Fix entry respawn signal forwarding

Fixes #931

test/fixtures/signal-forwarding/child.ts

@@ -0,0 +1,19 @@
+import http from "node:http";
+
+const server = http.createServer((_, res) => {
+  res.writeHead(200, { "content-type": "text/plain" });
+  res.end("ok");
+});
+
+server.listen(0, "127.0.0.1", () => {
+  const addr = server.address();
+  if (!addr || typeof addr === "string") throw new Error("unexpected address");
+  process.stdout.write(`${addr.port}\n`);
+});
+
+const shutdown = (): void => {
+  server.close(() => process.exit(0));
+};
+
+process.on("SIGTERM", shutdown);
+process.on("SIGINT", shutdown);