Let Element Call widget set session memberships

src/stores/widgets/StopGapWidgetDriver.ts

@@ -144,13 +144,29 @@ export class StopGapWidgetDriver extends WidgetDriver {
             this.allowedCapabilities.add(
                 WidgetEventCapability.forStateEvent(EventDirection.Receive, EventType.RoomEncryption).raw,
             );
+            const clientUserId = MatrixClientPeg.safeGet().getSafeUserId();
             this.allowedCapabilities.add(
-                WidgetEventCapability.forStateEvent(
-                    EventDirection.Send,
-                    "org.matrix.msc3401.call.member",
-                    MatrixClientPeg.safeGet().getSafeUserId(),
-                ).raw,
+                WidgetEventCapability.forStateEvent(EventDirection.Send, "org.matrix.msc3401.call.member", clientUserId)
+                    .raw,
             );
+            const clientDeviceId = MatrixClientPeg.safeGet().getDeviceId();
+            if (clientDeviceId !== null) {
+                this.allowedCapabilities.add(
+                    WidgetEventCapability.forStateEvent(
+                        EventDirection.Send,
+                        "org.matrix.msc3401.call.member",
+                        `_${clientUserId}_${clientDeviceId}`,
+                    ).raw,
+                );
+                // MSC3779 version, with no leading underscore
+                this.allowedCapabilities.add(
+                    WidgetEventCapability.forStateEvent(
+                        EventDirection.Send,
+                        "org.matrix.msc3401.call.member",
+                        `${clientUserId}_${clientDeviceId}`,
+                    ).raw,
+                );
+            }
             this.allowedCapabilities.add(
                 WidgetEventCapability.forStateEvent(EventDirection.Receive, "org.matrix.msc3401.call.member").raw,
             );