fix(cache): stop serving stale site-settings defaults after deploy

The site-settings loader kept an in-process map forever after a Redis miss
and promoted DEFAULTS (no logo/theme) to Redis on any DB error, so a build
that started before the DB was reachable stuck the site on the preset logo
and default theme until a manual reload or full restart.

- Redis miss now reloads from the database instead of the stale in-process map
- a DB failure returns defaults only as an in-process last resort and never
  writes them to Redis, so the shared cache can't be poisoned by a transient
  error at startup
- regression tests: DB re-read on Redis miss after cache expiry, defaults never
  promoted to Redis, recovery from transient DB failure

src/lib/services/site-settings.test.ts

@@ -1,6 +1,14 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
 
-const { selectFrom } = vi.hoisted(() => ({ selectFrom: vi.fn() }));
+const { selectFrom, redisMock } = vi.hoisted(() => ({
+	selectFrom: vi.fn(),
+	redisMock: {
+		get: vi.fn(),
+		setex: vi.fn(),
+		del: vi.fn(),
+	},
+}));
+
 vi.mock("@/lib/db", () => ({
 	db: {
 		select: () => ({
@@ -15,10 +23,18 @@ vi.mock("@/lib/db", () => ({
 	WebsiteSetting: { key: "WebsiteSetting.key", value: "WebsiteSetting.value" },
 }));
 
+vi.mock("@/lib/redis", () => ({ redis: redisMock }));
+
 import { siteSettings } from "./site-settings";
 
 beforeEach(async () => {
 	selectFrom.mockReset();
+	redisMock.get.mockReset();
+	redisMock.setex.mockReset();
+	redisMock.del.mockReset();
+	redisMock.get.mockResolvedValue(null);
+	redisMock.setex.mockResolvedValue(undefined);
+	redisMock.del.mockResolvedValue(undefined);
 	await siteSettings.reload();
 });
 
@@ -53,4 +69,33 @@ describe("siteSettings", () => {
 		await siteSettings.get("hotel_name");
 		expect(selectFrom).toHaveBeenCalledTimes(2);
 	});
+
+	it("re-reads the database on a Redis miss instead of serving stale cache", async () => {
+		vi.useFakeTimers();
+		try {
+			selectFrom.mockResolvedValue([{ key: "hotel_name", value: "First" }]);
+			expect(await siteSettings.get("hotel_name")).toBe("First");
+
+			selectFrom.mockResolvedValue([{ key: "hotel_name", value: "Second" }]);
+			vi.setSystemTime(Date.now() + 2 * 60_000); // expire the in-memory cache
+			expect(await siteSettings.get("hotel_name")).toBe("Second");
+		} finally {
+			vi.useRealTimers();
+		}
+	});
+
+	it("does not promote defaults to Redis when the database fails", async () => {
+		selectFrom.mockRejectedValue(new Error("db down"));
+		expect(await siteSettings.get("hotel_name", "fallback")).toBe("fallback");
+		expect(redisMock.setex).not.toHaveBeenCalled();
+	});
+
+	it("recovers from a transient database failure on the next load", async () => {
+		selectFrom.mockRejectedValueOnce(new Error("db down"));
+		expect(await siteSettings.get("hotel_name", "fallback")).toBe("fallback");
+
+		selectFrom.mockResolvedValueOnce([{ key: "hotel_name", value: "Live" }]);
+		expect(await siteSettings.get("hotel_name")).toBe("Live");
+		expect(redisMock.setex).toHaveBeenCalledTimes(1);
+	});
 });