Pool host-approved restricted code with scoped and fair graph execution

restricted-execution/service.test.mjs

@@ -5,7 +5,7 @@ import { mkdtemp, writeFile, rm } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { fileURLToPath } from "node:url";
-import { serveRestrictedRegistry } from "./service.mjs";
+import { serveRestrictedRegistry, RestrictedEngineBudget } from "./service.mjs";
 
 const workerd = process.env.QUIXOS_TEST_WORKERD;
 if (!workerd) throw Error("Set QUIXOS_TEST_WORKERD to the pinned engine");
@@ -571,3 +571,28 @@ test("detached digest callbacks cannot use a completed frame or contaminate reus
     await f.close();
   }
 });
+
+test("the shared engine budget evicts idle code families and rejects busy oversubscription", async () => {
+  const engineBudget = new RestrictedEngineBudget(1);
+  const a = await fixture(registry("return request.input;"), { engineBudget });
+  const b = await fixture(
+    registry("return await channel({portId:'read',action:{kind:'state',primitive:'read'},input:null});"),
+    { engineBudget },
+  );
+  try {
+    a.start("first family");
+    assert.equal((await a.receive()).output, "first family");
+    const busy = b.start();
+    const port = await b.receive();
+    assert.equal(a.stats().engines, 0, "Idle foreign code is evicted before allocating another engine");
+    assert.equal(engineBudget.stats().engines, 1);
+    a.start("overload");
+    assert.equal((await a.receive()).error.code, "RESTRICTED_ENGINE_LIMIT");
+    assert.equal(engineBudget.stats().engines, 1);
+    b.send({ kind: "port-result", ...busy, sequence: port.sequence, status: "returned", output: "survived" });
+    assert.equal((await b.receive()).output, "survived");
+  } finally {
+    await Promise.all([a.close(), b.close()]);
+  }
+  assert.equal(engineBudget.stats().engines, 0);
+});