fix(shell): auth-rejected hub no longer reported as unreachable

The sustained-failure banner treated every failed health poll as
'can't reach the hub'. With token auth active, a wrong or rotated
token gets UNAUTHENTICATED from a perfectly reachable hub — the
old wording sent the operator to fix the endpoint. The shell now
uses the SDK's probe() and, on auth rejection, switches the banner
to 'rejected the sign-in — check the access token' (key-off icon,
DE+EN). Two widget tests pin the wording per failure kind and the
banner clearing once the probe turns serving.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

test/hub_banner_test.dart

@@ -0,0 +1,63 @@
+// The shell's sustained-failure banner must name the actual
+// problem: a hub that rejects the token (UNAUTHENTICATED /
+// PERMISSION_DENIED) is UP — telling the operator "can't reach
+// the hub" sends them to fix the endpoint when the token is what
+// needs attention. The probe result is faked through
+// StudioShellState.debugProbeOverride; the banner appears after
+// three consecutive failed polls (5 s apart), so each test pumps
+// the poll timer forward instead of waiting.
+
+import 'package:chain_client_sdk/chain_client_sdk.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:chain_studio/data/hub.dart';
+import 'package:chain_studio/main.dart';
+
+Future<void> _pumpShell(WidgetTester tester) async {
+  await tester.pumpWidget(
+    const StudioApp(
+      initialThemeMode: ThemeModeValue.system,
+      initialLocale: Locale('en'),
+    ),
+  );
+  // pump (not pumpAndSettle): the app has long-lived timers that
+  // never settle. One frame lays the shell out, then three poll
+  // ticks cross the banner threshold.
+  await tester.pump(const Duration(milliseconds: 100));
+  for (var i = 0; i < 3; i++) {
+    await tester.pump(const Duration(seconds: 5));
+    await tester.pump();
+  }
+}
+
+void main() {
+  tearDown(() {
+    StudioShellState.debugProbeOverride = null;
+  });
+
+  testWidgets('sustained auth rejection points at the token, not the wire',
+      (tester) async {
+    StudioShellState.debugProbeOverride =
+        () async => HubProbeResult.authRejected;
+    await _pumpShell(tester);
+
+    expect(find.textContaining('rejected the sign-in'), findsOneWidget);
+    expect(find.textContaining("Can't reach"), findsNothing);
+
+    // Token fixed (probe turns serving): the banner must clear.
+    StudioShellState.debugProbeOverride = () async => HubProbeResult.serving;
+    await tester.pump(const Duration(seconds: 5));
+    await tester.pump();
+    expect(find.textContaining('rejected the sign-in'), findsNothing);
+  });
+
+  testWidgets('sustained connection failure keeps the unreachable wording',
+      (tester) async {
+    StudioShellState.debugProbeOverride =
+        () async => HubProbeResult.unreachable;
+    await _pumpShell(tester);
+
+    expect(find.textContaining("Can't reach"), findsOneWidget);
+    expect(find.textContaining('rejected the sign-in'), findsNothing);
+  });
+}