fix(tbank): reset connection-derived query cache

src/entities/portfolio/api/usePortfolio.test.tsx

@@ -1,10 +1,12 @@
 import { MantineProvider } from "@mantine/core";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 import { renderHook, waitFor } from "@testing-library/react";
+import { HttpResponse, http } from "msw";
 import type { FC, PropsWithChildren } from "react";
 import { afterEach, describe, expect, it, vi } from "vitest";
 
 import { configureAuthClient } from "@/shared/api";
+import { server } from "@/test/server";
 import { usePortfolio } from "./usePortfolio";
 
 describe("usePortfolio", () => {
@@ -34,4 +36,45 @@ describe("usePortfolio", () => {
 		await waitFor(() => expect(result.current.isSuccess).toBe(true));
 		expect(result.current.data).toMatchObject({ positions: [] });
 	});
+
+	it("keeps the current connection snapshot after a background refetch error", async () => {
+		configureAuthClient({
+			accessToken: () => "token",
+			refresh: async () => true,
+			clear: vi.fn(),
+		});
+		let calls = 0;
+		server.use(
+			http.get("*/api/v1/brokerage-accounts/:accountId/portfolio", () => {
+				calls += 1;
+				return calls === 1
+					? HttpResponse.json({
+							lastSuccessfulAt: "2026-08-14T00:00:00Z",
+							isStale: false,
+							totalsByCurrency: [],
+							positions: [],
+							cashBalances: [],
+						})
+					: HttpResponse.json({ code: "TBANK_UNAVAILABLE" }, { status: 503 });
+			}),
+		);
+		const client = new QueryClient();
+		const wrapper: FC<PropsWithChildren> = (props) => {
+			const { children } = props;
+			return (
+				<MantineProvider>
+					<QueryClientProvider client={client}>{children}</QueryClientProvider>
+				</MantineProvider>
+			);
+		};
+		const { result } = renderHook(() => usePortfolio("account-1"), { wrapper });
+
+		await waitFor(() => expect(result.current.isSuccess).toBe(true));
+		void result.current.refetch();
+		await waitFor(() => expect(result.current.isError).toBe(true));
+
+		expect(result.current.data).toMatchObject({
+			lastSuccessfulAt: "2026-08-14T00:00:00Z",
+		});
+	});
 });