✨ Strip incoming changes from update-file response.

Until now, `update-file` always returned a ordered set of change-groups
plus the one created by the ongoing request.

A change-group corresponds to a list of changes commited in a single
update-file (file_change table row).

Including the ongoing request change-group on response with increase
load stated causing considerable amount of memmory pressure.

Since this changes are no longer necessary on frontend side, with this
commit we strip the changes list from the ongoing request change-group,
sending back an empty entry with the increased `revn` number.

backend/src/app/rpc/mutations/files.clj

@@ -332,6 +332,24 @@
       ;; Retrieve and return lagged data
       (retrieve-lagged-changes conn params))))
 
+(def ^:private
+  sql:lagged-changes
+  "select s.id, s.revn, s.file_id,
+          s.session_id, s.changes
+     from file_change as s
+    where s.file_id = ?
+      and s.revn > ?
+    order by s.created_at asc")
+
+(defn- retrieve-lagged-changes
+  [conn params]
+  (->> (db/exec! conn [sql:lagged-changes (:id params) (:revn params)])
+       (into [] (comp (map files/decode-row)
+                      (map (fn [row]
+                             (cond-> row
+                               (= (:revn row) (:revn (:file params)))
+                               (assoc :changes []))))))))
+
 (defn- send-notifications
   [{:keys [msgbus conn] :as cfg} {:keys [file changes session-id] :as params}]
   (let [lchanges (filter library-change? changes)]
@@ -363,17 +381,3 @@
   [conn project-id]
   (:team-id (db/get-by-id conn :project project-id {:columns [:team-id]})))
 
-(def ^:private
-  sql:lagged-changes
-  "select s.id, s.revn, s.file_id,
-          s.session_id, s.changes
-     from file_change as s
-    where s.file_id = ?
-      and s.revn > ?
-    order by s.created_at asc")
-
-(defn- retrieve-lagged-changes
-  [conn params]
-  (->> (db/exec! conn [sql:lagged-changes (:id params) (:revn params)])
-       (mapv files/decode-row)))
-