fix(test): cap native worker pools for serial Vitest

scripts/run-vitest.mjs

@@ -40,12 +40,42 @@ export function resolveVitestNoOutputTimeoutMs(env = process.env) {
 
 export function resolveVitestSpawnParams(env = process.env, platform = process.platform) {
   return {
-    env,
+    env: resolveVitestSpawnEnv(env),
     detached: shouldUseDetachedVitestProcessGroup(platform),
     stdio: ["inherit", "pipe", "pipe"],
   };
 }
 
+export function resolveVitestSpawnEnv(env = process.env) {
+  if (!shouldApplyNativeWorkerBudget(env)) {
+    return env;
+  }
+
+  const nativeWorkerCount = String(resolveNativeWorkerCount(env));
+  return {
+    ...env,
+    RAYON_NUM_THREADS: env.RAYON_NUM_THREADS?.trim() || nativeWorkerCount,
+    TOKIO_WORKER_THREADS: env.TOKIO_WORKER_THREADS?.trim() || nativeWorkerCount,
+  };
+}
+
+function shouldApplyNativeWorkerBudget(env) {
+  if (env.RAYON_NUM_THREADS?.trim() && env.TOKIO_WORKER_THREADS?.trim()) {
+    return false;
+  }
+  return (
+    env.OPENCLAW_TEST_PROJECTS_SERIAL === "1" || resolveExplicitVitestWorkerBudget(env) !== null
+  );
+}
+
+function resolveNativeWorkerCount(env) {
+  return Math.min(resolveExplicitVitestWorkerBudget(env) ?? 1, 4);
+}
+
+function resolveExplicitVitestWorkerBudget(env) {
+  return parsePositiveInt(env.OPENCLAW_VITEST_MAX_WORKERS ?? env.OPENCLAW_TEST_WORKERS);
+}
+
 export function shouldSuppressVitestStderrLine(line) {
   return SUPPRESSED_VITEST_STDERR_PATTERNS.some((pattern) => line.includes(pattern));
 }

scripts/test-projects.test-support.mjs

@@ -230,7 +230,11 @@ const TOOLING_SOURCE_TEST_TARGETS = new Map([
   ["scripts/lib/vitest-local-scheduling.mjs", ["test/scripts/vitest-local-scheduling.test.ts"]],
   [
     "scripts/run-vitest.mjs",
-    ["test/scripts/test-projects.test.ts", "test/scripts/vitest-local-scheduling.test.ts"],
+    [
+      "test/scripts/run-vitest.test.ts",
+      "test/scripts/test-projects.test.ts",
+      "test/scripts/vitest-local-scheduling.test.ts",
+    ],
   ],
   ["scripts/run-oxlint.mjs", ["test/scripts/run-oxlint.test.ts"]],
   ["scripts/test-extension-batch.mjs", ["test/scripts/test-extension.test.ts"]],

test/scripts/run-vitest.test.ts

@@ -58,6 +58,40 @@ describe("scripts/run-vitest", () => {
     });
   });
 
+  it("caps native Rust worker pools for serial Vitest runs", () => {
+    expect(
+      resolveVitestSpawnParams(
+        {
+          OPENCLAW_TEST_PROJECTS_SERIAL: "1",
+          PATH: "/usr/bin",
+        },
+        "darwin",
+      ).env,
+    ).toMatchObject({
+      OPENCLAW_TEST_PROJECTS_SERIAL: "1",
+      RAYON_NUM_THREADS: "1",
+      TOKIO_WORKER_THREADS: "1",
+    });
+  });
+
+  it("keeps explicit native Rust worker pool settings", () => {
+    expect(
+      resolveVitestSpawnParams(
+        {
+          OPENCLAW_VITEST_MAX_WORKERS: "2",
+          PATH: "/usr/bin",
+          RAYON_NUM_THREADS: "8",
+          TOKIO_WORKER_THREADS: "6",
+        },
+        "darwin",
+      ).env,
+    ).toMatchObject({
+      OPENCLAW_VITEST_MAX_WORKERS: "2",
+      RAYON_NUM_THREADS: "8",
+      TOKIO_WORKER_THREADS: "6",
+    });
+  });
+
   it("suppresses rolldown plugin timing noise while keeping other stderr intact", () => {
     expect(
       shouldSuppressVitestStderrLine(