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/lib/state/offers_cubit.dart

@@ -10,6 +10,7 @@ import '../services/offer_mapper.dart';
 import '../services/offer_outbox.dart';
 import '../services/offer_thumbnail.dart';
 import '../services/social_connection.dart';
+import '../services/social_service.dart';
 
 /// State of the offer discovery/publish screen. Transport-agnostic — it holds
 /// only what the UI shows, never a relay handle.
@@ -28,6 +29,7 @@ class OffersState extends Equatable {
     this.nextPageCursor,
     this.publishing = false,
     this.hasSearched = false,
+    this.connectionEpoch = 0,
     this.error,
   });
 
@@ -80,6 +82,11 @@ class OffersState extends Equatable {
   /// from "searched, found nothing".
   final bool hasSearched;
 
+  /// Bumped whenever the underlying transport comes or goes, so the UI rebuilds
+  /// and re-reads [OffersCubit.isOnline] — states differing only here are
+  /// otherwise Equatable-equal and bloc would skip the emit.
+  final int connectionEpoch;
+
   /// Last error, in human terms for the UI (null when fine).
   final String? error;
 
@@ -136,6 +143,7 @@ class OffersState extends Equatable {
     int? Function()? nextPageCursor,
     bool? publishing,
     bool? hasSearched,
+    int? connectionEpoch,
     String? Function()? error,
   }) {
     return OffersState(
@@ -153,6 +161,7 @@ class OffersState extends Equatable {
           nextPageCursor != null ? nextPageCursor() : this.nextPageCursor,
       publishing: publishing ?? this.publishing,
       hasSearched: hasSearched ?? this.hasSearched,
+      connectionEpoch: connectionEpoch ?? this.connectionEpoch,
       error: error != null ? error() : this.error,
     );
   }
@@ -172,6 +181,7 @@ class OffersState extends Equatable {
         nextPageCursor,
         publishing,
         hasSearched,
+        connectionEpoch,
         error,
       ];
 }
@@ -183,15 +193,40 @@ class OffersState extends Equatable {
 class OffersCubit extends Cubit<OffersState> {
   OffersCubit(
     this._transport, {
+    SocialConnection? connection,
     Future<Uint8List?> Function(String varietyId)? coverPhoto,
     String? Function(Uint8List bytes)? thumbnail,
     Future<void> Function()? onDispose,
   })  : _coverPhoto = coverPhoto,
         _thumbnail = thumbnail,
         _onDispose = onDispose,
-        super(const OffersState());
+        super(const OffersState()) {
+    // Fresh-install fix: the transport captured at build time may be null while
+    // the shared connection is still coming up (or dropped). Follow the
+    // connection so the market recovers by itself instead of staying offline
+    // until a manual retry.
+    _connSub = connection?.sessions.listen(_onSession);
+  }
 
-  final OfferTransport? _transport;
+  OfferTransport? _transport;
+  StreamSubscription<SocialSession?>? _connSub;
+
+  /// The last area prefix asked of [discover]; re-run when the connection
+  /// (re)appears so results show without the user tapping anything.
+  String? _lastPrefix;
+
+  void _onSession(SocialSession? session) {
+    if (isClosed) return;
+    final transport = session?.offers;
+    if (identical(transport, _transport)) return;
+    _transport = transport;
+    final prefix = _lastPrefix;
+    if (transport != null && prefix != null) {
+      unawaited(discover(prefix)); // emits fresh states as results arrive
+    } else {
+      emit(state.copyWith(connectionEpoch: state.connectionEpoch + 1));
+    }
+  }
 
   /// Fetches a variety's cover photo bytes; null in tests or when no inventory
   /// repo is wired.
@@ -225,6 +260,7 @@ class OffersCubit extends Cubit<OffersState> {
   /// from now on — older results arrive via [loadNextPage], not by draining the
   /// whole area into memory.
   Future<void> discover(String geohashPrefix) async {
+    _lastPrefix = geohashPrefix;
     final transport = _transport;
     if (transport == null) {
       emit(state.copyWith(error: () => 'offline', hasSearched: true));
@@ -467,6 +503,7 @@ class OffersCubit extends Cubit<OffersState> {
   @override
   Future<void> close() async {
     _searchTimeout?.cancel();
+    await _connSub?.cancel();
     await _sub?.cancel();
     await _onDispose?.call();
     return super.close();
@@ -484,6 +521,7 @@ Future<OffersCubit> createOffersCubit(
   final session = await connection.session();
   return OffersCubit(
     session?.offers,
+    connection: connection, // keeps following (re)connects — see _onSession
     coverPhoto: repository?.coverPhotoFor,
     thumbnail: offerThumbnailDataUri,
   );