toggle"]["children"]
+    types = [c["type"] for c in children]
+    _assert("bulleted_list_item" in types, "list child preserved")
+    _assert("code" in types, "code child preserved")
+    code_block = next(c for c in children if c["type"] == "code")
+    _assert(code_block["code"]["language"] == "python", "code language preserved")
+
+
+def test_toggle_nested_toggle():
+    """details_depth tracking allows <details> inside <details>."""
+    md = """<details>
+<summary>outer</summary>
+
+<details>
+<summary>inner</summary>
+
+inner content
+</details>
+</details>"""
+    blocks = markdown_to_notion_blocks(md)
+    _assert(blocks[0]["type"] == "toggle", "outer block is toggle")
+    outer_children = blocks[0]["toggle"]["children"]
+    _assert(len(outer_children) == 1, "outer has exactly one child")
+    _assert(outer_children[0]["type"] == "toggle", "outer child is also toggle")
+    inner_summary = outer_children[0]["toggle"]["rich_text"][0]["text"]["content"]
+    _assert(inner_summary == "inner", "inner summary preserved")
+
+
+def test_toggle_unclosed_falls_through():
+    """Missing </details> at EOF degrades to paragraphs, no crash."""
+    md = "<details>\n<summary>oops</summary>\n\nbody line"
+    blocks = markdown_to_notion_blocks(md)
+    types = [b["type"] for b in blocks]
+    _assert("toggle" not in types, "no toggle emitted on unclosed <details>")
+    paragraph_texts = [
+        b["paragraph"]["rich_text"][0]["text"]["content"]
+        for b in blocks if b["type"] == "paragraph"
+    ]
+    joined = " ".join(paragraph_texts)
+    _assert("oops" in joined, "summary preserved as paragraph")
+    _assert("body line" in joined, "body preserved as paragraph")
+
+
 def test_rich_text_anchor_link_becomes_bold():
     """TOC-style fragment links must not be sent as Notion link annotations."""
     spans = parse_rich_text("see [Section A](#section-a) below")
@@ -266,6 +335,10 @@ def run_all():
         test_callout_warning,
         test_callout_caution,
         test_callout_unknown_falls_through,
+        test_toggle_basic,
+        test_toggle_nested_blocks,
+        test_toggle_nested_toggle,
+        test_toggle_unclosed_falls_through,
         test_rich_text_anchor_link_becomes_bold,
         test_rich_text_relative_link_becomes_plain,
         test_rich_text_absolute_link_preserved,