diff --git a/.github/workflows/frontend-tests.yml b/.github/workflows/frontend-tests.yml
index ff481c6d..c3fb5c09 100644
--- a/.github/workflows/frontend-tests.yml
+++ b/.github/workflows/frontend-tests.yml
@@ -77,11 +77,16 @@ jobs:
 
       - name: Run tests (shard ${{ matrix.shard }}/2)
         run: cd frontend && npx vitest run --shard ${{ matrix.shard }}/2
-        # Heap is also raised inside the vitest config via
-        # poolOptions.forks.execArgv — forks pool ignores
-        # NODE_OPTIONS. With sharding each runner only carries
-        # ~60 test files' worth of leaked WASM/singleton state
-        # so the heap stays well under the ceiling.
+        env:
+          # Belt-and-braces heap raise. The same flag is also set in
+          # vitest.config.ts under `forks.execArgv`, but that path was
+          # under the now-removed `poolOptions.forks` until the latest
+          # commit, and we want the workflow not to depend on the
+          # exact vitest config shape to keep CI green during the
+          # vitest 4 migration. NODE_OPTIONS gets picked up by the
+          # parent vitest process; the forks themselves rely on the
+          # config.
+          NODE_OPTIONS: --max-old-space-size=8192
 
       # Production build smoke — catches Vite/Rollup-only failures that
       # vitest doesn't see (chunk wiring, dynamic imports, manualChunks
diff --git a/frontend/vitest.config.ts b/frontend/vitest.config.ts
index e9f217de..f148e41a 100644
--- a/frontend/vitest.config.ts
+++ b/frontend/vitest.config.ts
@@ -23,20 +23,19 @@ export default defineConfig({
     include: ['src/__tests__/**/*.test.ts'],
     testTimeout: 30_000,
     hookTimeout: 30_000,
-    poolOptions: {
-      forks: {
-        singleFork: false,
-        // Vitest 4's forks pool spawns workers with its own execArgv
-        // and does NOT inherit NODE_OPTIONS from the parent shell, so
-        // raising `--max-old-space-size` via the GHA env-var has no
-        // effect on the actual worker process. The full suite leaks
-        // ngspice WASM modules + singleton state across 117 files and
-        // hits Node's 4 GB default at the end of the run ("Worker
-        // exited unexpectedly / Ineffective mark-compacts near heap
-        // limit"). Bump to 8 GB at the pool level so it actually
-        // takes effect.
-        execArgv: ['--max-old-space-size=8192'],
-      },
+    // Vitest 4 removed `test.poolOptions` — config moved to top-level
+    // `forks` / `threads` / etc. See the deprecation banner the runner
+    // emits: "DEPRECATED test.poolOptions was removed in Vitest 4. All
+    // previous poolOptions are now top-level options."
+    //
+    // Each forked worker also needs its heap cap raised because the
+    // suite leaks state across the 117 test files (ngspice WASM ~30 MB
+    // per init, MixedModeScheduler singleton, zustand stores). Even
+    // sharded (60 files / shard) the leak overflows Node's 4 GB
+    // default; 8 GB plus sharding fits the runner's 16 GB budget.
+    forks: {
+      singleFork: false,
+      execArgv: ['--max-old-space-size=8192'],
     },
     coverage: {
       provider: 'v8',