chore: import upstream snapshot with attribution

tests/unit/idempotency.test.ts

@@ -0,0 +1,83 @@
+import { describe, it, beforeEach } from "node:test";
+import assert from "node:assert/strict";
+import {
+  getIdempotencyKey,
+  checkIdempotency,
+  saveIdempotency,
+  clearIdempotency,
+  getIdempotencyStats,
+} from "../../src/lib/idempotencyLayer.ts";
+
+describe("Idempotency Layer", () => {
+  beforeEach(() => {
+    clearIdempotency();
+  });
+
+  describe("getIdempotencyKey", () => {
+    it("returns null for null headers", () => {
+      assert.equal(getIdempotencyKey(null), null);
+    });
+
+    it("returns Idempotency-Key header", () => {
+      const headers = new Headers({ "Idempotency-Key": "abc-123" });
+      assert.equal(getIdempotencyKey(headers), "abc-123");
+    });
+
+    it("returns X-Request-Id header", () => {
+      const headers = new Headers({ "X-Request-Id": "req-456" });
+      assert.equal(getIdempotencyKey(headers), "req-456");
+    });
+
+    it("prefers Idempotency-Key over X-Request-Id", () => {
+      const headers = new Headers({
+        "Idempotency-Key": "idemp-1",
+        "X-Request-Id": "req-2",
+      });
+      assert.equal(getIdempotencyKey(headers), "idemp-1");
+    });
+
+    it("supports plain object headers", () => {
+      const headers = { "idempotency-key": "obj-key" };
+      assert.equal(getIdempotencyKey(headers), "obj-key");
+    });
+  });
+
+  describe("checkIdempotency / saveIdempotency", () => {
+    it("returns null for unknown key", () => {
+      assert.equal(checkIdempotency("unknown"), null);
+    });
+
+    it("returns null for null key", () => {
+      assert.equal(checkIdempotency(null), null);
+    });
+
+    it("returns cached response within window", () => {
+      const response = { choices: [{ message: { content: "hello" } }] };
+      saveIdempotency("key-1", response, 200);
+      const result = checkIdempotency("key-1");
+      assert.deepEqual(result, { response, status: 200 });
+    });
+
+    it("returns null after expiry", async () => {
+      const response = { choices: [] };
+      saveIdempotency("key-2", response, 200, 50); // 50ms window
+      await new Promise((r) => setTimeout(r, 100));
+      assert.equal(checkIdempotency("key-2"), null);
+    });
+
+    it("does nothing for null key", async () => {
+      saveIdempotency(null, { data: 1 }, 200);
+      assert.equal((await getIdempotencyStats()).activeKeys, 0);
+    });
+  });
+
+  describe("getIdempotencyStats", () => {
+    it("reports active keys", async () => {
+      saveIdempotency("a", {}, 200);
+      saveIdempotency("b", {}, 200);
+      const stats = await getIdempotencyStats();
+      assert.equal(stats.activeKeys, 2);
+      assert.equal(stats.windowMs, 5000);
+    });
+  });
+});