feat(block2): Nostr transport backend in commons_core (all 3 contracts)

Second production slice: the concrete Nostr backend on the shared connection,
using the vetted nostr package's crypto (NIP-44 spec-vector tested, gift wrap).

- NostrConnection: one dart:io WebSocket + identity + EVENT/OK, REQ/EOSE via
  the library's Event/Filter/Request. Pure Dart, no Flutter.
- NostrOfferTransport (NIP-99 kind 30402) + Nip99Codec: geohash coarsened to a
  NIP-52 prefix ladder on the wire; Offer stays inventory/location-agnostic.
- NostrMessageTransport (NIP-17): send/inbox via the library's DirectMessage
  gift-wrap onion.
- NostrTrustTransport (custom addressable kind 30777): certify/revoke/discover.
- MiniRelay test support + integration tests: offers, messaging (metadata
  privacy), WoT membership + revoke, and trust-filters-offers — all over ONE
  shared connection, hermetic in-process relay.

Renamed the core offer lifecycle enum OfferStatus -> OfferLifecycle to avoid
colliding with app_seeds' sharing-intent OfferStatus (no Block 1 code touched;
app_seeds analyzes clean, 0 errors). commons_core: 55 tests green.

packages/commons_core/lib/commons_core.dart

@@ -13,6 +13,10 @@ export 'src/identity/nostr_key_derivation.dart';
 export 'src/ids/id_gen.dart';
 export 'src/social/certification.dart';
 export 'src/social/message_transport.dart';
+export 'src/social/nostr/nostr_connection.dart';
+export 'src/social/nostr/nostr_message_transport.dart';
+export 'src/social/nostr/nostr_offer_transport.dart';
+export 'src/social/nostr/nostr_trust_transport.dart';
 export 'src/social/offer.dart';
 export 'src/social/offer_transport.dart';
 export 'src/social/trust_transport.dart';

packages/commons_core/lib/src/social/nostr/nip99_codec.dart

@@ -0,0 +1,97 @@
+import 'package:nostr/nostr.dart';
+
+import '../offer.dart';
+
+/// Maps [Offer] ↔ Nostr NIP-99 "Classified Listing" events (kind 30402).
+///
+/// This codec enforces the privacy contract on the wire: the only location that
+/// ever leaves the device is a coarse geohash, truncated here to
+/// [maxGeohashChars] and emitted as a NIP-52 prefix ladder so area queries match
+/// by exact tag. [Offer] itself has no field that could carry inventory or an
+/// exact address — the seam does the work.
+class Nip99Codec {
+  /// NIP-99 addressable classified listing.
+  static const kindActive = 30402;
+
+  /// A 5-char geohash ≈ ±2.4 km cell — the coarse "near you" of the mocks.
+  static const maxGeohashChars = 5;
+
+  /// Builds the signed tags + content for [offer]. Signing happens in the
+  /// transport via `Event.from`.
+  ({List<List<String>> tags, String content}) encode(Offer offer) {
+    final coarse = _coarsen(offer.approxGeohash);
+    final tags = <List<String>>[
+      ['d', offer.id],
+      ['title', offer.summary],
+      ['status', offer.status == OfferLifecycle.active ? 'active' : 'sold'],
+      ['offer_type', offer.type.name],
+    ];
+    for (var i = 1; i <= coarse.length; i++) {
+      tags.add(['g', coarse.substring(0, i)]); // NIP-52 prefix ladder, coarse only
+    }
+    if (offer.category != null) tags.add(['t', offer.category!]);
+    if (offer.radiusKm != null) tags.add(['radius_km', '${offer.radiusKm}']);
+    if (offer.type == OfferType.sale && offer.priceAmount != null) {
+      tags.add(['price', '${offer.priceAmount}', offer.priceCurrency ?? 'EUR']);
+    }
+    if (offer.type == OfferType.exchange && offer.exchangeTerms != null) {
+      tags.add(['exchange_terms', offer.exchangeTerms!]);
+    }
+    if (offer.imageUrl != null) tags.add(['image', offer.imageUrl!]);
+    if (offer.expiresAt != null) {
+      tags.add(['expiration', '${offer.expiresAt!.millisecondsSinceEpoch ~/ 1000}']);
+    }
+    return (tags: tags, content: offer.summary);
+  }
+
+  /// Reconstructs an [Offer] from a received event.
+  Offer decode(Event event) {
+    final price = _tag(event, 'price');
+    return Offer(
+      id: _tagValue(event, 'd') ?? event.id,
+      authorPubkeyHex: event.pubkey,
+      summary: _tagValue(event, 'title') ?? event.content,
+      type: _parseType(_tagValue(event, 'offer_type')),
+      status: _tagValue(event, 'status') == 'sold'
+          ? OfferLifecycle.closed
+          : OfferLifecycle.active,
+      category: _tagValue(event, 't'),
+      approxGeohash: _longestGeohash(event),
+      radiusKm: int.tryParse(_tagValue(event, 'radius_km') ?? ''),
+      priceAmount: price != null && price.length > 1 ? num.tryParse(price[1]) : null,
+      priceCurrency: price != null && price.length > 2 ? price[2] : null,
+      exchangeTerms: _tagValue(event, 'exchange_terms'),
+      imageUrl: _tagValue(event, 'image'),
+    );
+  }
+
+  String _coarsen(String g) =>
+      g.length > maxGeohashChars ? g.substring(0, maxGeohashChars) : g;
+
+  String _longestGeohash(Event e) {
+    var best = '';
+    for (final t in e.tags) {
+      if (t.isNotEmpty && t[0] == 'g' && t.length > 1 && t[1].length > best.length) {
+        best = t[1];
+      }
+    }
+    return best;
+  }
+
+  String? _tagValue(Event e, String name) {
+    for (final t in e.tags) {
+      if (t.isNotEmpty && t[0] == name && t.length > 1) return t[1];
+    }
+    return null;
+  }
+
+  List<String>? _tag(Event e, String name) {
+    for (final t in e.tags) {
+      if (t.isNotEmpty && t[0] == name) return t;
+    }
+    return null;
+  }
+
+  OfferType _parseType(String? name) =>
+      OfferType.values.firstWhere((t) => t.name == name, orElse: () => OfferType.gift);
+}

packages/commons_core/lib/src/social/nostr/nostr_connection.dart

@@ -0,0 +1,107 @@
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:nostr/nostr.dart';
+
+import '../../identity/nostr_key_derivation.dart';
+
+/// The ONE piece shared by every Nostr-backed transport: a single relay socket
+/// plus the signing identity and the EVENT/OK, REQ/EOSE lifecycle.
+/// [OfferTransport], [MessageTransport] and [TrustTransport] each sit on top of
+/// this — they share this *connection*, not a *contract*.
+///
+/// Pure Dart (`dart:io` WebSocket) — no Flutter. A production relay *pool*
+/// (multiple relays, reconnection, backoff) would wrap several of these; the
+/// spike/foundation uses one relay.
+class NostrConnection {
+  NostrConnection._(this._socket, this.identity) {
+    _socket.listen(_onData, onDone: _onDone, onError: (_) => _onDone());
+  }
+
+  final WebSocket _socket;
+
+  /// The derived identity this connection signs with.
+  final NostrIdentity identity;
+
+  String get publicKeyHex => identity.publicKeyHex;
+  String get privateKeyHex => identity.privateKeyHex;
+
+  final _incoming = StreamController<List<dynamic>>.broadcast();
+  int _subCounter = 0;
+
+  static Future<NostrConnection> connect(
+    String relayUrl, {
+    required NostrIdentity identity,
+  }) async {
+    final socket = await WebSocket.connect(relayUrl);
+    return NostrConnection._(socket, identity);
+  }
+
+  void _onData(dynamic d) {
+    if (!_incoming.isClosed) _incoming.add(jsonDecode(d as String) as List);
+  }
+
+  void _onDone() {
+    if (!_incoming.isClosed) _incoming.close();
+  }
+
+  /// Publishes an already-signed [event]; resolves with the relay's OK verdict.
+  Future<({bool accepted, String message})> publish(Event event) async {
+    final ok = _incoming.stream.firstWhere(
+      (m) => m[0] == 'OK' && m[1] == event.id,
+    );
+    _socket.add(jsonEncode(['EVENT', event.toMap()]));
+    final r = await ok.timeout(const Duration(seconds: 10));
+    return (accepted: r[2] as bool, message: r.length > 3 ? r[3] as String : '');
+  }
+
+  /// Streams events matching [filter] (live), until the caller cancels.
+  Stream<Event> subscribe(Filter filter) {
+    final subId = 'sub${_subCounter++}';
+    late StreamController<Event> controller;
+    StreamSubscription? sub;
+    controller = StreamController<Event>(
+      onListen: () {
+        sub = _incoming.stream.listen((m) {
+          if (m[0] == 'EVENT' && m[1] == subId) {
+            controller.add(
+              Event.fromMap(m[2] as Map<String, dynamic>, verify: false),
+            );
+          }
+        });
+        _socket.add(Request(subscriptionId: subId, filters: [filter]).serialize());
+      },
+      onCancel: () async {
+        _socket.add(jsonEncode(['CLOSE', subId]));
+        await sub?.cancel();
+      },
+    );
+    return controller.stream;
+  }
+
+  /// Collects stored events matching [filter] up to EOSE, then closes the sub.
+  Future<List<Event>> reqOnce(Filter filter) async {
+    final subId = 'once${_subCounter++}';
+    final results = <Event>[];
+    final done = Completer<void>();
+    final sub = _incoming.stream.listen((m) {
+      if (m[1] != subId) return;
+      if (m[0] == 'EVENT') {
+        results.add(Event.fromMap(m[2] as Map<String, dynamic>, verify: false));
+      } else if (m[0] == 'EOSE' && !done.isCompleted) {
+        done.complete();
+      }
+    });
+    _socket.add(Request(subscriptionId: subId, filters: [filter]).serialize());
+    await done.future.timeout(const Duration(seconds: 10));
+    _socket.add(jsonEncode(['CLOSE', subId]));
+    await sub.cancel();
+    return results;
+  }
+
+  Future<void> close() async {
+    await _socket.close();
+    if (!_incoming.isClosed) await _incoming.close();
+  }
+}

packages/commons_core/lib/src/social/nostr/nostr_message_transport.dart

@@ -0,0 +1,68 @@
+import 'dart:async';
+
+import 'package:nostr/nostr.dart' as nostr;
+
+import '../message_transport.dart';
+import 'nostr_connection.dart';
+
+/// NIP-17 private-DM backend for [MessageTransport], on the shared
+/// [NostrConnection]. The gift-wrap onion (rumor kind 14 → seal kind 13 → wrap
+/// kind 1059 signed by an ephemeral key) and the NIP-44 encryption are done by
+/// the vetted `nostr` package; we only route it over the relay.
+class NostrMessageTransport implements MessageTransport {
+  NostrMessageTransport(this._conn);
+
+  final NostrConnection _conn;
+
+  static const kindGiftWrap = 1059;
+
+  @override
+  Future<void> send({required String toPubkey, required String text}) async {
+    final wrap = await nostr.DirectMessage.create(
+      message: text,
+      authorSecretKey: _conn.privateKeyHex,
+      recipientPubkey: toPubkey,
+    );
+    final r = await _conn.publish(wrap);
+    if (!r.accepted) throw StateError('relay rejected gift wrap: ${r.message}');
+  }
+
+  @override
+  Stream<PrivateMessage> inbox() => _conn
+      .subscribe(nostr.Filter(kinds: const [kindGiftWrap], pTags: [_conn.publicKeyHex]))
+      .asyncMap(_unwrap)
+      .where((m) => m != null)
+      .cast<PrivateMessage>();
+
+  /// Collect the inbox up to EOSE (tests/one-shot).
+  Future<List<PrivateMessage>> inboxUntilEose() async {
+    final wraps = await _conn.reqOnce(
+      nostr.Filter(kinds: const [kindGiftWrap], pTags: [_conn.publicKeyHex]),
+    );
+    final out = <PrivateMessage>[];
+    for (final w in wraps) {
+      final m = await _unwrap(w);
+      if (m != null) out.add(m);
+    }
+    return out;
+  }
+
+  Future<PrivateMessage?> _unwrap(nostr.Event wrap) async {
+    try {
+      final rumor = await nostr.DirectMessage.parse(
+        giftWrap: wrap,
+        recipientSecretKey: _conn.privateKeyHex,
+      );
+      return PrivateMessage(
+        fromPubkey: rumor.pubkey,
+        text: rumor.content,
+        at: DateTime.fromMillisecondsSinceEpoch(rumor.createdAt * 1000),
+      );
+    } catch (_) {
+      return null; // not for us / wrong key / tampered
+    }
+  }
+
+  @override
+  Future<void> close() => _conn.close();
+}

packages/commons_core/lib/src/social/nostr/nostr_offer_transport.dart

@@ -0,0 +1,69 @@
+import 'package:nostr/nostr.dart';
+
+import '../offer.dart';
+import '../offer_transport.dart';
+import 'nip99_codec.dart';
+import 'nostr_connection.dart';
+
+/// Nostr NIP-99 backend for [OfferTransport], on a shared [NostrConnection].
+class NostrOfferTransport implements OfferTransport {
+  NostrOfferTransport(this._conn);
+
+  final NostrConnection _conn;
+  final Nip99Codec _codec = Nip99Codec();
+
+  Filter _filter(DiscoveryQuery q) => Filter(
+        kinds: const [Nip99Codec.kindActive],
+        tagFilters: {'g': [q.geohashPrefix]},
+        limit: q.limit,
+      );
+
+  @override
+  Future<PublishResult> publish(Offer offer) async {
+    final encoded = _codec.encode(offer);
+    final event = Event.from(
+      kind: Nip99Codec.kindActive,
+      content: encoded.content,
+      tags: encoded.tags,
+      secretKey: _conn.privateKeyHex,
+    );
+    final r = await _conn.publish(event);
+    return PublishResult(
+      accepted: r.accepted,
+      transportRef: event.id,
+      message: r.message,
+    );
+  }
+
+  @override
+  Stream<Offer> discover(DiscoveryQuery query) => _conn
+      .subscribe(_filter(query))
+      .map(_codec.decode)
+      .where((o) => query.types.isEmpty || query.types.contains(o.type));
+
+  /// Collects matches up to EOSE (tests/one-shot browse).
+  Future<List<Offer>> discoverUntilEose(DiscoveryQuery query) async {
+    final events = await _conn.reqOnce(_filter(query));
+    return events
+        .map(_codec.decode)
+        .where((o) => query.types.isEmpty || query.types.contains(o.type))
+        .toList();
+  }
+
+  @override
+  Future<void> retract(String offerId) async {
+    // NIP-09 deletion of the addressable coordinate; the OK path mirrors publish.
+    final event = Event.from(
+      kind: 5,
+      content: 'offer retracted',
+      tags: [
+        ['a', '${Nip99Codec.kindActive}:${_conn.publicKeyHex}:$offerId'],
+      ],
+      secretKey: _conn.privateKeyHex,
+    );
+    await _conn.publish(event);
+  }
+
+  @override
+  Future<void> close() => _conn.close();
+}

packages/commons_core/lib/src/social/nostr/nostr_trust_transport.dart

@@ -0,0 +1,97 @@
+import 'package:nostr/nostr.dart';
+
+import '../certification.dart';
+import '../trust_transport.dart';
+import 'nostr_connection.dart';
+
+/// Duniter-style certifications carried as Nostr events, on the shared
+/// [NostrConnection]. No settled NIP exists for a web of trust, so this uses a
+/// custom addressable kind mapped to the Duniter model (g1-integration.md "WoT
+/// propia pero compatible"): one live certification per (issuer, subject), so
+/// re-certifying renews and revoking replaces.
+class NostrTrustTransport implements TrustTransport {
+  NostrTrustTransport(this._conn);
+
+  final NostrConnection _conn;
+
+  /// Custom Tanemaki certification kind (addressable range).
+  static const kindCertification = 30777;
+
+  int get _now => DateTime.now().millisecondsSinceEpoch ~/ 1000;
+
+  @override
+  Future<void> certify({
+    required String subjectPubkey,
+    Duration validity = const Duration(days: 365),
+    String note = '',
+  }) =>
+      _publish(subjectPubkey, note: note, validity: validity, revoked: false);
+
+  @override
+  Future<void> revoke({required String subjectPubkey}) =>
+      _publish(subjectPubkey, note: '', validity: Duration.zero, revoked: true);
+
+  Future<void> _publish(
+    String subject, {
+    required String note,
+    required Duration validity,
+    required bool revoked,
+  }) async {
+    final event = Event.from(
+      kind: kindCertification,
+      content: note,
+      tags: [
+        ['p', subject],
+        ['d', subject],
+        ['status', revoked ? 'revoked' : 'valid'],
+        if (!revoked) ['expiration', '${_now + validity.inSeconds}'],
+      ],
+      secretKey: _conn.privateKeyHex,
+    );
+    final r = await _conn.publish(event);
+    if (!r.accepted) throw StateError('relay rejected cert: ${r.message}');
+  }
+
+  @override
+  Future<List<Certification>> allCertifications() async {
+    final events = await _conn.reqOnce(const Filter(kinds: [kindCertification]));
+    return events.map(_toCertification).toList();
+  }
+
+  @override
+  Future<Set<String>> certifiersOf(String subjectPubkey) async {
+    final events = await _conn.reqOnce(
+      Filter(kinds: const [kindCertification], pTags: [subjectPubkey]),
+    );
+    final now = DateTime.now();
+    return events
+        .map(_toCertification)
+        .where((c) => c.subject == subjectPubkey && c.isValidAt(now))
+        .map((c) => c.issuer)
+        .toSet();
+  }
+
+  Certification _toCertification(Event e) {
+    String? tag(String name) {
+      for (final t in e.tags) {
+        if (t.isNotEmpty && t[0] == name && t.length > 1) return t[1];
+      }
+      return null;
+    }
+
+    final exp = tag('expiration');
+    return Certification(
+      issuer: e.pubkey,
+      subject: tag('p') ?? tag('d') ?? '',
+      issuedAt: DateTime.fromMillisecondsSinceEpoch(e.createdAt * 1000),
+      expiresAt: exp == null
+          ? null
+          : DateTime.fromMillisecondsSinceEpoch(int.parse(exp) * 1000),
+      revoked: tag('status') == 'revoked',
+      note: e.content,
+    );
+  }
+
+  @override
+  Future<void> close() => _conn.close();
+}

packages/commons_core/lib/src/social/offer.dart

@@ -2,7 +2,10 @@
 /// reserves for a future "library of things".
 enum OfferType { gift, exchange, sale, wanted, lend }
 
-enum OfferStatus { active, reserved, closed }
+/// The published offer's lifecycle (distinct from the domain's local
+/// sharing-intent enum). Named `OfferLifecycle` to avoid colliding with
+/// app-side `OfferStatus`.
+enum OfferLifecycle { active, reserved, closed }
 
 /// A publishable offer — the "shop window", deliberately DECOUPLED from the
 /// domain's inventory (sharing-model.md §2, core-domain-boundary.md §4.3).
@@ -18,7 +21,7 @@ class Offer {
     required this.summary,
     required this.type,
     required this.approxGeohash,
-    this.status = OfferStatus.active,
+    this.status = OfferLifecycle.active,
     this.category,
     this.priceAmount,
     this.priceCurrency,
@@ -38,7 +41,7 @@ class Offer {
   final String summary;
 
   final OfferType type;
-  final OfferStatus status;
+  final OfferLifecycle status;
 
   /// Free-text category, prefilled in-app from the domain but opaque here.
   final String? category;