Make local e2e reliable in CI: serialize boots, add headless shell

The local project booted its executor web servers with file parallelism on,
the only server-booting project that did. On a CI runner several cold vite
boots at once thrashed past the token-URL wait, timing out stdio-mcp and auth.
Run the files serially like every other server-booting project so the first
boot warms the vite cache. Also install chromium-headless-shell, which the
browser scenarios launch and which does not come with the chromium download.

Author: RhysSullivan

.github/workflows/ci.yml

@@ -92,8 +92,10 @@ jobs:
 
       - run: bun install --frozen-lockfile
 
+      # `chromium` and the new `chromium-headless-shell` ship as separate
+      # downloads; the browser-driven scenarios launch the headless shell.
       - name: Install Playwright Chromium
-        run: bunx playwright install --with-deps chromium
+        run: bunx playwright install --with-deps chromium chromium-headless-shell
 
       # The `local` vitest project is excluded from the default `test` chain
       # (each scenario launches its own server), so run it as its own job.

e2e/vitest.config.ts

@@ -79,14 +79,17 @@ export default defineConfig({
       }),
       // The single-user local app. Each scenario launches its OWN `executor
       // web` via the CLI on a throwaway data dir + an OS-assigned port, so
-      // there is no shared instance and scenarios are independent — file
-      // parallelism is ON. No globalSetup (nothing shared to boot). Only
-      // local/** scenarios. Not part of the default `npm run test` chain; run
-      // with `vitest run --project local`.
+      // there is no shared instance and scenarios are independent. Files run
+      // SERIALLY (like every other server-booting project): a cold `executor
+      // web` boot runs vite's optimizeDeps, and several booting at once on a
+      // CI runner thrash hard enough to blow the token-URL wait. Serial lets
+      // the first boot warm the shared vite cache so the rest come up fast. No
+      // globalSetup (nothing shared to boot). Only local/** scenarios. Not part
+      // of the default `npm run test` chain; run with `vitest run --project local`.
       project("local", {
         include: ["local/**/*.test.ts"],
         globalSetup: [],
-        fileParallelism: true,
+        fileParallelism: false,
         testTimeout: 180_000,
       }),
       // The supervised CLI daemon inside a guest VM, one project per OS. The