fix(FN-798): stabilize engine vitest gate pool

Fusion-Task-Id: FN-798

Co-authored-by: Fusion <noreply@runfusion.ai>

packages/engine/vitest.config.ts

@@ -19,7 +19,11 @@ export default defineConfig({
       resolve(__dirname, "../core/src/__test-utils__/vitest-setup.ts"),
     ],
     globalSetup: [resolve(__dirname, "../core/src/__test-utils__/vitest-teardown.ts")],
-    pool: "threads",
+    // Node 24.15.0 on macOS aborts in libuv kqueue when Vitest's
+    // worker-thread pool closes unmanaged file descriptors during this gate.
+    // Fork workers preserve real failure semantics while avoiding the raw
+    // SIGABRT/warning flood; keep worker counts bounded below.
+    pool: "forks",
     maxWorkers,
     minWorkers: 1,
     fileParallelism: true,

scripts/__tests__/engine-vitest-gate-policy.test.mjs

@@ -0,0 +1,64 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const repoRoot = path.resolve(__dirname, "../..");
+
+function read(relativePath) {
+  return readFileSync(path.join(repoRoot, relativePath), "utf8");
+}
+
+function readJson(relativePath) {
+  return JSON.parse(read(relativePath));
+}
+
+test("engine-core gate keeps a Node 24/macOS-safe Vitest pool without hiding warnings", () => {
+  const config = read("packages/engine/vitest.config.ts");
+
+  assert.match(
+    config,
+    /pool:\s*"forks"/,
+    "engine Vitest must use fork workers; thread workers abort with Node 24/macOS libuv kqueue",
+  );
+  assert.doesNotMatch(
+    config,
+    /NODE_NO_WARNINGS/,
+    "the gate must not hide unmanaged-fd warnings by suppressing Node warnings",
+  );
+  assert.match(config, /maxWorkers,/, "worker budgeting must still flow through computeMaxWorkers");
+  assert.match(config, /fileParallelism:\s*true/, "engine-core should preserve file-level parallelism");
+});
+
+test("engine-core remains an explicit allow-listed merge gate", () => {
+  const config = read("packages/engine/vitest.config.ts");
+  const engineCoreBlock = config.match(/name:\s*"engine-core"[\s\S]*?exclude:\s*\[/)?.[0] ?? "";
+  const includeEntries = [...engineCoreBlock.matchAll(/"src\/__tests__\/[^"\n]+\.test\.ts"/g)].map((match) => match[0]);
+
+  assert.equal(new Set(includeEntries).size, includeEntries.length, "engine-core allow-list must not contain duplicates");
+  assert.ok(includeEntries.length >= 18, "engine-core allow-list must not be gutted to avoid the runtime abort");
+  assert.ok(
+    includeEntries.includes('"src/__tests__/workflow-graph-task-runner.test.ts"'),
+    "engine-core must keep workflow graph gate coverage",
+  );
+  assert.ok(
+    includeEntries.includes('"src/__tests__/heartbeat-monitor.test.ts"'),
+    "engine-core must keep heartbeat monitor gate coverage while avoiding FN-779 scope changes",
+  );
+});
+
+test("root and package gate scripts still propagate real Vitest failures", () => {
+  const root = readJson("package.json");
+  const engine = readJson("packages/engine/package.json");
+
+  assert.equal(
+    engine.scripts?.["test:core"],
+    "vitest run --silent=passed-only --reporter=dot --project=engine-core",
+  );
+  assert.match(root.scripts?.["test:gate"] ?? "", /pnpm --filter @fusion\/engine test:core/);
+  assert.doesNotMatch(root.scripts?.["test:gate"] ?? "", /NODE_NO_WARNINGS/);
+  assert.doesNotMatch(root.scripts?.["test"] ?? "", /NODE_NO_WARNINGS/);
+});