fix: handle opaque attachment references

server/store/store.go

@@ -4684,8 +4684,8 @@ func (fileMapper) LinkAttachments(tenantID types.TenantID, topic string, msgId t
 			return err
 		}
 		userId := types.ZeroUid
-		if topic != "" && types.GetTopicCat(topic) == types.TopicCatMe {
-			userId = types.ParseUserId(topic)
+		if parsedUserID, ok := fileLinkUserID(topic); ok {
+			userId = parsedUserID
 			topic = ""
 		}
 		return tenantAdp.TenantFileLinkAttachments(tenantID, topic, userId, msgId, fids)
@@ -4693,6 +4693,14 @@ func (fileMapper) LinkAttachments(tenantID types.TenantID, topic string, msgId t
 	return nil
 }
 
+// File link topics may also be opaque retention keys, such as cultivate's cvp prefix.
+func fileLinkUserID(topic string) (types.Uid, bool) {
+	if !strings.HasPrefix(topic, "usr") {
+		return types.ZeroUid, false
+	}
+	return types.ParseUserId(topic), true
+}
+
 func (fileMapper) UserHasAccess(tenantID types.TenantID, fid string, uid types.Uid) (bool, error) {
 	if fid == "" || uid.IsZero() {
 		return false, types.ErrMalformed