test: harden daemon lifecycle and e2e reliability across app/cli/server

packages/cli/tests/helpers/network.ts

@@ -0,0 +1,32 @@
+import { createServer } from 'node:net'
+
+/**
+ * Reserve and release an ephemeral TCP port, returning the port number.
+ * Tests can use this to reduce port collision flakiness when spawning daemons.
+ */
+export async function getAvailablePort(): Promise<number> {
+  return new Promise<number>((resolve, reject) => {
+    const server = createServer()
+    server.unref()
+
+    server.once('error', reject)
+    server.listen(0, '127.0.0.1', () => {
+      const address = server.address()
+      if (!address || typeof address === 'string') {
+        server.close(() => {
+          reject(new Error('Failed to resolve an available TCP port'))
+        })
+        return
+      }
+
+      const { port } = address
+      server.close((error) => {
+        if (error) {
+          reject(error)
+          return
+        }
+        resolve(port)
+      })
+    })
+  })
+}