test: align ui vitest configs with thread policy

test/vitest-scoped-config.test.ts

@@ -163,7 +163,7 @@ describe("scoped vitest configs", () => {
 
   it("defaults channel tests to non-isolated mode", () => {
     expect(defaultChannelsConfig.test?.isolate).toBe(false);
-    expect(defaultChannelsConfig.test?.pool).toBe("forks");
+    expect(defaultChannelsConfig.test?.pool).toBe("threads");
   });
 
   it("keeps the core channel lane limited to non-extension roots", () => {
@@ -199,7 +199,7 @@ describe("scoped vitest configs", () => {
 
   it("defaults extension tests to non-isolated mode", () => {
     expect(defaultExtensionsConfig.test?.isolate).toBe(false);
-    expect(defaultExtensionsConfig.test?.pool).toBe("forks");
+    expect(defaultExtensionsConfig.test?.pool).toBe("threads");
   });
 
   it("normalizes extension channel include patterns relative to the scoped dir", () => {

test/vitest-ui-package-config.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it } from "vitest";
+import uiConfig from "../ui/vitest.config.ts";
+import uiNodeConfig from "../ui/vitest.node.config.ts";
+
+describe("ui package vitest config", () => {
+  it("keeps the standalone ui package on threads and isolate=false", () => {
+    expect(uiConfig.test?.pool).toBe("threads");
+    expect(uiConfig.test?.isolate).toBe(false);
+    expect(uiConfig.test?.projects).toHaveLength(3);
+
+    for (const project of uiConfig.test?.projects ?? []) {
+      expect(project.test?.pool).toBe("threads");
+      expect(project.test?.isolate).toBe(false);
+      expect(project.test?.runner).toBe("../test/non-isolated-runner.ts");
+    }
+  });
+
+  it("keeps the standalone ui node config on threads and isolate=false", () => {
+    expect(uiNodeConfig.test?.pool).toBe("threads");
+    expect(uiNodeConfig.test?.isolate).toBe(false);
+    expect(uiNodeConfig.test?.runner).toBe("../test/non-isolated-runner.ts");
+  });
+});

ui/vitest.config.ts

@@ -1,12 +1,20 @@
 import { playwright } from "@vitest/browser-playwright";
 import { defineConfig, defineProject } from "vitest/config";
-import { jsdomOptimizedDeps } from "../vitest.shared.config.ts";
+import { jsdomOptimizedDeps, resolveDefaultVitestPool } from "../vitest.shared.config.ts";
+
+const sharedUiTestConfig = {
+  isolate: false,
+  pool: resolveDefaultVitestPool(),
+  runner: "../test/non-isolated-runner.ts",
+} as const;
 
 export default defineConfig({
   test: {
+    ...sharedUiTestConfig,
     projects: [
       defineProject({
         test: {
+          ...sharedUiTestConfig,
           deps: jsdomOptimizedDeps,
           name: "unit",
           include: ["src/**/*.test.ts"],
@@ -17,6 +25,7 @@ export default defineConfig({
       }),
       defineProject({
         test: {
+          ...sharedUiTestConfig,
           deps: jsdomOptimizedDeps,
           name: "unit-node",
           include: ["src/**/*.node.test.ts"],
@@ -26,6 +35,7 @@ export default defineConfig({
       }),
       defineProject({
         test: {
+          ...sharedUiTestConfig,
           name: "browser",
           include: ["src/**/*.browser.test.ts"],
           setupFiles: ["./src/test-helpers/lit-warnings.setup.ts"],

ui/vitest.node.config.ts

@@ -1,8 +1,12 @@
 import { defineConfig } from "vitest/config";
+import { resolveDefaultVitestPool } from "../vitest.shared.config.ts";
 
 // Node-only tests for pure logic (no Playwright/browser dependency).
 export default defineConfig({
   test: {
+    isolate: false,
+    pool: resolveDefaultVitestPool(),
+    runner: "../test/non-isolated-runner.ts",
     testTimeout: 120_000,
     include: ["src/**/*.node.test.ts"],
     environment: "node",