Ensure unencrypted fields get exposed by getEffectiveEvent()

Fixes https://github.com/vector-im/element-web/issues/19062

src/models/event.ts

@@ -285,8 +285,28 @@ export class MatrixEvent extends EventEmitter {
      * @returns {IEvent} The event in wire format.
      */
     public getEffectiveEvent(): IEvent {
-        // clearEvent doesn't have all the fields, so we'll copy what we can from this.event
-        return Object.assign({}, this.event, this.clearEvent) as IEvent;
+        const content = Object.assign({}, this.getContent()); // clone for mutation
+
+        if (this.getWireType() === EventType.RoomMessageEncrypted) {
+            // Encrypted events sometimes aren't symmetrical on the `content` so we'll copy
+            // that over too, but only for missing properties. We don't copy over mismatches
+            // between the plain and decrypted copies of `content` because we assume that the
+            // app is relying on the decrypted version, so we want to expose that as a source
+            // of truth here too.
+            for (const [key, value] of Object.entries(this.getWireContent())) {
+                // Skip fields from the encrypted event schema though - we don't want to leak
+                // these.
+                if (["algorithm", "ciphertext", "device_id", "sender_key", "session_id"].includes(key)) {
+                    continue;
+                }
+
+                if (content[key] === undefined) content[key] = value;
+            }
+        }
+
+        // clearEvent doesn't have all the fields, so we'll copy what we can from this.event.
+        // We also copy over our "fixed" content key.
+        return Object.assign({}, this.event, this.clearEvent, { content }) as IEvent;
     }
 
     /**