fix: 【不发送】标签在sendProactive路径失效 + 群聊长消息截断防封控

- sendProactive端点新增【不发送】过滤（之前只有主回复路径有）
- sendProactive和主回复路径均增加群聊500字截断+最多2条限制
- 防止第三方平台适配器因过长消息触发封控

Co-Authored-By: Claude <noreply@anthropic.com>

backend/platform-bridge/cmd/main.go

@@ -484,7 +484,7 @@ func startOBv11Readers(router *bridge.PlatformRouter) {
 						if interval <= 0 {
 							interval = 2 * time.Second
 						}
-						// 群聊用更长间隔避免刷屏，且限制最多2条消息
+						// 群聊用更长间隔避免刷屏，限制最多2条消息，单条不超过500字防封控
 						if messageType == "group" {
 							minGroupInterval := 3 * time.Second
 							if interval < minGroupInterval {
@@ -493,6 +493,13 @@ func startOBv11Readers(router *bridge.PlatformRouter) {
 							if len(toSend) > 2 {
 								toSend = toSend[:2]
 							}
+							const maxRunes = 500
+							for i := range toSend {
+								runes := []rune(toSend[i].Content)
+								if len(runes) > maxRunes {
+									toSend[i].Content = string(runes[:maxRunes]) + "\n…(内容过长已截断)"
+								}
+							}
 						}
 						for i, rm := range toSend {
 							if i > 0 && interval > 0 {

backend/platform-bridge/internal/handler/bridge_handler.go

@@ -214,9 +214,36 @@ func (h *BridgeHandler) sendProactive(w http.ResponseWriter, r *http.Request) {
 	content := filterActions(req.Content)
 	content = convertMarkdownPlain(content)
 
+	// 过滤 【不发送】 自我审查标签
+	if strings.Contains(content, "【不发送】") {
+		trimmed := content
+		if len([]rune(trimmed)) > 80 {
+			trimmed = string([]rune(trimmed)[:80]) + "..."
+		}
+		log.Printf("[send-proactive] 昔涟自我审查，跳过发送: %s", trimmed)
+		writeJSON(w, http.StatusOK, map[string]string{"status": "self_censored"})
+		return
+	}
+
 	// 按 \n\n 和 ♪ 拆分为多条消息
 	messages := splitProactiveContent(content)
 
+	// 群聊长消息截断：超过 500 字的单条消息截断，防止封控
+	if msgType == "group" {
+		const maxLen = 500
+		for i, msg := range messages {
+			runes := []rune(msg)
+			if len(runes) > maxLen {
+				messages[i] = string(runes[:maxLen]) + "\n…(内容过长已截断)"
+				log.Printf("[send-proactive] 群聊消息过长截断: %d→%d 字", len(runes), maxLen)
+			}
+		}
+		// 群聊最多2条
+		if len(messages) > 2 {
+			messages = messages[:2]
+		}
+	}
+
 	// Prepend CQ @mention tag if at_user_id is specified
 	atPrefix := ""
 	if req.AtUserID != "" {