test(e2e): a localhost connect the machine dropped is tried again on the test side

On a Windows host a burst of test traffic can drop a loopback connect now and then (every port,
any program — measured on the dev desktop). The browser resends it and only waits; Node (libuv)
sends a loopback SYN once and fails at ~300 ms with "connect ETIMEDOUT". `e2e/retryConnect.ts` wraps
Playwright's request context so that one error is tried again (0.5 / 1 / 2 / 4 / 8 s, the system's
own retry waits) while every other failure goes straight to the test; global.setup's health check,
login and /api/me and speed.measure's share probe go through it. Unit-tested; e2e 61/61.

frontend/src/lib/e2eRetryConnect.test.ts

@@ -0,0 +1,41 @@
+// The e2e suite's request wrapper (e2e/retryConnect.ts): a connect that never came about is tried
+// again, as every TCP stack would; any other failure, or an answer, goes straight to the test.
+import { describe, expect, it, vi } from "vitest";
+import { retryConnect } from "../../e2e/retryConnect";
+
+const noConnection = () => new Error("apiRequestContext.get: connect ETIMEDOUT 127.0.0.1:8080");
+
+describe("retryConnect", () => {
+  it("tries a connect that timed out again, and hands back the answer that came", async () => {
+    vi.useFakeTimers();
+    const get = vi
+      .fn()
+      .mockRejectedValueOnce(noConnection())
+      .mockRejectedValueOnce(noConnection())
+      .mockResolvedValue("ok");
+    const api = retryConnect({ get });
+    const answer = api.get("/healthz");
+    await vi.runAllTimersAsync();
+    await expect(answer).resolves.toBe("ok");
+    expect(get).toHaveBeenCalledTimes(3);
+    expect(get).toHaveBeenLastCalledWith("/healthz");
+    vi.useRealTimers();
+  });
+
+  it("passes any other failure straight on, untried", async () => {
+    const post = vi.fn().mockRejectedValue(new Error("read ECONNRESET"));
+    await expect(retryConnect({ post }).post("/auth/password-login")).rejects.toThrow("ECONNRESET");
+    expect(post).toHaveBeenCalledTimes(1);
+  });
+
+  it("gives up after its last wait, with the connect error", async () => {
+    vi.useFakeTimers();
+    const get = vi.fn().mockRejectedValue(noConnection());
+    const answer = retryConnect({ get }).get("/api/me");
+    const settled = expect(answer).rejects.toThrow("ETIMEDOUT");
+    await vi.runAllTimersAsync();
+    await settled;
+    expect(get).toHaveBeenCalledTimes(6); // the first try and five more
+    vi.useRealTimers();
+  });
+});