Web vitals: prefer external RUM

tests/unit/webVitalsMode.test.ts

@@ -0,0 +1,36 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { getWebVitalsStorageMode } from "../../lib/server/webVitals/mode";
+
+describe("getWebVitalsStorageMode", () => {
+  afterEach(() => {
+    vi.unstubAllEnvs();
+  });
+
+  it("returns external when WEB_VITALS_STORAGE=external", () => {
+    vi.stubEnv("WEB_VITALS_STORAGE", "external");
+    vi.stubEnv("NODE_ENV", "development");
+    expect(getWebVitalsStorageMode()).toBe("external");
+  });
+
+  it("returns local when WEB_VITALS_STORAGE=local", () => {
+    vi.stubEnv("WEB_VITALS_STORAGE", "local");
+    vi.stubEnv("NODE_ENV", "production");
+    expect(getWebVitalsStorageMode()).toBe("local");
+  });
+
+  it("defaults to external in production when unset", () => {
+    vi.stubEnv("NODE_ENV", "production");
+    expect(getWebVitalsStorageMode()).toBe("external");
+  });
+
+  it("defaults to local in development when unset", () => {
+    vi.stubEnv("NODE_ENV", "development");
+    expect(getWebVitalsStorageMode()).toBe("local");
+  });
+
+  it("maps database to external until implemented", () => {
+    vi.stubEnv("WEB_VITALS_STORAGE", "database");
+    vi.stubEnv("NODE_ENV", "development");
+    expect(getWebVitalsStorageMode()).toBe("external");
+  });
+});