fix: Repair _remend, card fallback, parser thematic breaks and headings

CLAUDE.md

@@ -0,0 +1,43 @@
+# Claude Code Quick Reference -- chat-sdk-python
+
+## What is this?
+Python port of Vercel Chat SDK. Multi-platform async chat framework.
+
+## Key Commands
+- `uv sync --group dev` -- install dependencies
+- `uv run pytest tests/ -q` -- run tests
+- `uv run ruff check src/` -- lint
+- `uv run ruff format src/` -- format
+
+## Architecture
+- `src/chat_sdk/chat.py` -- Main Chat orchestrator (handlers, routing, concurrency)
+- `src/chat_sdk/thread.py` -- Thread (streaming, pagination, subscriptions)
+- `src/chat_sdk/channel.py` -- Channel (thread listing, metadata)
+- `src/chat_sdk/types.py` -- All types (Message, Author, Adapter protocol)
+- `src/chat_sdk/adapters/` -- 8 platform adapters
+- `src/chat_sdk/shared/` -- Markdown parser, format converter, streaming renderer
+- `src/chat_sdk/state/` -- Memory, Redis, Postgres backends
+- `tests/` -- 2,477+ tests
+
+## Critical Rules
+1. **Never use `datetime.utcnow()`** -- use `datetime.now(tz=timezone.utc)`
+2. **Never use `asyncio.ensure_future`** -- use `asyncio.get_running_loop().create_task()`
+3. **Never pass raw dicts to `self._chat.process_*`** -- use typed dataclasses (ActionEvent, ReactionEvent, etc.)
+4. **Never use camelCase keys in dispatch dicts** -- always snake_case
+5. **Never use `random.choices` for security tokens** -- use `secrets.token_hex`
+6. **Never import optional deps at module level** -- lazy import inside functions
+7. **Always use `hmac.compare_digest` for signature verification** -- never `==`
+8. **Always use `is not None` for empty-string-valid fields** -- never `or`
+9. **Always validate external URLs before HTTP requests** (SSRF prevention)
+10. **Always check `extend_lock` return value** in processing loops
+
+## Adding a New Adapter
+See docs/ARCHITECTURE.md and CONTRIBUTING.md.
+
+## Upstream Sync
+See docs/UPSTREAM_SYNC.md for TS->Python translation patterns.
+
+## Known Limitations
+- Markdown parser handles common cases but is not full CommonMark
+- StreamingMarkdownRenderer's _remend is simplified vs the npm `remend` library
+- No setext headings, no footnotes, no HTML nodes in the parser

src/chat_sdk/shared/base_format_converter.py

@@ -182,8 +182,16 @@ def render_postable(self, message: PostableMessageInput) -> str:
             if "ast" in message:
                 return self.from_ast(message["ast"])
             if "card" in message:
-                return message.get("fallback_text") or message.get("fallbackText") or ""
+                from chat_sdk.cards import card_to_fallback_text
+
+                return card_to_fallback_text(message["card"])
             if message.get("type") == "card":
+                from chat_sdk.cards import is_card_element
+
+                if is_card_element(message):
+                    from chat_sdk.cards import card_to_fallback_text
+
+                    return card_to_fallback_text(message)
                 return ""
             return str(message)
 
@@ -195,9 +203,8 @@ def render_postable(self, message: PostableMessageInput) -> str:
         if hasattr(message, "ast"):
             return self.from_ast(message.ast)
         if hasattr(message, "card"):
-            fallback = getattr(message, "fallback_text", None)
-            if fallback:
-                return fallback
-            return ""
+            from chat_sdk.cards import card_to_fallback_text
+
+            return card_to_fallback_text(message.card)
 
         return str(message)

src/chat_sdk/shared/markdown_parser.py

@@ -272,7 +272,7 @@ def _parse_inline(text: str) -> list[Content]:
 
 # Patterns used by the block parser
 _HEADING_RE = re.compile(r"^(#{1,6})\s+(.*)")
-_THEMATIC_BREAK_RE = re.compile(r"^(\*{3,}|-{3,}|_{3,})\s*$")
+_THEMATIC_BREAK_RE = re.compile(r"^([-*_]\s*){3,}\s*$")
 _FENCED_CODE_START_RE = re.compile(r"^(`{3,}|~{3,})(.*)")
 _BLOCKQUOTE_RE = re.compile(r"^>\s?(.*)")
 _ORDERED_LIST_RE = re.compile(r"^(\d+)[.)]\s+(.*)")
@@ -452,7 +452,7 @@ def parse_markdown(text: str) -> Root:
         heading_match = _HEADING_RE.match(line)
         if heading_match:
             depth = len(heading_match.group(1))
-            heading_text = heading_match.group(2).strip()
+            heading_text = heading_match.group(2).rstrip().rstrip("#").rstrip()
             children.append(make_heading(depth, _parse_inline(heading_text)))
             i += 1
             continue

src/chat_sdk/shared/streaming_markdown.py

@@ -32,75 +32,115 @@
 # has unclosed constructs).
 
 
+def _strip_fenced_code(text: str) -> str:
+    """Return *text* with content between code fences replaced by empty lines.
+
+    This allows inline-marker counting to ignore literal characters inside
+    fenced code blocks (e.g. ``*`` inside a code block is not an unclosed
+    italic marker).
+    """
+    lines = text.split("\n")
+    result_lines: list[str] = []
+    in_fence = False
+    for line in lines:
+        stripped = line.lstrip()
+        if stripped.startswith("```") or stripped.startswith("~~~"):
+            in_fence = not in_fence
+            result_lines.append("")  # replace fence line itself
+        elif in_fence:
+            result_lines.append("")  # replace content inside fence
+        else:
+            result_lines.append(line)
+    return "\n".join(result_lines)
+
+
 def _remend(text: str) -> str:
-    """Close unclosed inline markdown constructs.
+    """Repair incomplete markdown by closing unclosed inline markers.
 
     This is a simplified Python equivalent of the ``remend`` npm package.
-    It scans for unclosed ``**``, ``*``, ``~~``, `` ` ``, and ``[`` and
-    appends the matching closers.
+    Fixes issues in the previous implementation:
+      - Dead code around ``star_count2`` (removed)
+      - ``~~`` counting confused by ``~~~`` code fences (handled by stripping)
+      - Missing ``__`` / ``_`` (underscore bold/italic) handling (added)
+      - Markers inside code blocks no longer counted as inline markers
+
+    Strategy: count *unescaped* characters for ``*`` and ``_`` (parity-based)
+    outside code fences and code spans.  Count ``~~`` substrings for
+    strikethrough.  Count backtick characters for inline code.
     """
     result = text
 
-    # --- code spans (backtick) ---
-    # Simple heuristic: if the total number of backtick characters is odd,
-    # there must be an unclosed code span -- close it with one backtick.
-    # This is idempotent: after closing, the count becomes even and no
-    # further modification is needed.
-    if result.count("`") % 2 != 0:
+    # --- code fences ---
+    # If inside an unclosed code fence, close it and return immediately.
+    in_code_fence = False
+    for line in result.split("\n"):
+        stripped = line.lstrip()
+        if stripped.startswith("```") or stripped.startswith("~~~"):
+            in_code_fence = not in_code_fence
+
+    if in_code_fence:
+        result += "\n```"
+        return result
+
+    # Strip fenced code blocks so their contents don't affect inline counts.
+    outside_fences = _strip_fenced_code(result)
+
+    # --- inline code backticks ---
+    # Count total backtick characters outside code fences. If odd, one code
+    # span is unclosed -- append a single backtick.
+    backtick_count = outside_fences.count("`")
+    if backtick_count % 2 != 0:
         result += "`"
 
-    # --- bold / italic ---
-    # Count unescaped * sequences
+    # --- bold / italic (* based) ---
+    # Count total unescaped * characters outside code fences. If odd, append
+    # one to make even. This is idempotent: once the count is even, no
+    # further change occurs.
     star_count = 0
     j = 0
-    temp = result
-    while j < len(temp):
-        if temp[j] == "\\":
+    while j < len(outside_fences):
+        if outside_fences[j] == "\\":
             j += 2
             continue
-        if temp[j] == "*":
-            run = 0
-            while j < len(temp) and temp[j] == "*":
-                run += 1
-                j += 1
-            star_count += run
-            continue
+        if outside_fences[j] == "*":
+            star_count += 1
         j += 1
 
     if star_count % 2 != 0:
         result += "*"
-    # After fixing single, check for double
-    star_count2 = 0
-    k = 0
-    temp2 = result
-    while k < len(temp2):
-        if temp2[k] == "\\":
-            k += 2
-            continue
-        if temp2[k] == "*":
-            run = 0
-            while k < len(temp2) and temp2[k] == "*":
-                run += 1
-                k += 1
-            star_count2 += run
+
+    # --- bold / italic (_ based) ---
+    # Same parity approach for underscore markers.
+    under_count = 0
+    j = 0
+    while j < len(outside_fences):
+        if outside_fences[j] == "\\":
+            j += 2
             continue
-        k += 1
+        if outside_fences[j] == "_":
+            under_count += 1
+        j += 1
+
+    if under_count % 2 != 0:
+        result += "_"
 
-    # --- strikethrough ~~  ---
-    tilde_pairs = result.count("~~")
+    # --- strikethrough ~~ ---
+    # Count non-overlapping ``~~`` substrings outside code fences. If odd,
+    # one strikethrough is unclosed -- append ``~~``.
+    tilde_pairs = outside_fences.count("~~")
     if tilde_pairs % 2 != 0:
         result += "~~"
 
     # --- links [text](url) ---
     open_brackets = 0
     m = 0
-    while m < len(result):
-        if result[m] == "\\":
+    while m < len(outside_fences):
+        if outside_fences[m] == "\\":
             m += 2
             continue
-        if result[m] == "[":
+        if outside_fences[m] == "[":
             open_brackets += 1
-        elif result[m] == "]":
+        elif outside_fences[m] == "]":
             open_brackets -= 1
         m += 1
     if open_brackets > 0: