Add Playwright E2E test suite (25 tests across 4 specs)

- playwright.config.ts: headless CI setup with JSON/HTML reporters
- e2e/global-setup.ts: app reachability check before tests
- e2e/auth.spec.ts: 6 auth tests (sign-in, session, protected routes)
- e2e/compare.spec.ts: 8 API tests (validation, SSE flow, DB persistence)
- e2e/comparisons.spec.ts: 6 CRUD tests (list, detail, 404, view counts)
- e2e/user.spec.ts: 5 user tests (stats, pagination, session binding)
- e2e/helpers.ts: shared SSE parsing, auth, URL resolution utilities
- e2e/README.md: setup and run instructions
- AGENTS.md: updated with LLM provider notes and testing docs
- .gitignore: added playwright report/result directories
- package.json: added @playwright/test and test:e2e scripts

e2e/comparisons.spec.ts

@@ -0,0 +1,95 @@
+import { test, expect } from "@playwright/test";
+import { resolveUrl, getSessionCookie, parseSSEStream, lastSSEOfType } from "./helpers";
+
+/**
+ * E2E tests for comparison list and detail views.
+ * Covers: /api/comparisons/[slug], /api/user/comparisons
+ */
+test.describe("Comparisons", () => {
+  let cookie: string;
+  let testSlug: string;
+
+  test.beforeAll(async ({ page }) => {
+    cookie = await getSessionCookie(page);
+
+    // Create a comparison to ensure we have data
+    const res = await page.request.post(resolveUrl("/api/compare"), {
+      data: { query: "Cats vs Dogs", items: ["Cats", "Dogs"] },
+      headers: { "Content-Type": "application/json", Cookie: cookie, Accept: "text/event-stream" },
+      timeout: 120_000,
+    });
+
+    if (res.ok()) {
+      const body = Buffer.from((await res.body()) ?? []).toString("utf-8");
+      const events = await parseSSEStream(body);
+      const done = lastSSEOfType(events, "done") as Record<string, unknown> | undefined;
+      if (done) {
+        testSlug = (done.done as Record<string, unknown>).slug as string;
+      }
+    }
+  });
+
+  test("1. User comparisons list returns 200 for authenticated user", async ({ page }) => {
+    const res = await page.request.get(resolveUrl("/api/user/comparisons"), {
+      headers: { Cookie: cookie },
+    });
+    expect(res.status()).toBe(200);
+    const data = await res.json();
+    expect(Array.isArray(data)).toBe(true);
+  });
+
+  test("2. User comparisons list requires auth", async ({ page }) => {
+    const res = await page.request.get(resolveUrl("/api/user/comparisons"));
+    expect(res.status()).toBe(401);
+  });
+
+  test("3. Get comparison by slug returns 200 with data", async ({ page }) => {
+    if (!testSlug) { test.skip(); return; }
+
+    const res = await page.request.get(resolveUrl(`/api/comparisons/${testSlug}`), {
+      headers: { Cookie: cookie },
+    });
+    expect(res.status()).toBe(200);
+    const data = await res.json();
+    expect(data).toHaveProperty("slug", testSlug);
+    expect(data).toHaveProperty("status");
+    expect(["completed", "failed", "researching"]).toContain(data.status);
+  });
+
+  test("4. Get comparison by non-existent slug returns 404", async ({ page }) => {
+    const res = await page.request.get(resolveUrl("/api/comparisons/this-slug-does-not-exist-xyz123"), {
+      headers: { Cookie: cookie },
+    });
+    expect(res.status()).toBe(404);
+  });
+
+  test("5. Comparison slug increments view count", async ({ page }) => {
+    if (!testSlug) { test.skip(); return; }
+
+    const res1 = await page.request.get(resolveUrl(`/api/comparisons/${testSlug}`), {
+      headers: { Cookie: cookie },
+    });
+    const viewsBefore = (await res1.json()).viewCount ?? 0;
+
+    const res2 = await page.request.get(resolveUrl(`/api/comparisons/${testSlug}`), {
+      headers: { Cookie: cookie },
+    });
+    const viewsAfter = (await res2.json()).viewCount ?? 0;
+
+    expect(viewsAfter).toBeGreaterThanOrEqual(viewsBefore);
+  });
+
+  test("6. Comparison response includes all required fields", async ({ page }) => {
+    if (!testSlug) { test.skip(); return; }
+
+    const res = await page.request.get(resolveUrl(`/api/comparisons/${testSlug}`), {
+      headers: { Cookie: cookie },
+    });
+    const data = await res.json();
+    expect(data).toHaveProperty("id");
+    expect(data).toHaveProperty("title");
+    expect(data).toHaveProperty("slug");
+    expect(data).toHaveProperty("status");
+    expect(data).toHaveProperty("query");
+  });
+});