Stabilize interrupt handoff UI tests

ui/src/components/IssueProperties.test.tsx

@@ -1,7 +1,7 @@
 // @vitest-environment jsdom
 
-import { act } from "react";
 import type { ComponentProps, ReactNode } from "react";
+import { flushSync } from "react-dom";
 import { createRoot } from "react-dom/client";
 import type {
   ExecutionWorkspace,
@@ -115,6 +115,14 @@ vi.mock("@/components/ui/popover", () => ({
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 (globalThis as any).IS_REACT_ACT_ENVIRONMENT = true;
 
+async function act(callback: () => void | Promise<void>) {
+  let result: void | Promise<void> = undefined;
+  flushSync(() => {
+    result = callback();
+  });
+  await result;
+}
+
 async function flush() {
   await act(async () => {
     await new Promise((resolve) => setTimeout(resolve, 0));

ui/src/components/interrupt-handoff/InterruptHandoffViews.test.tsx

@@ -1,7 +1,7 @@
 // @vitest-environment jsdom
 
-import { act } from "react";
 import type { ReactNode } from "react";
+import { flushSync } from "react-dom";
 import { createRoot, type Root } from "react-dom/client";
 import { afterEach, describe, expect, it, vi } from "vitest";
 import {
@@ -30,6 +30,14 @@ const resolvers: HandoffChipResolvers = {
   currentUserId: "user-board",
 };
 
+async function act(callback: () => void | Promise<void>) {
+  let result: void | Promise<void> = undefined;
+  flushSync(() => {
+    result = callback();
+  });
+  await result;
+}
+
 let activeRoot: Root | null = null;
 let activeHost: HTMLDivElement | null = null;