ci: add minimal frontend tests, backend coverage tooling, and fix mypy

frontend/src/lib/backoff.test.ts

@@ -0,0 +1,28 @@
+import { describe, expect, it, vi } from "vitest";
+
+import { createExponentialBackoff } from "./backoff";
+
+describe("createExponentialBackoff", () => {
+  it("increments attempt and clamps delay", () => {
+    vi.spyOn(Math, "random").mockReturnValue(0);
+
+    const backoff = createExponentialBackoff({ baseMs: 100, factor: 2, maxMs: 250, jitter: 0 });
+
+    expect(backoff.attempt()).toBe(0);
+    expect(backoff.nextDelayMs()).toBe(100);
+    expect(backoff.attempt()).toBe(1);
+    expect(backoff.nextDelayMs()).toBe(200);
+    expect(backoff.nextDelayMs()).toBe(250); // capped
+  });
+
+  it("reset brings attempt back to zero", () => {
+    vi.spyOn(Math, "random").mockReturnValue(0);
+
+    const backoff = createExponentialBackoff({ baseMs: 100, jitter: 0 });
+    backoff.nextDelayMs();
+    expect(backoff.attempt()).toBe(1);
+
+    backoff.reset();
+    expect(backoff.attempt()).toBe(0);
+  });
+});