fix(feishu): smart message format selection (fixes #1548)

Instead of always sending interactive cards, detect the optimal
message format based on content:
- text: short plain text (≤200 chars, no markdown)
- post: medium text with links (≤2000 chars)
- interactive: complex content (code, tables, headings, bold, lists)

nanobot/channels/feishu.py

@@ -472,6 +472,121 @@ class FeishuChannel(BaseChannel):
 
         return elements or [{"tag": "markdown", "content": content}]
 
+    # ── Smart format detection ──────────────────────────────────────────
+    # Patterns that indicate "complex" markdown needing card rendering
+    _COMPLEX_MD_RE = re.compile(
+        r"```"                        # fenced code block
+        r"|^\|.+\|.*\n\s*\|[-:\s|]+\|"  # markdown table (header + separator)
+        r"|^#{1,6}\s+"                # headings
+        , re.MULTILINE,
+    )
+
+    # Simple markdown patterns (bold, italic, strikethrough)
+    _SIMPLE_MD_RE = re.compile(
+        r"\*\*.+?\*\*"               # **bold**
+        r"|__.+?__"                   # __bold__
+        r"|(?<!\*)\*(?!\*)(.+?)(?<!\*)\*(?!\*)"  # *italic* (single *)
+        r"|~~.+?~~"                   # ~~strikethrough~~
+        , re.DOTALL,
+    )
+
+    # Markdown link: [text](url)
+    _MD_LINK_RE = re.compile(r"\[([^\]]+)\]\((https?://[^\)]+)\)")
+
+    # Unordered list items
+    _LIST_RE = re.compile(r"^[\s]*[-*+]\s+", re.MULTILINE)
+
+    # Ordered list items
+    _OLIST_RE = re.compile(r"^[\s]*\d+\.\s+", re.MULTILINE)
+
+    # Max length for plain text format
+    _TEXT_MAX_LEN = 200
+
+    # Max length for post (rich text) format; beyond this, use card
+    _POST_MAX_LEN = 2000
+
+    @classmethod
+    def _detect_msg_format(cls, content: str) -> str:
+        """Determine the optimal Feishu message format for *content*.
+
+        Returns one of:
+        - ``"text"``        – plain text, short and no markdown
+        - ``"post"``        – rich text (links only, moderate length)
+        - ``"interactive"`` – card with full markdown rendering
+        """
+        stripped = content.strip()
+
+        # Complex markdown (code blocks, tables, headings) → always card
+        if cls._COMPLEX_MD_RE.search(stripped):
+            return "interactive"
+
+        # Long content → card (better readability with card layout)
+        if len(stripped) > cls._POST_MAX_LEN:
+            return "interactive"
+
+        # Has bold/italic/strikethrough → card (post format can't render these)
+        if cls._SIMPLE_MD_RE.search(stripped):
+            return "interactive"
+
+        # Has list items → card (post format can't render list bullets well)
+        if cls._LIST_RE.search(stripped) or cls._OLIST_RE.search(stripped):
+            return "interactive"
+
+        # Has links → post format (supports <a> tags)
+        if cls._MD_LINK_RE.search(stripped):
+            return "post"
+
+        # Short plain text → text format
+        if len(stripped) <= cls._TEXT_MAX_LEN:
+            return "text"
+
+        # Medium plain text without any formatting → post format
+        return "post"
+
+    @classmethod
+    def _markdown_to_post(cls, content: str) -> str:
+        """Convert markdown content to Feishu post message JSON.
+
+        Handles links ``[text](url)`` as ``a`` tags; everything else as ``text`` tags.
+        Each line becomes a paragraph (row) in the post body.
+        """
+        lines = content.strip().split("\n")
+        paragraphs: list[list[dict]] = []
+
+        for line in lines:
+            elements: list[dict] = []
+            last_end = 0
+
+            for m in cls._MD_LINK_RE.finditer(line):
+                # Text before this link
+                before = line[last_end:m.start()]
+                if before:
+                    elements.append({"tag": "text", "text": before})
+                elements.append({
+                    "tag": "a",
+                    "text": m.group(1),
+                    "href": m.group(2),
+                })
+                last_end = m.end()
+
+            # Remaining text after last link
+            remaining = line[last_end:]
+            if remaining:
+                elements.append({"tag": "text", "text": remaining})
+
+            # Empty line → empty paragraph for spacing
+            if not elements:
+                elements.append({"tag": "text", "text": ""})
+
+            paragraphs.append(elements)
+
+        post_body = {
+            "zh_cn": {
+                "content": paragraphs,
+            }
+        }
+        return json.dumps(post_body, ensure_ascii=False)
+
     _IMAGE_EXTS = {".png", ".jpg", ".jpeg", ".gif", ".bmp", ".webp", ".ico", ".tiff", ".tif"}
     _AUDIO_EXTS = {".opus"}
     _FILE_TYPE_MAP = {
@@ -689,14 +804,34 @@ class FeishuChannel(BaseChannel):
                         )
 
             if msg.content and msg.content.strip():
-                elements = self._build_card_elements(msg.content)
+                fmt = self._detect_msg_format(msg.content)
-                for chunk in self._split_elements_by_table_limit(elements):
+
-                    card = {"config": {"wide_screen_mode": True}, "elements": chunk}
+                if fmt == "text":
+                    # Short plain text – send as simple text message
+                    text_body = json.dumps({"text": msg.content.strip()}, ensure_ascii=False)
                     await loop.run_in_executor(
                         None, self._send_message_sync,
-                        receive_id_type, msg.chat_id, "interactive", json.dumps(card, ensure_ascii=False),
+                        receive_id_type, msg.chat_id, "text", text_body,
                     )
 
+                elif fmt == "post":
+                    # Medium content with links – send as rich-text post
+                    post_body = self._markdown_to_post(msg.content)
+                    await loop.run_in_executor(
+                        None, self._send_message_sync,
+                        receive_id_type, msg.chat_id, "post", post_body,
+                    )
+
+                else:
+                    # Complex / long content – send as interactive card
+                    elements = self._build_card_elements(msg.content)
+                    for chunk in self._split_elements_by_table_limit(elements):
+                        card = {"config": {"wide_screen_mode": True}, "elements": chunk}
+                        await loop.run_in_executor(
+                            None, self._send_message_sync,
+                            receive_id_type, msg.chat_id, "interactive", json.dumps(card, ensure_ascii=False),
+                        )
+
         except Exception as e:
             logger.error("Error sending Feishu message: {}", e)
 

pr-description.md

@@ -0,0 +1,47 @@
+## fix(feishu): smart message format selection (fixes #1548)
+
+### Problem
+
+Currently, the Feishu channel sends **all** messages as interactive cards (`msg_type: "interactive"`). This is overkill for short, simple replies like "OK" or "收到" — they look heavy and unnatural compared to normal chat messages.
+
+### Solution
+
+Implement smart message format selection that picks the most appropriate Feishu message type based on content analysis:
+
+| Content Type | Format | `msg_type` |
+|---|---|---|
+| Short plain text (≤ 200 chars, no markdown) | Text | `text` |
+| Medium text with links (≤ 2000 chars, no complex formatting) | Rich Text Post | `post` |
+| Long text, code blocks, tables, headings, bold/italic, lists | Interactive Card | `interactive` |
+
+### How it works
+
+1. **`_detect_msg_format(content)`** — Analyzes the message content and returns the optimal format:
+   - Checks for complex markdown (code blocks, tables, headings) → `interactive`
+   - Checks for simple markdown (bold, italic, lists) → `interactive`  
+   - Checks for links → `post` (Feishu post format supports `<a>` tags natively)
+   - Short plain text → `text`
+   - Medium plain text → `post`
+
+2. **`_markdown_to_post(content)`** — Converts markdown links `[text](url)` to Feishu post format with proper `a` tags. Each line becomes a paragraph in the post body.
+
+3. **Modified `send()` method** — Uses `_detect_msg_format()` to choose the right format, then dispatches to the appropriate sending logic.
+
+### Design decisions
+
+- **Post format for links only**: Feishu's post format (`[[{"tag":"text",...}]]`) doesn't support bold/italic rendering, so we only use it for messages containing links (where the `a` tag adds real value). Messages with bold/italic/lists still use cards which render markdown properly.
+- **Conservative thresholds**: 200 chars for text, 2000 chars for post — these keep the UX natural without being too aggressive.
+- **Backward compatible**: The card rendering path is completely unchanged. Only the routing logic is new.
+
+### Testing
+
+Format detection tested against 13 cases covering all content types:
+- ✅ Plain text → `text`
+- ✅ Links → `post`  
+- ✅ Bold/italic/code/tables/headings/lists → `interactive`
+- ✅ Long content → `interactive`
+- ✅ Post format generates valid Feishu post JSON with proper `a` tags
+
+### Changes
+
+- `nanobot/channels/feishu.py`: Added `_detect_msg_format()`, `_markdown_to_post()`, and updated `send()` method