Add a promise-based toast when exporting (#2541)

* Add loading and success toasts to export engine command

* Move doExport out to a test utility, test visibility of loading spinner

* Add playwright test for export success toast

* Update Cargo.lock

* Remove loading assertion, it flashes too quickly for Playwright to pick up

src/lang/std/engineConnection.ts

@@ -994,6 +994,10 @@ export class EngineCommandManager {
   engineConnection?: EngineConnection
   defaultPlanes: DefaultPlanes | null = null
   commandLogs: CommandLog[] = []
+  pendingExport?: {
+    resolve: (filename?: string) => void
+    reject: (reason: any) => void
+  }
   _commandLogCallBack: (command: CommandLog[]) => void = () => {}
   private resolveReady = () => {}
   /** Folks should realize that wait for ready does not get called _everytime_
@@ -1150,7 +1154,9 @@ export class EngineCommandManager {
             // because in all other cases we send JSON strings. But in the case of
             // export we send a binary blob.
             // Pass this to our export function.
-            void exportSave(event.data)
+            exportSave(event.data).then(() => {
+              this.pendingExport?.resolve()
+            }, this.pendingExport?.reject)
           } else {
             const message: Models['WebSocketResponse_type'] = JSON.parse(
               event.data
@@ -1548,6 +1554,12 @@ export class EngineCommandManager {
       this.outSequence++
       this.engineConnection?.unreliableSend(command)
       return Promise.resolve()
+    } else if (cmd.type === 'export') {
+      const promise = new Promise((resolve, reject) => {
+        this.pendingExport = { resolve, reject }
+      })
+      this.engineConnection?.send(command)
+      return promise
     }
     if (
       command.cmd.type === 'default_camera_look_at' ||