refactor(fe): share the SaaS PAYG experience with desktop via a cloud/ layer (#6649)

Co-authored-by: James Brunton <[email protected]>

frontend/editor/src/desktop/services/httpErrorHandler.test.ts

@@ -0,0 +1,51 @@
+import { describe, expect, test, vi, beforeEach, afterEach } from "vitest";
+import { OPEN_SIGN_IN_EVENT } from "@app/constants/signInEvents";
+import { FREE_LIMIT_MODAL_EVENT } from "@app/components/usageLimitModals";
+import { handleHttpError } from "@app/services/httpErrorHandler";
+
+// The non-PAYG path delegates to core; stub it so these cases stay isolated.
+vi.mock("@core/services/httpErrorHandler", () => ({
+  handleHttpError: vi.fn().mockResolvedValue(false),
+}));
+
+function axiosErr(
+  status: number,
+  sentinel: string,
+  extra: Record<string, unknown> = {},
+) {
+  return {
+    isAxiosError: true,
+    response: { status, data: { error: sentinel, ...extra } },
+  };
+}
+
+describe("desktop handleHttpError — PAYG sentinels", () => {
+  let events: string[];
+  let listener: (e: Event) => void;
+
+  beforeEach(() => {
+    events = [];
+    listener = (e: Event) => events.push(e.type);
+    window.addEventListener(OPEN_SIGN_IN_EVENT, listener);
+    window.addEventListener(FREE_LIMIT_MODAL_EVENT, listener);
+  });
+  afterEach(() => {
+    window.removeEventListener(OPEN_SIGN_IN_EVENT, listener);
+    window.removeEventListener(FREE_LIMIT_MODAL_EVENT, listener);
+  });
+
+  test("401 SIGNUP_REQUIRED opens the desktop sign-in modal", async () => {
+    const handled = await handleHttpError(axiosErr(401, "SIGNUP_REQUIRED"));
+    expect(handled).toBe(true);
+    expect(events).toContain(OPEN_SIGN_IN_EVENT);
+  });
+
+  test("402 FEATURE_DEGRADED (free) pops the limit modal, not sign-in", async () => {
+    const handled = await handleHttpError(
+      axiosErr(402, "FEATURE_DEGRADED", { subscribed: false }),
+    );
+    expect(handled).toBe(true);
+    expect(events).toContain(FREE_LIMIT_MODAL_EVENT);
+    expect(events).not.toContain(OPEN_SIGN_IN_EVENT);
+  });
+});