feat(api): add DB-touching /api/readyz so schema loss cannot hide behind /health (GRO-2678)

- Register GET /api/readyz after /api/health in src/index.ts (before authMiddleware)
- Runs `getDb().select({id: staff.id}).from(staff).limit(1)` inside try/catch
- Success → 200 {"status":"ready"}; failure → 503 {"status":"degraded","check":"db"}
- Raw driver error is console.error'd but never leaked to the response body
- /health and /api/health are unchanged (K8s probes remain DB-less per CTO decision)
- New unit tests: mock getDb to resolve → assert 200/ready; throw → assert 503/degraded
- Updated UAT_PLAYBOOK.md §4.0 with TC-API-0.2 and TC-API-0.3

Co-Authored-By: Paperclip <noreply@paperclip.ing>

UAT_PLAYBOOK.md

@@ -65,8 +65,11 @@ Expected: one row, `role = 'groomer'`. If zero rows return, the request hit the
 | # | Scenario | Steps | Expected |
 |---|----------|-------|----------|
 | TC-API-0.1 | Unauthenticated health check | GET /api/health | 200 OK, `{"status":"ok"}` |
+| TC-API-0.2 | DB-touching readiness check — healthy (GRO-2678) | GET /api/readyz | 200 OK, `{"status":"ready"}` |
+| TC-API-0.3 | DB-touching readiness check — response body safe | GET /api/readyz and inspect body | Body contains only `status` and (on error) `check` fields — no raw SQL, driver messages, or stack traces |
 
 > **Note (GRO-1544):** Health endpoint registered on `api` basePath before auth middleware at `/api/health`. The old path `/health` was incorrect (routed to web pod via HTTPRoute `/*` rule).
+> **Note (GRO-2678):** `/api/readyz` is a separate DB-touching endpoint for monitoring. It is intentionally NOT used for K8s liveness/readiness probes — those remain DB-less to avoid pod cycling on transient DB blips.
 
 ### 4.1 Authentication
 

src/__tests__/readyz.test.ts

@@ -0,0 +1,87 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { Hono } from "hono";
+
+// ─── Mock db module ───────────────────────────────────────────────────────────
+
+let selectImpl: () => Promise<unknown>;
+
+vi.mock("@groombook/db", () => {
+  const staff = new Proxy(
+    { _name: "staff" },
+    {
+      get(_target, prop) {
+        if (prop === "_name") return "staff";
+        return { table: "staff", column: prop };
+      },
+    }
+  );
+
+  return {
+    getDb: () => ({
+      select: (_fields: unknown) => ({
+        from: (_table: unknown) => ({
+          limit: (_n: number) => selectImpl(),
+        }),
+      }),
+    }),
+    staff,
+  };
+});
+
+// ─── Build test app ───────────────────────────────────────────────────────────
+
+async function makeApp() {
+  // Import after mocks are in place
+  const { getDb, staff } = await import("@groombook/db");
+
+  const app = new Hono();
+  app.get("/api/readyz", async (c) => {
+    try {
+      await getDb().select({ id: staff.id }).from(staff).limit(1);
+      return c.json({ status: "ready" }, 200);
+    } catch (err) {
+      console.error("[readyz] DB check failed:", err);
+      return c.json({ status: "degraded", check: "db" }, 503);
+    }
+  });
+  return app;
+}
+
+// ─── Tests ────────────────────────────────────────────────────────────────────
+
+describe("GET /api/readyz", () => {
+  beforeEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("returns 200 {status:'ready'} when DB query succeeds", async () => {
+    selectImpl = () => Promise.resolve([{ id: "staff-1" }]);
+
+    const app = await makeApp();
+    const res = await app.request("/api/readyz", { method: "GET" });
+    const body = (await res.json()) as Record<string, unknown>;
+
+    expect(res.status).toBe(200);
+    expect(body.status).toBe("ready");
+  });
+
+  it("returns 503 {status:'degraded',check:'db'} when DB query throws", async () => {
+    selectImpl = () => Promise.reject(new Error("42P01: relation staff does not exist"));
+
+    const consoleSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+
+    const app = await makeApp();
+    const res = await app.request("/api/readyz", { method: "GET" });
+    const body = (await res.json()) as Record<string, unknown>;
+
+    expect(res.status).toBe(503);
+    expect(body.status).toBe("degraded");
+    expect(body.check).toBe("db");
+
+    // Raw SQL / driver error must NOT appear in the response body
+    expect(JSON.stringify(body)).not.toContain("42P01");
+    expect(JSON.stringify(body)).not.toContain("relation");
+
+    consoleSpy.mockRestore();
+  });
+});

src/index.ts

@@ -65,6 +65,17 @@ app.use(
 app.get("/health", (c) => c.json({ status: "ok" }));
 // /api/health: used by Gateway HTTPRoute (/api/* → API pod)
 app.get("/api/health", (c) => c.json({ status: "ok" }));
+// /api/readyz: DB-touching deep health check consumed by monitoring (not K8s probes)
+// Distinct from /health so a dropped schema triggers an alert without cycling pods (GRO-2678)
+app.get("/api/readyz", async (c) => {
+  try {
+    await getDb().select({ id: staff.id }).from(staff).limit(1);
+    return c.json({ status: "ready" }, 200);
+  } catch (err) {
+    console.error("[readyz] DB check failed:", err);
+    return c.json({ status: "degraded", check: "db" }, 503);
+  }
+});
 
 // Public booking routes — no auth required, must be registered before auth middleware
 app.route("/api/book", bookRouter);