fix: 处理撤回消息解密时的500错误

撤回消息会清空content但保留key_version，新增判断跳过此类消息解密，避免整个查询窗口被毒化

server/store/message_crypto.go

@@ -196,7 +196,9 @@ func encryptMessageContent(msg *types.Message) (*types.Message, error) {
 }
 
 func decryptMessageContent(msg *types.Message) error {
-	if msg == nil || msg.KeyVersion <= 0 {
+	// 撤回消息的内容已被清空（recall 会把 head/content 置 NULL，但 content_nonce/key_version 残留），
+	// 此类行没有密文可解，直接放行让上层按已撤回形态下发，否则整个 get data 窗口会被单条撤回消息毒化成 500。
+	if msg == nil || msg.KeyVersion <= 0 || msg.Content == nil {
 		return nil
 	}
 	entry, err := getMessageKey(msg.TenantID, msg.KeyVersion)

server/store/message_crypto_test.go

@@ -82,6 +82,27 @@ func TestMessageCryptoRejectsTampering(t *testing.T) {
 	}
 }
 
+// 撤回消息 content 已被清 NULL，但 recall UPDATE 保留了 content_nonce/key_version；
+// 读路径解密必须跳过此类行，否则单条撤回消息会把整个 get data 窗口毒化成 500（2026-10-08 测试环境实案）。
+func TestMessageCryptoSkipsRecalledContent(t *testing.T) {
+	tenantID := types.TenantID(9004)
+	key := bytes.Repeat([]byte{5}, 32)
+	expires := time.Now().Add(time.Minute)
+	messageKeyCache.Lock()
+	messageKeyCache.items[messageKeyCacheID(tenantID, 0)] = cachedMessageKey{enabled: true, version: 2, key: key, expires: expires}
+	messageKeyCache.items[messageKeyCacheID(tenantID, 2)] = cachedMessageKey{enabled: true, version: 2, key: key, expires: expires}
+	messageKeyCache.Unlock()
+	defer InvalidateMessageEncryptionKeys(tenantID)
+
+	recalled := &types.Message{TenantID: tenantID, Topic: "p2p-recalled", SeqId: 64, KeyVersion: 2, ContentNonce: bytes.Repeat([]byte{1}, 12), Content: nil}
+	if err := decryptMessageContent(recalled); err != nil {
+		t.Fatalf("expected recalled message with nil content to be skipped, got: %v", err)
+	}
+	if recalled.Content != nil {
+		t.Fatalf("nil content should stay nil: %#v", recalled.Content)
+	}
+}
+
 func TestMessageCryptoSearchMatchesDecryptedContent(t *testing.T) {
 	content := map[string]any{"txt": "项目 验收通过", "nested": map[string]any{"title": "日报"}}
 	if !messageContentMatchesSearch(content, "验收") {