refactor(acp): split session tests and share rate limiter

src/infra/fixed-window-rate-limit.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+import { createFixedWindowRateLimiter } from "./fixed-window-rate-limit.js";
+
+describe("fixed-window rate limiter", () => {
+  it("blocks after max requests until window reset", () => {
+    let nowMs = 1_000;
+    const limiter = createFixedWindowRateLimiter({
+      maxRequests: 2,
+      windowMs: 1_000,
+      now: () => nowMs,
+    });
+
+    expect(limiter.consume()).toMatchObject({ allowed: true, remaining: 1 });
+    expect(limiter.consume()).toMatchObject({ allowed: true, remaining: 0 });
+    expect(limiter.consume()).toMatchObject({ allowed: false, retryAfterMs: 1_000 });
+
+    nowMs += 1_000;
+    expect(limiter.consume()).toMatchObject({ allowed: true, remaining: 1 });
+  });
+
+  it("supports explicit reset", () => {
+    const limiter = createFixedWindowRateLimiter({
+      maxRequests: 1,
+      windowMs: 10_000,
+    });
+    expect(limiter.consume().allowed).toBe(true);
+    expect(limiter.consume().allowed).toBe(false);
+    limiter.reset();
+    expect(limiter.consume().allowed).toBe(true);
+  });
+});