fix(tests): migrate forks config to vitest-4 top-level + restore NODE_OPTIONS

Two issues in PR #200 became obvious from the next CI run:

1. **`poolOptions.forks.execArgv` had no effect.** Vitest 4 removed
   `test.poolOptions` entirely — every key under it moved to
   top-level `test.*`. The runner emits this banner on every run:

       DEPRECATED `test.poolOptions` was removed in Vitest 4.
       All previous poolOptions are now top-level options.

   So `test.poolOptions.forks.execArgv: ['--max-old-space-size=8192']`
   was silently ignored. Move it to `test.forks.execArgv` (and
   `test.forks.singleFork`).

2. **NODE_OPTIONS got dropped when the shard step was rewritten.**
   PR #199 added `env: NODE_OPTIONS: --max-old-space-size=8192` to
   the `npm test` step; PR #200 replaced the step with `npx vitest
   run --shard X/2` but did not carry the env-var across. Combined
   with #1, the workers reverted to Node's 4 GB default and shard 2
   (58 files) still OOMs at exactly 4128 MB heap.

Restore NODE_OPTIONS on the workflow step as belt-and-braces — it
gets honored by the parent vitest process, and the migrated config
covers the forked children.

With 8 GB heap × 2 shards × 58 files each, the cumulative state
from ngspice WASM + singletons fits comfortably and the suite
should exit cleanly.

.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

frontend/vitest.config.ts

@@ -23,21 +23,20 @@ export default defineConfig({
     include: ['src/__tests__/**/*.test.ts'],
     testTimeout: 30_000,
     hookTimeout: 30_000,
-    poolOptions: {
+    // 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,
-        // 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'],
     },
-    },
     coverage: {
       provider: 'v8',
       include: [