feat: auto-remove reaction after message processing complete

- _add_reaction now returns reaction_id on success
- Add _remove_reaction_sync and _remove_reaction methods
- Remove reaction when stream ends to clear processing indicator
- Store reaction_id in metadata for later removal

nanobot/channels/feishu.py

@@ -417,7 +417,7 @@ class FeishuChannel(BaseChannel):
             return True
         return self._is_bot_mentioned(message)
 
-    def _add_reaction_sync(self, message_id: str, emoji_type: str) -> None:
+    def _add_reaction_sync(self, message_id: str, emoji_type: str) -> str | None:
         """Sync helper for adding reaction (runs in thread pool)."""
         from lark_oapi.api.im.v1 import CreateMessageReactionRequest, CreateMessageReactionRequestBody, Emoji
         try:
@@ -433,22 +433,54 @@ class FeishuChannel(BaseChannel):
 
             if not response.success():
                 logger.warning("Failed to add reaction: code={}, msg={}", response.code, response.msg)
+                return None
             else:
                 logger.debug("Added {} reaction to message {}", emoji_type, message_id)
+                return response.data.reaction_id if response.data else None
         except Exception as e:
             logger.warning("Error adding reaction: {}", e)
+            return None
 
-    async def _add_reaction(self, message_id: str, emoji_type: str = "THUMBSUP") -> None:
+    async def _add_reaction(self, message_id: str, emoji_type: str = "THUMBSUP") -> str | None:
         """
         Add a reaction emoji to a message (non-blocking).
 
         Common emoji types: THUMBSUP, OK, EYES, DONE, OnIt, HEART
         """
         if not self._client:
+            return None
+
+        loop = asyncio.get_running_loop()
+        return await loop.run_in_executor(None, self._add_reaction_sync, message_id, emoji_type)
+
+    def _remove_reaction_sync(self, message_id: str, reaction_id: str) -> None:
+        """Sync helper for removing reaction (runs in thread pool)."""
+        from lark_oapi.api.im.v1 import DeleteMessageReactionRequest
+        try:
+            request = DeleteMessageReactionRequest.builder() \
+                .message_id(message_id) \
+                .reaction_id(reaction_id) \
+                .build()
+
+            response = self._client.im.v1.message_reaction.delete(request)
+            if response.success():
+                logger.debug("Removed reaction {} from message {}", reaction_id, message_id)
+            else:
+                logger.debug("Failed to remove reaction: code={}, msg={}", response.code, response.msg)
+        except Exception as e:
+            logger.debug("Error removing reaction: {}", e)
+
+    async def _remove_reaction(self, message_id: str, reaction_id: str) -> None:
+        """
+        Remove a reaction emoji from a message (non-blocking).
+
+        Used to clear the "processing" indicator after bot replies.
+        """
+        if not self._client or not reaction_id:
             return
 
         loop = asyncio.get_running_loop()
-        await loop.run_in_executor(None, self._add_reaction_sync, message_id, emoji_type)
+        await loop.run_in_executor(None, self._remove_reaction_sync, message_id, reaction_id)
 
     # Regex to match markdown tables (header + separator + data rows)
     _TABLE_RE = re.compile(
@@ -1046,6 +1078,9 @@ class FeishuChannel(BaseChannel):
 
         # --- stream end: final update or fallback ---
         if meta.get("_stream_end"):
+            if (message_id := meta.get("message_id")) and (reaction_id := meta.get("reaction_id")):
+                await self._remove_reaction(message_id, reaction_id)
+
             buf = self._stream_bufs.pop(chat_id, None)
             if not buf or not buf.text:
                 return
@@ -1227,7 +1262,7 @@ class FeishuChannel(BaseChannel):
                 return
 
             # Add reaction
-            await self._add_reaction(message_id, self.config.react_emoji)
+            reaction_id = await self._add_reaction(message_id, self.config.react_emoji)
 
             # Parse content
             content_parts = []
@@ -1305,6 +1340,7 @@ class FeishuChannel(BaseChannel):
                 media=media_paths,
                 metadata={
                     "message_id": message_id,
+                    "reaction_id": reaction_id,
                     "chat_type": chat_type,
                     "msg_type": msg_type,
                     "parent_id": parent_id,