feat(handler): 添加消息去重功能防止飞书重复投递

实现基于(user_id, content)的消息去重机制，避免飞书在网络抖动时重复投递相同消息。使用10秒时间窗口判断重复消息，超过窗口的旧记录会被自动清理。

bot/handler.py

@@ -25,6 +25,26 @@ _ws_connected: bool = False
 _last_message_time: float = 0.0
 _reconnect_count: int = 0
 
+# Deduplication: drop Feishu re-deliveries by (user_id, content) within a short window.
+# Feishu retries on network hiccups within ~60s using the same payload.
+# We use a 10s window: identical content from the same user within 10s is a re-delivery,
+# not a deliberate repeat (user intentional repeats arrive after the bot has already replied).
+_recent_messages: dict[tuple[str, str], float] = {}  # key: (user_id, content) → timestamp
+_DEDUP_WINDOW = 10.0  # seconds
+
+
+def _is_duplicate(user_id: str, content: str) -> bool:
+    """Return True if this (user, content) pair arrived within the dedup window."""
+    now = time.time()
+    expired = [k for k, ts in _recent_messages.items() if now - ts > _DEDUP_WINDOW]
+    for k in expired:
+        del _recent_messages[k]
+    key = (user_id, content)
+    if key in _recent_messages:
+        return True
+    _recent_messages[key] = now
+    return False
+
 
 def get_ws_status() -> dict[str, Any]:
     """Return WebSocket connection status."""
@@ -79,10 +99,14 @@ def _handle_message(data: P2ImMessageReceiveV1) -> None:
             logger.info("Empty text after stripping, ignoring")
             return
 
-        logger.info("✉  ...%s → %r", open_id[-8:], text[:80])
-
         user_id = open_id or chat_id
 
+        if _is_duplicate(user_id, text):
+            logger.info("Dropping duplicate delivery: user=...%s text=%r", user_id[-8:], text[:60])
+            return
+
+        logger.info("✉  ...%s → %r", open_id[-8:], text[:80])
+
         if _main_loop is None:
             logger.error("Main event loop not set; cannot process message")
             return