fix(qq): use PostGroupMessage for group chat responses

The QQ channel was incorrectly using PostC2CMessage (private message API)
for all messages, including group messages. This caused error code 11255
when replying to @mentions in QQ groups.

Changes:
- Add Peer field to OutboundMessage struct
- Check msg.Peer.Kind in QQ Send method
- Use PostGroupMessage for group messages
- Use PostC2CMessage for direct/private messages
- Pass Peer info when publishing outbound messages

Fixes #1221

pkg/agent/loop.go

@@ -343,6 +343,7 @@ func (al *AgentLoop) Run(ctx context.Context) error {
 							Channel: msg.Channel,
 							ChatID:  msg.ChatID,
 							Content: response,
+							Peer:    msg.Peer,
 						})
 						logger.InfoCF("agent", "Published outbound response",
 							map[string]any{

pkg/bus/types.go

@@ -33,6 +33,7 @@ type OutboundMessage struct {
 	Channel string `json:"channel"`
 	ChatID  string `json:"chat_id"`
 	Content string `json:"content"`
+	Peer    Peer   `json:"peer"` // routing peer (direct, group, etc.)
 }
 
 // MediaPart describes a single media attachment to send.

pkg/channels/qq/qq.go

@@ -126,7 +126,18 @@ func (c *QQChannel) Send(ctx context.Context, msg bus.OutboundMessage) error {
 		Content: msg.Content,
 	}
 
-	// send C2C message
+	// Use appropriate API based on peer type
+	if msg.Peer.Kind == "group" {
+		// send group message
+		_, err := c.api.PostGroupMessage(ctx, msg.ChatID, msgToCreate)
+		if err != nil {
+			logger.ErrorCF("qq", "Failed to send group message", map[string]any{
+				"error": err.Error(),
+			})
+			return fmt.Errorf("qq send: %w", channels.ErrTemporary)
+		}
+	} else {
+		// send C2C (private) message
 		_, err := c.api.PostC2CMessage(ctx, msg.ChatID, msgToCreate)
 		if err != nil {
 			logger.ErrorCF("qq", "Failed to send C2C message", map[string]any{
@@ -134,6 +145,7 @@ func (c *QQChannel) Send(ctx context.Context, msg bus.OutboundMessage) error {
 			})
 			return fmt.Errorf("qq send: %w", channels.ErrTemporary)
 		}
+	}
 
 	return nil
 }