Fix SetupGuard error handling and add retry UI

frontend/src/components/SetupGuard.tsx

@@ -7,7 +7,14 @@
  */
 
 import { Navigate } from "react-router-dom";
-import { Spinner, makeStyles } from "@fluentui/react-components";
+import {
+  Button,
+  MessageBar,
+  MessageBarBody,
+  Spinner,
+  makeStyles,
+  tokens,
+} from "@fluentui/react-components";
 import { useSetup } from "../hooks/useSetup";
 
 /**
@@ -22,7 +29,7 @@ interface SetupGuardProps {
 /**
  * Render `children` only when setup has been completed.
  *
- * Redirects to `/setup` if setup is still pending.
+ * Redirects to `/setup` only when setup status is known and incomplete.
  */
 const useStyles = makeStyles({
   loadingWrapper: {
@@ -31,11 +38,30 @@ const useStyles = makeStyles({
     alignItems: "center",
     minHeight: "100vh",
   },
+  errorContainer: {
+    display: "flex",
+    justifyContent: "center",
+    alignItems: "center",
+    minHeight: "100vh",
+    padding: tokens.spacingHorizontalM,
+    backgroundColor: tokens.colorNeutralBackground2,
+  },
+  errorCard: {
+    width: "100%",
+    maxWidth: "520px",
+    display: "flex",
+    flexDirection: "column",
+    gap: tokens.spacingVerticalM,
+    padding: tokens.spacingVerticalL,
+    backgroundColor: tokens.colorNeutralBackground1,
+    borderRadius: tokens.borderRadiusXLarge,
+    boxShadow: tokens.shadow8,
+  },
 });
 
 export function SetupGuard({ children }: SetupGuardProps): React.JSX.Element {
   const styles = useStyles();
-  const { status, loading } = useSetup();
+  const { status, loading, error, refresh } = useSetup();
 
   if (loading) {
     return (
@@ -45,6 +71,21 @@ export function SetupGuard({ children }: SetupGuardProps): React.JSX.Element {
     );
   }
 
+  if (error && status === null) {
+    return (
+      <div className={styles.errorContainer}>
+        <div className={styles.errorCard}>
+          <MessageBar intent="error">
+            <MessageBarBody>{error}</MessageBarBody>
+          </MessageBar>
+          <Button appearance="primary" onClick={() => void refresh()}>
+            Retry
+          </Button>
+        </div>
+      </div>
+    );
+  }
+
   if (!status?.completed) {
     return <Navigate to="/setup" replace />;
   }

frontend/src/components/__tests__/SetupGuard.test.tsx

@@ -1,5 +1,5 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
-import { render, screen, waitFor } from "@testing-library/react";
+import { fireEvent, render, screen, waitFor } from "@testing-library/react";
 import { MemoryRouter, Routes, Route } from "react-router-dom";
 import { FluentProvider, webLightTheme } from "@fluentui/react-components";
 import { SetupGuard } from "../SetupGuard";
@@ -65,13 +65,32 @@ describe("SetupGuard", () => {
     expect(screen.queryByTestId("protected-content")).not.toBeInTheDocument();
   });
 
-  it("redirects to /setup when the API call fails", async () => {
-    // Task 0.3: a failed check must redirect to /setup, not allow through.
+  it("renders an error card when the setup status check fails", async () => {
     mockedGetSetupStatus.mockRejectedValue(new Error("Network error"));
     renderGuard();
+
     await waitFor(() => {
-      expect(screen.getByTestId("setup-page")).toBeInTheDocument();
+      expect(screen.getByRole("button", { name: /retry/i })).toBeInTheDocument();
     });
+    expect(screen.getByText(/network error/i)).toBeInTheDocument();
     expect(screen.queryByTestId("protected-content")).not.toBeInTheDocument();
+    expect(screen.queryByTestId("setup-page")).not.toBeInTheDocument();
+  });
+
+  it("retries setup status fetch when Retry is clicked", async () => {
+    mockedGetSetupStatus.mockRejectedValueOnce(new Error("Network error"));
+    mockedGetSetupStatus.mockResolvedValueOnce({ completed: true });
+
+    renderGuard();
+
+    await waitFor(() => {
+      expect(screen.getByRole("button", { name: /retry/i })).toBeInTheDocument();
+    });
+
+    fireEvent.click(screen.getByRole("button", { name: /retry/i }));
+
+    await waitFor(() => {
+      expect(screen.getByTestId("protected-content")).toBeInTheDocument();
+    });
   });
 });