diff --git a/packages/studio/tests/e2e/edit-accuracy/case.mjs b/packages/studio/tests/e2e/edit-accuracy/case.mjs
index bc96bd492e..5fb2dc36d3 100644
--- a/packages/studio/tests/e2e/edit-accuracy/case.mjs
+++ b/packages/studio/tests/e2e/edit-accuracy/case.mjs
@@ -19,6 +19,7 @@ import {
   visibleQuad,
 } from "./geometry.mjs";
 import { frameSamplerScript, scoreTeleport, startFrames, stopFrames } from "./teleport.mjs";
+import { terminateWindowsProcessTree } from "../../../../cli/src/utils/processTree.ts";
 
 export const VIEWPORT = { width: 1600, height: 900 };
 const STEPS = 20;
@@ -39,6 +40,12 @@ const up = (port) =>
 const liveServers = new Set();
 /** Signals the server's process group; a group that already exited is not an error. */
 function signalGroup(child, signal) {
+  // Windows has no process groups, so taskkill /T ends the server and its children.
+  if (process.platform === "win32")
+    return void terminateWindowsProcessTree(child.pid).catch((error) => {
+      // taskkill exits 128 when the process is already gone.
+      if (!/status 128$/.test(error.message)) throw error;
+    });
   try {
     process.kill(-child.pid, signal);
   } catch (error) {
@@ -52,16 +59,16 @@ export function killServers() {
 
 const announcedPort = (log) => /http:\/\/localhost:(\d+)/.exec(log.join(""))?.[1];
 
+/** Starts Studio at `port` or, when that is busy, the next free one the CLI binds; returns the port it serves. */
 // fallow-ignore-next-line complexity
 export async function startServer(cli, dir, port, log, home) {
-  // The CLI quietly takes the next free port when asked for a busy one, so only the port it announces counts.
-  if (await up(port)) throw new Error(`port ${port} is already serving`);
   const child = spawn(
     "node",
     [cli, "preview", dir, "--port", String(port), "--no-open", "--foreground", "--force-new"],
     {
       stdio: ["ignore", "pipe", "pipe"],
       detached: true,
+      windowsHide: true,
       // A per-case HOME keeps Studio's undo history inside the case's tmp dir.
       env: {
         ...process.env,
@@ -78,12 +85,8 @@ export async function startServer(cli, dir, port, log, home) {
   for (const deadline = Date.now() + 60_000; Date.now() < deadline; await sleep(200)) {
     if (child.exitCode !== null)
       throw new Error(`studio exited ${child.exitCode}: ${log.join("").slice(-500)}`);
-    const announced = announcedPort(log);
-    if (announced && announced !== String(port)) {
-      await stopServer(child);
-      throw new Error(`studio moved from port ${port} to ${announced}`);
-    }
-    if (announced && (await up(port))) return child;
+    const announced = Number(announcedPort(log));
+    if (announced && (await up(announced))) return { child, port: announced };
   }
   await stopServer(child);
   throw new Error("studio did not start in 60s");
diff --git a/packages/studio/tests/e2e/edit-accuracy/run.mjs b/packages/studio/tests/e2e/edit-accuracy/run.mjs
index 39c9b843a2..5ea5866b33 100644
--- a/packages/studio/tests/e2e/edit-accuracy/run.mjs
+++ b/packages/studio/tests/e2e/edit-accuracy/run.mjs
@@ -112,13 +112,14 @@ async function runOne(spec, browser, decoder, port) {
   let result;
   let server;
   try {
-    server = await startServer(opt.cli, dir, port, log, join(root, "home"));
+    const served = await startServer(opt.cli, dir, port, log, join(root, "home"));
+    server = served.child;
     const { keyRender, ...measured } = await (spec.steps ? runSequence : runCase)({
       browser,
       spec,
       dir,
       files,
-      url: `http://127.0.0.1:${port}/#project/case`,
+      url: `http://127.0.0.1:${served.port}/#project/case`,
       evidence,
     });
     await stopServer(server);
diff --git a/packages/studio/tests/e2e/edit-accuracy/server.test.mjs b/packages/studio/tests/e2e/edit-accuracy/server.test.mjs
new file mode 100644
index 0000000000..daa9e7b805
--- /dev/null
+++ b/packages/studio/tests/e2e/edit-accuracy/server.test.mjs
@@ -0,0 +1,28 @@
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { describe, expect, it } from "vitest";
+import { startServer, stopServer } from "./case.mjs";
+
+// Stands in for the CLI when the asked-for port is busy: it binds another port and announces that one.
+const FAKE_CLI = `
+const server = require("node:http").createServer((req, res) => res.end("[]"));
+server.listen(0, "127.0.0.1", () => console.log("Studio: http://localhost:" + server.address().port));
+`;
+
+describe("starting the bench's Studio server", () => {
+  it("serves on the port the server bound, not the one asked for", async () => {
+    const root = mkdtempSync(join(tmpdir(), "hf-bench-server-"));
+    const cli = join(root, "cli.cjs");
+    writeFileSync(cli, FAKE_CLI);
+    const asked = 1;
+    const { child, port } = await startServer(cli, root, asked, [], root);
+    try {
+      expect(port).not.toBe(asked);
+      expect((await fetch(`http://127.0.0.1:${port}/api/projects`)).ok).toBe(true);
+    } finally {
+      await stopServer(child);
+      rmSync(root, { recursive: true, force: true });
+    }
+  });
+});