fix(feishu): add message cache for fetchMessageByID to avoid repeated downloads

- Add messageCache (sync.Map) to FeishuChannel struct
- Cache fetched messages with 30s TTL to avoid re-downloading attachments
  when multiple users reply to the same parent message in a thread
- Cleanup expired entries on read access (no background goroutine needed)

pkg/channels/feishu/feishu_64.go

@@ -19,6 +19,7 @@ import (
 	"strings"
 	"sync"
 	"sync/atomic"
+	"time"
 
 	"github.com/sipeed/picoclaw/pkg/bus"
 	"github.com/sipeed/picoclaw/pkg/channels"
@@ -42,11 +43,17 @@ type FeishuChannel struct {
 	tokenCache *tokenCache // custom cache that supports invalidation
 
 	botOpenID    atomic.Value // stores string; populated lazily for @mention detection
+	messageCache sync.Map     // caches fetched messages (messageID -> *larkim.Message)
 
 	mu     sync.Mutex
 	cancel context.CancelFunc
 }
 
+type cachedMessage struct {
+	msg    *larkim.Message
+	expiry time.Time
+}
+
 func NewFeishuChannel(cfg config.FeishuConfig, bus *bus.MessageBus) (*FeishuChannel, error) {
 	base := channels.NewBaseChannel("feishu", cfg, bus, cfg.AllowFrom,
 		channels.WithGroupTrigger(cfg.GroupTrigger),

pkg/channels/feishu/feishu_reply.go

@@ -14,6 +14,8 @@ import (
 	"github.com/sipeed/picoclaw/pkg/utils"
 )
 
+const messageCacheTTL = 30 * time.Second
+
 const (
 	maxReplyContextLen = 600
 )
@@ -122,6 +124,14 @@ func (c *FeishuChannel) resolveReplyTargetMessageID(ctx context.Context, message
 }
 
 func (c *FeishuChannel) fetchMessageByID(ctx context.Context, messageID string) (*larkim.Message, error) {
+	if cached, ok := c.messageCache.Load(messageID); ok {
+		cm := cached.(*cachedMessage)
+		if time.Now().Before(cm.expiry) {
+			return cm.msg, nil
+		}
+		c.messageCache.Delete(messageID)
+	}
+
 	req := larkim.NewGetMessageReqBuilder().
 		MessageId(messageID).
 		Build()
@@ -138,7 +148,9 @@ func (c *FeishuChannel) fetchMessageByID(ctx context.Context, messageID string)
 		return nil, fmt.Errorf("feishu get message: empty response")
 	}
 
-	return resp.Data.Items[0], nil
+	msg := resp.Data.Items[0]
+	c.messageCache.Store(messageID, &cachedMessage{msg: msg, expiry: time.Now().Add(messageCacheTTL)})
+	return msg, nil
 }
 
 func replyTargetID(message *larkim.EventMessage) string {