diff --git a/AGENTS.md b/AGENTS.md
index face4fb7..4f457e24 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -174,9 +174,12 @@ true` ⇒ `history` required; `slashCommands` ≠ `'none'` ⇒ `commands` requir
 
 - Whiteboard (TanStack DB over libSQL): never write to the db inside a collection subscription,
   effect, or render body: it triggers a re-render storm. Writes go in event handlers only.
-- The whiteboard test suite (`packages/extensions/whiteboard/test`) runs in CI only, never locally:
-  not one test, not `--filter`'d. Local gates for whiteboard changes are typecheck/build/lint;
-  behavior evidence comes from a green CI run on the PR.
+- The whiteboard integration tests (`packages/extensions/whiteboard/test/*.it.test.ts` and the
+  browser project) each boot a real Chromium + server; unit tests there are plain node. Its vitest
+  config self-caps `maxWorkers` at 3 off-CI (`localForkCap`), which makes local runs safe: build
+  first (`pnpm turbo run build --filter=@conciv/extension-whiteboard`), then `pnpm exec vitest run`
+  from the package. Never bypass or remove that cap; uncapped runs have saturated a workstation
+  before.
 - The widget bundle must externalize every `@conciv/extension/*` subpath and shared Ark/Solid deps;
   a second bundled copy splits the Solid/Ark context and extension popovers render at 0,0. Guarded
   by the mount-externals build test; don't weaken it.
diff --git a/packages/extensions/whiteboard/vitest.config.ts b/packages/extensions/whiteboard/vitest.config.ts
index db982a71..62e8e608 100644
--- a/packages/extensions/whiteboard/vitest.config.ts
+++ b/packages/extensions/whiteboard/vitest.config.ts
@@ -3,12 +3,21 @@ import {playwright} from '@vitest/browser-playwright'
 import {defineConfig} from 'vitest/config'
 import {ciTest} from '@conciv/vitest-config'
 
+function localForkCap(): {maxWorkers?: number} {
+  if (process.env.GITHUB_ACTIONS !== undefined) return {}
+  const cap = Number(process.env.VITEST_MAX_FORKS)
+  if (Number.isInteger(cap) && cap >= 1) return {}
+  return {maxWorkers: 3}
+}
+
 export default defineConfig({
   test: {
     ...ciTest(),
+    ...localForkCap(),
     projects: [
       {
         test: {
+          ...localForkCap(),
           name: 'whiteboard',
           environment: 'node',
           include: ['test/**/*.test.ts', 'test/**/*.it.test.ts'],
@@ -20,6 +29,7 @@ export default defineConfig({
         plugins: [solid()],
         test: {
           ...ciTest(),
+          ...localForkCap(),
           name: 'whiteboard-browser',
           include: ['test/**/*.browser.test.tsx'],
           testTimeout: 200_000,