EchoSrv: Capture early events (#67977)

* feat: catch any events that were reported before the EchoSrv got initialised

* fix: add events to the new echo service

* chore: update comment

* refactor: use `instanceof` to check if it is a FakeEchoSrv

packages/grafana-runtime/src/services/EchoSrv.ts

@@ -120,6 +120,13 @@ let singletonInstance: EchoSrv;
  * @internal
  */
 export function setEchoSrv(instance: EchoSrv) {
+  // Check if there were any events reported to the FakeEchoSrv (before the main EchoSrv was initialized), and track them
+  if (singletonInstance instanceof FakeEchoSrv) {
+    for (const item of singletonInstance.buffer) {
+      instance.addEvent(item.event, item.meta);
+    }
+  }
+
   singletonInstance = instance;
 }
 
@@ -148,15 +155,15 @@ export const registerEchoBackend = (backend: EchoBackend) => {
 };
 
 export class FakeEchoSrv implements EchoSrv {
-  events: Array<Omit<EchoEvent, 'meta'>> = [];
+  buffer: Array<{ event: Omit<EchoEvent, 'meta'>; meta?: {} | undefined }> = [];
 
   flush(): void {
-    this.events = [];
+    this.buffer = [];
   }
 
   addBackend(backend: EchoBackend): void {}
 
   addEvent<T extends EchoEvent>(event: Omit<T, 'meta'>, meta?: {} | undefined): void {
-    this.events.push(event);
+    this.buffer.push({ event, meta });
   }
 }