fix(eve): forward each dev request on a fresh worker connection

.changeset/dev-forward-fresh-connection.md

@@ -0,0 +1,5 @@
+---
+"eve": patch
+---
+
+`eve dev` no longer answers an occasional request with 503 `socket hang up` or `read ECONNRESET` under heavy CPU load. Each request now reaches the dev worker on its own connection instead of a pooled one the worker may have just closed.

packages/eve/scripts/vendor-compiled/env-runner.mjs

@@ -7,6 +7,38 @@ const EVE_SHUTDOWN_SOURCE =
 const ENV_RUNNER_EXIT_SOURCE = 'parentPort?.postMessage({ event: "exit" });';
 const EVE_EXIT_SOURCE = `${ENV_RUNNER_EXIT_SOURCE}\n      parentPort?.close();`;
 
+// env-runner proxies through httpxy's shared keep-alive agent, which never
+// expires idle sockets. A busy parent can then reuse one the worker already
+// closed and fail the forward (#5001). `agent: false` opens a fresh loopback
+// connection per request instead.
+const ENV_RUNNER_FETCH_SOURCE =
+  "return proxyFetch(this._address, this._resolveFetchInput(input), init);";
+const EVE_FETCH_SOURCE =
+  "return proxyFetch(this._address, this._resolveFetchInput(input), init, { agent: false });";
+
+function createFreshWorkerConnectionPlugin() {
+  let patched = false;
+
+  return {
+    name: "eve-env-runner-fresh-worker-connection",
+    transform(code, id) {
+      if (!id.replaceAll("\\", "/").endsWith("/_chunks/common-base-runner.mjs")) {
+        return null;
+      }
+      if (!code.includes(ENV_RUNNER_FETCH_SOURCE)) {
+        throw new Error("env-runner's worker fetch contract changed.");
+      }
+      patched = true;
+      return { code: code.replace(ENV_RUNNER_FETCH_SOURCE, EVE_FETCH_SOURCE), map: null };
+    },
+    buildEnd() {
+      if (!patched) {
+        throw new Error("env-runner's worker fetch was not patched.");
+      }
+    },
+  };
+}
+
 function createGracefulNodeWorkerShutdownPlugin() {
   let patched = false;
 
@@ -41,7 +73,7 @@ function createGracefulNodeWorkerShutdownPlugin() {
 export default {
   packageName: "env-runner",
   compiledPath: "env-runner",
-  plugins: [createGracefulNodeWorkerShutdownPlugin()],
+  plugins: [createFreshWorkerConnectionPlugin(), createGracefulNodeWorkerShutdownPlugin()],
   entries: [
     {
       entry: "dist/_chunks/common-base-runner.mjs",

packages/eve/src/internal/nitro/host/drained-nitro-dev-server.scenario.test.ts

@@ -652,7 +652,7 @@ describe("drained Nitro dev server", () => {
 
   // #5001: a busy parent can hand the next request to a pooled worker socket
   // the worker already closed on its keep-alive timeout.
-  it.fails("forwards a request after the parent stalls past the worker keep-alive timeout", async () => {
+  it("forwards a request after the parent stalls past the worker keep-alive timeout", async () => {
     const appRoot = await mkdtemp(join(tmpdir(), "eve-dev-keep-alive-"));
     const entry = join(appRoot, "worker.mjs");
     await writeFile(entry, 'export default { fetch: () => new Response("worker") };\n', "utf8");