test: stabilize gateway ports and timers

src/gateway/gateway.wizard.e2e.test.ts

@@ -1,6 +1,5 @@
 import { randomUUID } from "node:crypto";
 import fs from "node:fs/promises";
-import { createServer } from "node:net";
 import os from "node:os";
 import path from "node:path";
 
@@ -8,52 +7,12 @@ import { describe, expect, it } from "vitest";
 import { WebSocket } from "ws";
 
 import { rawDataToString } from "../infra/ws.js";
+import { getDeterministicFreePortBlock } from "../test-utils/ports.js";
 import { GATEWAY_CLIENT_MODES, GATEWAY_CLIENT_NAMES } from "../utils/message-channel.js";
 import { PROTOCOL_VERSION } from "./protocol/index.js";
 
-async function getFreePort(): Promise<number> {
-  return await new Promise((resolve, reject) => {
-    const srv = createServer();
-    srv.on("error", reject);
-    srv.listen(0, "127.0.0.1", () => {
-      const addr = srv.address();
-      if (!addr || typeof addr === "string") {
-        srv.close();
-        reject(new Error("failed to acquire free port"));
-        return;
-      }
-      const port = addr.port;
-      srv.close((err) => {
-        if (err) reject(err);
-        else resolve(port);
-      });
-    });
-  });
-}
-
-async function isPortFree(port: number): Promise<boolean> {
-  if (!Number.isFinite(port) || port <= 0 || port > 65535) return false;
-  return await new Promise((resolve) => {
-    const srv = createServer();
-    srv.once("error", () => resolve(false));
-    srv.listen(port, "127.0.0.1", () => {
-      srv.close(() => resolve(true));
-    });
-  });
-}
-
 async function getFreeGatewayPort(): Promise<number> {
-  // Gateway uses derived ports (bridge/browser/canvas). Avoid flaky collisions by
-  // ensuring the common derived offsets are free too.
-  for (let attempt = 0; attempt < 25; attempt += 1) {
-    const port = await getFreePort();
-    const candidates = [port, port + 1, port + 2, port + 4];
-    const ok = (await Promise.all(candidates.map((candidate) => isPortFree(candidate)))).every(
-      Boolean,
-    );
-    if (ok) return port;
-  }
-  throw new Error("failed to acquire a free gateway port block");
+  return await getDeterministicFreePortBlock({ offsets: [0, 1, 2, 3, 4] });
 }
 
 async function onceMessage<T = unknown>(