transfer local echo state when replacing event entry

e.g. after decryption or remote echo of other relation comes in

src/matrix/room/timeline/Timeline.js

@@ -122,7 +122,9 @@ export class Timeline {
         for (const entry of entries) {
             // this will use the comparator and thus
             // check for equality using the compare method in BaseEntry
-            this._remoteEntries.update(entry);
+            this._remoteEntries.findAndUpdate(entry, (previousEntry, entry) => {
+                entry.transferLocalEchoState(previousEntry);
+            });
         }
     }
 

src/matrix/room/timeline/entries/BaseEventEntry.js

@@ -31,6 +31,11 @@ export class BaseEventEntry extends BaseEntry {
         return this.isRedacting;
     }
 
+    // when replacing an entry, local echo state can be transfered here
+    transferLocalEchoState(oldEntry) {
+        if (oldEntry._pendingRedactions) {
+            this._pendingRedactions = oldEntry._pendingRedactions;
+        }
     }
 
     /**

src/observable/list/SortedArray.js

@@ -41,6 +41,22 @@ export class SortedArray extends BaseObservableList {
         }
     }
 
+    findAndUpdate(newValue, updater) {
+        const index = this.indexOf(newValue);
+        if (index !== -1) {
+            const oldValue = this._items[index];
+            // allow bailing out of sending an emit if updater determined its not needed
+            const params = updater(oldValue, newValue);
+            if (params !== false) {
+                this._items[index] = newValue;
+                this.emitUpdate(index, newValue, params);
+            }
+            // found
+            return true;
+        }
+        return false;
+    }
+
     update(item, updateParams = null) {
         const idx = this.indexOf(item);
         if (idx !== -1) {