test(app): harden flaky e2e synchronization (#40556)

packages/app/e2e/utils/sse-transport.ts

@@ -247,18 +247,23 @@ export async function installSseTransport<T>(
   return {
     server,
     async waitForConnection(input = {}) {
-      await page.waitForFunction(
+      const connection = await page.waitForFunction(
         (after) => {
           const transport = (window as BrowserTransport).__testSseTransport
           const connections = transport?.command({ type: "connections" }) as SseConnectionRecord[] | undefined
-          return connections?.some((connection) => connection.id > after)
+          return connections?.findLast((connection) => connection.id > after && connection.endedAt === undefined)
         },
         input.after ?? 0,
         { timeout: input.timeout },
       )
-      return (await command<SseConnectionRecord[]>({ type: "connections" })).findLast(
-        (connection) => connection.id > (input.after ?? 0),
-      )!
+      let result: SseConnectionRecord | undefined
+      try {
+        result = await connection.jsonValue()
+      } finally {
+        await connection.dispose()
+      }
+      if (!result) throw new Error("SSE transport connection disappeared while waiting")
+      return result
     },
     send(payload, eventOptions) {
       return command({ type: "send", deliveries: [{ payload, options: eventOptions }], burst: false })