fix(market): recover by itself when the shared connection comes up

Fresh installs could sit on 'can't reach the servers' forever: the offers
cubit captured the transport once at build time, the shared connection only
retried on a connectivity CHANGE, and a silently-filtered relay could stall
the pool for minutes.

- SocialConnection: retry with backoff after a failed attempt while started
  and not knowingly offline (injectable schedule for tests)
- OffersCubit: follow connection.sessions, re-attach the transport and re-run
  the last discovery on (re)connect; announce drops via connectionEpoch
- market _init: record the wanted area on the cubit even while offline
- NostrOfferTransport.discoverPage: sort a copy (channel lists may be
  unmodifiable)

apps/app_seeds/test/state/offers_cubit_test.dart

@@ -7,7 +7,11 @@ import 'package:tane/data/variety_repository.dart';
 import 'package:tane/db/enums.dart';
 import 'package:tane/services/discovery_area.dart';
 import 'package:tane/services/offer_mapper.dart';
+import 'package:nostr/nostr.dart';
 import 'package:tane/services/offer_outbox.dart';
+import 'package:tane/services/social_connection.dart';
+import 'package:tane/services/social_service.dart';
+import 'package:tane/services/social_settings.dart';
 import 'package:tane/state/offers_cubit.dart';
 
 import '../support/test_support.dart';
@@ -835,4 +839,111 @@ void main() {
       await cubit.close();
     });
   });
+
+  group('connection recovery (fresh-install fix)', () {
+    const seedHex =
+        '000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f';
+
+    late SocialService social;
+    late SocialSettings settings;
+
+    setUp(() async {
+      social = await SocialService.fromRootSeedHex(seedHex);
+      settings = SocialSettings(InMemorySecretStore());
+    });
+
+    SocialConnection makeConnection({
+      required bool Function() down,
+      Stream<bool>? online,
+    }) =>
+        SocialConnection(
+          social: social,
+          settings: settings,
+          online: online ?? const Stream.empty(),
+          retrySchedule: const [Duration(milliseconds: 5)],
+          open: (_) async {
+            if (down()) throw StateError('unreachable');
+            return SocialSession(_NoopChannel());
+          },
+        );
+
+    test('comes online by itself when the shared connection connects later',
+        () async {
+      var down = true;
+      final conn = makeConnection(down: () => down);
+      final cubit = await createOffersCubit(conn);
+      expect(cubit.isOnline, isFalse); // built while unreachable
+
+      final epochBefore = cubit.state.connectionEpoch;
+      conn.start();
+      down = false; // network path recovers; backoff retry reconnects
+      await Future<void>.delayed(const Duration(milliseconds: 100));
+
+      expect(cubit.isOnline, isTrue, reason: 'no manual Retry needed');
+      expect(cubit.state.connectionEpoch, greaterThan(epochBefore),
+          reason: 'a state was emitted so the UI re-reads isOnline');
+
+      await cubit.close();
+      await conn.dispose();
+    });
+
+    test('re-runs the last discovery when the connection recovers', () async {
+      var down = true;
+      final conn = makeConnection(down: () => down);
+      final cubit = await createOffersCubit(conn);
+
+      await cubit.discover('sp3e9'); // offline → error, but the wish is kept
+      expect(cubit.state.error, 'offline');
+
+      conn.start();
+      down = false;
+      await Future<void>.delayed(const Duration(milliseconds: 100));
+
+      expect(cubit.isOnline, isTrue);
+      expect(cubit.state.areaGeohash, 'sp3e9', reason: 'discovery re-ran');
+      expect(cubit.state.hasSearched, isTrue);
+      expect(cubit.state.error, isNull, reason: 'offline error cleared');
+
+      await cubit.close();
+      await conn.dispose();
+    });
+
+    test('goes offline (and tells the UI) when the session drops', () async {
+      final online = StreamController<bool>.broadcast();
+      final conn = makeConnection(down: () => false, online: online.stream);
+      conn.start();
+      await pumpEventQueue();
+      final cubit = await createOffersCubit(conn);
+      expect(cubit.isOnline, isTrue);
+
+      final epochBefore = cubit.state.connectionEpoch;
+      online.add(false); // network lost
+      await pumpEventQueue();
+
+      expect(cubit.isOnline, isFalse);
+      expect(cubit.state.connectionEpoch, greaterThan(epochBefore));
+
+      await cubit.close();
+      await conn.dispose();
+      await online.close();
+    });
+  });
+}
+
+/// A no-op [NostrChannel]: just enough to build a [SocialSession] whose offer
+/// transport answers with empty results.
+class _NoopChannel implements NostrChannel {
+  @override
+  String get privateKeyHex => '00' * 32;
+  @override
+  String get publicKeyHex => 'ab' * 32;
+  @override
+  Future<({bool accepted, String message})> publish(Event event) async =>
+      (accepted: true, message: '');
+  @override
+  Stream<Event> subscribe(Filter filter) => const Stream.empty();
+  @override
+  Future<List<Event>> reqOnce(Filter filter) async => const [];
+  @override
+  Future<void> close() async {}
 }