fix(app): hydrate timeline message parents (#35269)

packages/app/e2e/performance/unit/session-tab-switch-probe.test.ts

@@ -0,0 +1,45 @@
+import { expect, test } from "bun:test"
+import type { Page } from "@playwright/test"
+import { measureSessionSwitch } from "../timeline/session-tab-switch-probe"
+
+function testPage(waitFailure?: Error) {
+  const stops: unknown[] = []
+  const page = {
+    evaluate: async (_callback: unknown, input?: unknown) => {
+      if (input) return
+      stops.push(undefined)
+    },
+    waitForFunction: async () => {
+      if (waitFailure) throw waitFailure
+    },
+  } as unknown as Page
+  return { page, stops }
+}
+
+function input(run: () => Promise<void>) {
+  return {
+    destinationIDs: ["destination"],
+    sourceIDs: ["source"],
+    lastID: "destination",
+    href: "/session/destination",
+    switch: run,
+  }
+}
+
+test("stops sampling when the session switch fails", async () => {
+  const failure = new Error("switch failed")
+  const context = testPage()
+
+  await expect(measureSessionSwitch(context.page, input(async () => Promise.reject(failure)))).rejects.toBe(failure)
+
+  expect(context.stops).toHaveLength(1)
+})
+
+test("stops sampling when the stable wait fails", async () => {
+  const failure = new Error("stable wait failed")
+  const context = testPage(failure)
+
+  await expect(measureSessionSwitch(context.page, input(async () => {}))).rejects.toBe(failure)
+
+  expect(context.stops).toHaveLength(1)
+})