Speed up web vitest suite (~51s -> ~32s): cut per-file import/jsdom overhead

web/vitest.config.js

@@ -2,17 +2,62 @@ import { defineConfig } from 'vitest/config';
 import { svelte } from '@sveltejs/vite-plugin-svelte';
 import { svelteTesting } from '@testing-library/svelte/vite';
 
+// Performance note (web unit-test suite):
+// The suite's cost was dominated by per-file overhead. The same module graph
+// (App, mqtt-store, components, bits-ui, the lucide-svelte icon barrel) was
+// re-imported, re-executed, and the jsdom env re-created for every one of the
+// ~94 spec files. Actual test execution is cheap.
+//
+// The `vmThreads` pool runs each spec file in its own fresh V8 VM context
+// (full per-file isolation, so no cross-file state leakage: the bits-ui
+// teardown fix in tests/setup.js and the clean 0-unhandled / 0-stderr output
+// are preserved) while REUSING the worker's compiled-module cache across
+// files. That collapses the dominant import/transform/environment cost and
+// roughly halves wall-clock without touching a single assertion.
+//
+// Caveat: under `vmThreads` the VM's `window` / `location` globals are
+// non-configurable, so the handful of specs that REPLACE the whole `window`
+// or `location` object (not just define a property on it) cannot run there.
+// They are routed to a standard `forks` project instead. This list only needs
+// to grow if a new spec reassigns the entire `window` / `location` global;
+// such a spec fails loudly under `vmThreads`, never silently.
+const NON_VM_SPECS = [
+  'tests/api-base-derivation.spec.js', // vi.stubGlobal('window', ...)
+  'tests/connection-status.spec.js', // Object.defineProperty(window, 'location', ...)
+  'tests/slash-commands.spec.js', // globalThis.window = { ... }
+];
+
+// Exclude Playwright e2e specs so Vitest only picks up unit tests.
+const BASE_EXCLUDE = ['node_modules', 'dist', 'e2e', 'test-results'];
+
 export default defineConfig({
   // The `svelteTesting` plugin prepends the `browser` resolve condition so
-  // Svelte 5's client-side `mount()` is loaded instead of the SSR stub —
+  // Svelte 5's client-side `mount()` is loaded instead of the SSR stub,
   // required by @testing-library/svelte's `render()` (Batch 4L: a11y scan).
   plugins: [svelte({ hot: !process.env.VITEST }), svelteTesting()],
   test: {
     environment: 'jsdom',
     globals: true,
     setupFiles: ['tests/setup.js'],
-    // Exclude Playwright e2e specs so Vitest only picks up unit tests.
-    include: ['tests/**/*.spec.js'],
-    exclude: ['node_modules', 'dist', 'e2e', 'test-results'],
+    projects: [
+      {
+        extends: true,
+        test: {
+          name: 'vm',
+          pool: 'vmThreads',
+          include: ['tests/**/*.spec.js'],
+          exclude: [...BASE_EXCLUDE, ...NON_VM_SPECS],
+        },
+      },
+      {
+        extends: true,
+        test: {
+          name: 'dom-globals',
+          pool: 'threads',
+          include: NON_VM_SPECS,
+          exclude: BASE_EXCLUDE,
+        },
+      },
+    ],
   },
 });