test: verify error boundary routes post-mount errors through exit()

Vue's errorHandler (installed after mount) already catches render-time
errors from nested components and routes them through exit(err),
providing error boundary behavior matching Ink's design.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/runtime-tests/integration/lifecycle/error-boundary.test.tsx

@@ -0,0 +1,33 @@
+import { defineComponent, nextTick, shallowRef } from "vue";
+import { expect, test } from "vite-plus/test";
+import { render } from "@vue-tui/testing";
+import { Box, Text } from "@vue-tui/runtime";
+
+test("render-time throw in nested component rejects waitUntilExit", async () => {
+  const trigger = shallowRef(false);
+
+  const Child = defineComponent(() => {
+    return () => {
+      if (trigger.value) throw new Error("child render boom");
+      return <Text>child ok</Text>;
+    };
+  });
+
+  const App = defineComponent(() => {
+    return () => (
+      <Box>
+        <Child />
+      </Box>
+    );
+  });
+
+  const { lastFrame, waitUntilExit } = await render(App);
+  expect(lastFrame()).toContain("child ok");
+
+  // Trigger the error in the child component's render function
+  trigger.value = true;
+  await nextTick();
+
+  // The error should route through errorHandler → exit(err) → rejects waitUntilExit
+  await expect(waitUntilExit()).rejects.toThrow("child render boom");
+});