feat(plantare): PlantareTransport foundation in commons_core

The bilateral signed Plantaré's transport layer — the "formulario
bilateral firmado" from plantare-bilateral.md — as a new interface
alongside the other *Transport contracts, on the shared NostrConnection.

- PlantarePledge: the canonical, byte-stable core (debtor/creditor keys,
  seed label, return kind, dates) plus the two Schnorr stubs. Any edit
  changes the signing hash, so an accept is always over an immutable
  payload.
- PlantareCrypto: BIP-340 signing/verification over SHA-256 of the core,
  reusing the same primitive Nostr uses for events — a pubkey both
  identifies a party and verifies their stub.
- PlantareTransport + NostrPlantareTransport: propose → accept →
  counter-sign (and decline), private end-to-end. Rides the existing
  NIP-17 gift wrap carrying a tagged JSON payload, so the relay sees only
  ciphertext and an ephemeral author. Offline QR/NFC is the same payload
  without a relay.
- Message transport skips Plantaré payloads on the shared kind-1059
  channel (and vice-versa), so moves never surface as chat.

Tests: pure pledge/crypto + full handshake over a hermetic relay,
including no-leak and no-chat-bleed. commons_core 101/101 green.

packages/commons_core/lib/commons_core.dart

@@ -21,6 +21,7 @@ export 'src/social/nostr/nostr_sync_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_plantare_transport.dart';
 export 'src/social/nostr/nostr_profile_transport.dart';
 export 'src/social/nostr/nostr_rating_transport.dart';
 export 'src/social/nostr/nostr_report_transport.dart';
@@ -28,6 +29,8 @@ export 'src/social/nostr/nostr_trust_transport.dart';
 export 'src/social/nostr/relay_pool.dart';
 export 'src/social/offer.dart';
 export 'src/social/offer_transport.dart';
+export 'src/social/plantare.dart';
+export 'src/social/plantare_transport.dart';
 export 'src/social/profile_transport.dart';
 export 'src/social/rating.dart';
 export 'src/social/rating_transport.dart';

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

@@ -1,9 +1,11 @@
 import 'dart:async';
+import 'dart:convert';
 
 import 'package:nostr/nostr.dart' as nostr;
 
 import '../message_transport.dart';
 import 'nostr_channel.dart';
+import 'nostr_plantare_transport.dart';
 
 /// NIP-17 private-DM backend for [MessageTransport], on the shared
 /// [NostrConnection]. The gift-wrap onion (rumor kind 14 → seal kind 13 → wrap
@@ -53,6 +55,7 @@ class NostrMessageTransport implements MessageTransport {
         giftWrap: wrap,
         recipientSecretKey: _conn.privateKeyHex,
       );
+      if (_isPlantare(rumor.content)) return null; // handled by PlantareTransport
       return PrivateMessage(
         fromPubkey: rumor.pubkey,
         text: rumor.content,
@@ -63,6 +66,19 @@ class NostrMessageTransport implements MessageTransport {
     }
   }
 
+  /// A Plantaré move gift-wrapped on the SAME kind-1059 channel is not chat —
+  /// it's a tagged JSON payload handled by [NostrPlantareTransport]. Skip it so
+  /// it never surfaces as a message.
+  static bool _isPlantare(String content) {
+    try {
+      final decoded = jsonDecode(content);
+      return decoded is Map &&
+          decoded['t'] == NostrPlantareTransport.wireTag;
+    } catch (_) {
+      return false; // ordinary text
+    }
+  }
+
   @override
   Future<void> close() => _conn.close();
 }

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

@@ -0,0 +1,141 @@
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:nostr/nostr.dart' as nostr;
+
+import '../plantare.dart';
+import '../plantare_transport.dart';
+import 'nostr_channel.dart';
+
+/// NIP-17 private-DM backend for [PlantareTransport], on the shared channel.
+///
+/// A Plantaré move rides the same gift-wrapped, NIP-44-encrypted envelope as a
+/// DM (rumor kind 14 → seal kind 13 → wrap kind 1059 signed by an ephemeral
+/// key), carrying a canonical JSON payload instead of chat text. This is the
+/// least new surface — it reuses the vetted onion and the existing connection —
+/// and gives the same metadata privacy (the relay sees only ciphertext and an
+/// ephemeral author). The payload is tagged [wireTag] so a plain-chat inbox can
+/// tell the two apart and skip these (and vice-versa).
+class NostrPlantareTransport implements PlantareTransport {
+  NostrPlantareTransport(this._conn);
+
+  final NostrChannel _conn;
+
+  static const kindGiftWrap = 1059;
+
+  /// Discriminator on the encrypted payload so a co-tenant chat inbox on the
+  /// same kind-1059 channel can ignore Plantaré moves.
+  static const wireTag = 'plantare/v1';
+
+  @override
+  Future<void> propose(PlantarePledge pledge) =>
+      _sendPledge(PlantareMessageKind.proposed, pledge);
+
+  @override
+  Future<void> accept(PlantarePledge pledge) =>
+      _sendPledge(PlantareMessageKind.accepted, pledge);
+
+  @override
+  Future<void> decline({
+    required String toPubkey,
+    required String pledgeId,
+    String reason = '',
+  }) =>
+      _sendTo(toPubkey, <String, Object?>{
+        't': wireTag,
+        'kind': PlantareMessageKind.declined.name,
+        'pledgeId': pledgeId,
+        'reason': reason,
+      });
+
+  @override
+  Stream<PlantareEnvelope> incoming() => _conn
+      .subscribe(
+        nostr.Filter(kinds: const [kindGiftWrap], pTags: [_conn.publicKeyHex]),
+      )
+      .asyncMap(_unwrap)
+      .where((e) => e != null)
+      .cast<PlantareEnvelope>();
+
+  /// Collects the incoming Plantaré moves up to EOSE (tests/one-shot).
+  Future<List<PlantareEnvelope>> incomingUntilEose() async {
+    final wraps = await _conn.reqOnce(
+      nostr.Filter(kinds: const [kindGiftWrap], pTags: [_conn.publicKeyHex]),
+    );
+    final out = <PlantareEnvelope>[];
+    for (final w in wraps) {
+      final e = await _unwrap(w);
+      if (e != null) out.add(e);
+    }
+    return out;
+  }
+
+  Future<void> _sendPledge(
+    PlantareMessageKind kind,
+    PlantarePledge pledge,
+  ) async {
+    final to = pledge.counterpartyOf(_conn.publicKeyHex);
+    if (to == null) {
+      throw ArgumentError('this identity is neither party to the pledge');
+    }
+    await _sendTo(to, <String, Object?>{
+      't': wireTag,
+      'kind': kind.name,
+      'pledge': pledge.toJson(),
+    });
+  }
+
+  Future<void> _sendTo(String toPubkey, Map<String, Object?> payload) async {
+    final wrap = await nostr.DirectMessage.create(
+      message: jsonEncode(payload),
+      authorSecretKey: _conn.privateKeyHex,
+      recipientPubkey: toPubkey,
+    );
+    final r = await _conn.publish(wrap);
+    if (!r.accepted) throw StateError('relay rejected plantare: ${r.message}');
+  }
+
+  Future<PlantareEnvelope?> _unwrap(nostr.Event wrap) async {
+    final nostr.Event rumor;
+    try {
+      rumor = await nostr.DirectMessage.parse(
+        giftWrap: wrap,
+        recipientSecretKey: _conn.privateKeyHex,
+      );
+    } catch (_) {
+      return null; // not for us / wrong key / tampered
+    }
+    final Object? decoded;
+    try {
+      decoded = jsonDecode(rumor.content);
+    } catch (_) {
+      return null; // plain chat, not JSON — not ours
+    }
+    if (decoded is! Map || decoded['t'] != wireTag) return null;
+    try {
+      final kind = PlantareMessageKind.values.byName(decoded['kind'] as String);
+      switch (kind) {
+        case PlantareMessageKind.proposed:
+        case PlantareMessageKind.accepted:
+          return PlantareEnvelope(
+            kind: kind,
+            fromPubkey: rumor.pubkey,
+            pledge:
+                PlantarePledge.fromJson((decoded['pledge'] as Map).cast()),
+          );
+        case PlantareMessageKind.declined:
+          return PlantareEnvelope(
+            kind: kind,
+            fromPubkey: rumor.pubkey,
+            pledgeId: decoded['pledgeId'] as String?,
+            reason: (decoded['reason'] as String?) ?? '',
+          );
+      }
+    } catch (_) {
+      return null; // malformed payload
+    }
+  }
+
+  @override
+  Future<void> close() => _conn.close();
+}

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

@@ -0,0 +1,264 @@
+import 'dart:convert';
+
+import 'package:cryptography/cryptography.dart';
+import 'package:equatable/equatable.dart';
+import 'package:nostr/nostr.dart' show Schnorr;
+
+/// How a Plantaré is promised back, mirroring the paper form's checkboxes
+/// (BAH-Semillero v4.0). [similar] means the default: open-pollinated · non-GMO
+/// · organically grown — surface that meaning, not just the word. [workHours] is
+/// time-as-currency ("un trabajo de N horas"). [other] is anything else, carried
+/// in the free-text description. Generic core type — no seed specifics beyond the
+/// name.
+enum ReturnKind { similar, workHours, other }
+
+/// The three moves of the bilateral handshake: a proposer signs and [proposed],
+/// the counterparty counter-signs and [accepted], or [declined] it.
+enum PlantareMessageKind { proposed, accepted, declined }
+
+/// One bilateral Plantaré — the digital form of the paper's two matching signed
+/// stubs ("partida doble"). Both parties end up holding the *same* record, each
+/// signed by both, so either can prove "recibí X, devolveré una cantidad similar
+/// antes de la fecha Y".
+///
+/// The debtor received the seed and owes a return; the creditor gave it. Which
+/// side is which is carried by [debtorKey]/[creditorKey], so no separate
+/// direction field is needed. The two signatures cover the *immutable core* —
+/// everything except the signatures themselves ([canonicalString]) — so any edit
+/// after proposing changes the [pledgeId] and forces a fresh proposal (accept is
+/// over an immutable hash).
+///
+/// Generic core type: it knows keys, a human seed [label] and a promise; it does
+/// NOT know the app's local `Variety`/`Movement` ids (those live app-side).
+class PlantarePledge extends Equatable {
+  const PlantarePledge({
+    required this.pledgeId,
+    required this.debtorKey,
+    required this.creditorKey,
+    required this.madeOn,
+    this.label,
+    this.owedDescription,
+    this.returnKind = ReturnKind.similar,
+    this.workHours,
+    this.dueBy,
+    this.debtorSignature,
+    this.creditorSignature,
+  });
+
+  /// Stable id (proposer's UUIDv7). Part of the signed core, so it also pins the
+  /// exact terms: a changed pledge is a different id.
+  final String pledgeId;
+
+  /// Pubkey (hex) of who received the seed and owes a return.
+  final String debtorKey;
+
+  /// Pubkey (hex) of who gave the seed.
+  final String creditorKey;
+
+  /// When the promise was made.
+  final DateTime madeOn;
+
+  /// Human name of the seed the promise is about (the counterparty may not have
+  /// it catalogued, so we carry the label, not a local id). Optional.
+  final String? label;
+
+  /// What's promised back in the grower's own words — backs [ReturnKind.other]
+  /// and enriches the others.
+  final String? owedDescription;
+
+  final ReturnKind returnKind;
+
+  /// Hours for [ReturnKind.workHours] (time-as-currency). Null otherwise.
+  final double? workHours;
+
+  /// Optional return-by date — a gentle reminder matched to cultivation cycles,
+  /// not a deadline.
+  final DateTime? dueBy;
+
+  /// Schnorr signature (hex) of the debtor over [signingHash]. Null until signed.
+  final String? debtorSignature;
+
+  /// Schnorr signature (hex) of the creditor over [signingHash]. Null until
+  /// signed.
+  final String? creditorSignature;
+
+  /// Whether both parties have signed — a fully-closed, provable deal.
+  bool get isFullySigned =>
+      debtorSignature != null && creditorSignature != null;
+
+  /// The other party to [me] (whichever key isn't mine), or null if [me] is
+  /// neither — used by the transport to route without a separate recipient arg.
+  String? counterpartyOf(String me) {
+    if (me == debtorKey) return creditorKey;
+    if (me == creditorKey) return debtorKey;
+    return null;
+  }
+
+  /// The immutable core, serialized deterministically (sorted keys, no
+  /// signatures). Both parties sign the hash of exactly this string, so it must
+  /// be byte-stable across devices and versions.
+  String canonicalString() => jsonEncode(<String, Object?>{
+        'v': 1,
+        'pledgeId': pledgeId,
+        'debtorKey': debtorKey,
+        'creditorKey': creditorKey,
+        'madeOn': madeOn.millisecondsSinceEpoch,
+        'label': label,
+        'owedDescription': owedDescription,
+        'returnKind': returnKind.name,
+        'workHours': workHours,
+        'dueBy': dueBy?.millisecondsSinceEpoch,
+      });
+
+  PlantarePledge copyWith({
+    String? debtorSignature,
+    String? creditorSignature,
+  }) =>
+      PlantarePledge(
+        pledgeId: pledgeId,
+        debtorKey: debtorKey,
+        creditorKey: creditorKey,
+        madeOn: madeOn,
+        label: label,
+        owedDescription: owedDescription,
+        returnKind: returnKind,
+        workHours: workHours,
+        dueBy: dueBy,
+        debtorSignature: debtorSignature ?? this.debtorSignature,
+        creditorSignature: creditorSignature ?? this.creditorSignature,
+      );
+
+  /// Full wire form (the canonical core plus whatever signatures exist so far).
+  Map<String, Object?> toJson() => <String, Object?>{
+        'pledgeId': pledgeId,
+        'debtorKey': debtorKey,
+        'creditorKey': creditorKey,
+        'madeOn': madeOn.millisecondsSinceEpoch,
+        'label': label,
+        'owedDescription': owedDescription,
+        'returnKind': returnKind.name,
+        'workHours': workHours,
+        'dueBy': dueBy?.millisecondsSinceEpoch,
+        'debtorSignature': debtorSignature,
+        'creditorSignature': creditorSignature,
+      };
+
+  static PlantarePledge fromJson(Map<String, Object?> json) => PlantarePledge(
+        pledgeId: json['pledgeId']! as String,
+        debtorKey: json['debtorKey']! as String,
+        creditorKey: json['creditorKey']! as String,
+        madeOn:
+            DateTime.fromMillisecondsSinceEpoch((json['madeOn']! as num).toInt()),
+        label: json['label'] as String?,
+        owedDescription: json['owedDescription'] as String?,
+        returnKind: ReturnKind.values.byName(json['returnKind'] as String),
+        workHours: (json['workHours'] as num?)?.toDouble(),
+        dueBy: json['dueBy'] == null
+            ? null
+            : DateTime.fromMillisecondsSinceEpoch((json['dueBy']! as num).toInt()),
+        debtorSignature: json['debtorSignature'] as String?,
+        creditorSignature: json['creditorSignature'] as String?,
+      );
+
+  @override
+  List<Object?> get props => [
+        pledgeId,
+        debtorKey,
+        creditorKey,
+        madeOn,
+        label,
+        owedDescription,
+        returnKind,
+        workHours,
+        dueBy,
+        debtorSignature,
+        creditorSignature,
+      ];
+}
+
+/// Signing/verification over a [PlantarePledge]'s canonical core. Each signature
+/// is a BIP-340 Schnorr signature (the same primitive Nostr uses for events)
+/// over the SHA-256 of [PlantarePledge.canonicalString], so a Nostr pubkey both
+/// identifies a party and verifies their stub.
+abstract final class PlantareCrypto {
+  /// The 32-byte (hex) message both parties sign: SHA-256 of the canonical core.
+  static Future<String> signingHash(PlantarePledge pledge) async {
+    final digest =
+        await Sha256().hash(utf8.encode(pledge.canonicalString()));
+    return _toHex(digest.bytes);
+  }
+
+  /// Signs [pledge]'s core with [secretKeyHex]; returns the hex signature. The
+  /// caller stores it on the debtor or creditor slot depending on which key it
+  /// belongs to.
+  static Future<String> sign(
+    PlantarePledge pledge,
+    String secretKeyHex,
+  ) async =>
+      Schnorr.sign(secretKey: secretKeyHex, message: await signingHash(pledge));
+
+  /// Verifies [signature] was made over [pledge]'s core by [publicKeyHex].
+  static Future<bool> verify(
+    PlantarePledge pledge,
+    String publicKeyHex,
+    String signature,
+  ) async {
+    try {
+      return Schnorr.verify(
+        publicKey: publicKeyHex,
+        message: await signingHash(pledge),
+        signature: signature,
+      );
+    } catch (_) {
+      return false; // malformed key/sig → not valid
+    }
+  }
+
+  /// Whether both stubs verify against their respective keys — a provably closed
+  /// deal, the strong anchor for a rating.
+  static Future<bool> verifyBoth(PlantarePledge pledge) async {
+    final d = pledge.debtorSignature;
+    final c = pledge.creditorSignature;
+    if (d == null || c == null) return false;
+    return await verify(pledge, pledge.debtorKey, d) &&
+        await verify(pledge, pledge.creditorKey, c);
+  }
+
+  static String _toHex(List<int> bytes) {
+    final sb = StringBuffer();
+    for (final b in bytes) {
+      sb.write(b.toRadixString(16).padLeft(2, '0'));
+    }
+    return sb.toString();
+  }
+}
+
+/// One decrypted Plantaré move handed to the app: a [proposed] or [accepted]
+/// pledge, or a [declined] notice. [fromPubkey] is the authenticated sender
+/// (from the inner rumor, not the gift-wrap's ephemeral key).
+class PlantareEnvelope extends Equatable {
+  const PlantareEnvelope({
+    required this.kind,
+    required this.fromPubkey,
+    this.pledge,
+    this.pledgeId,
+    this.reason = '',
+  });
+
+  final PlantareMessageKind kind;
+  final String fromPubkey;
+
+  /// The pledge for [PlantareMessageKind.proposed]/[accepted]; null for a
+  /// decline, which carries only [pledgeId] and [reason].
+  final PlantarePledge? pledge;
+
+  /// The declined pledge's id (decline carries no full pledge).
+  final String? pledgeId;
+  final String reason;
+
+  /// The pledge id this envelope concerns, from whichever field holds it.
+  String? get id => pledge?.pledgeId ?? pledgeId;
+
+  @override
+  List<Object?> get props => [kind, fromPubkey, pledge, pledgeId, reason];
+}

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

@@ -0,0 +1,37 @@
+import 'plantare.dart';
+
+/// The bilateral-Plantaré contract over the shared connection: propose a signed
+/// stub, counter-sign it, or decline. Unlike ratings/certifications (public
+/// signed events), a Plantaré is PRIVATE to the two parties, so — like DMs and
+/// sync — it is encrypted end-to-end. The recipient is inferred from the
+/// pledge's debtor/creditor keys (whichever isn't this identity), so there is no
+/// separate address argument.
+///
+/// Handshake: propose → accept → counter-sign. A proposes (A's signature only,
+/// encrypted to B); B reviews and accepts (adds B's signature), sending the
+/// doubly-signed copy back; both persist the identical, fully-signed row.
+///
+/// Channel-agnostic: the default backend rides the existing NIP-17 encrypted DM,
+/// but the same canonical payload works device-to-device over QR/NFC (offline
+/// must fully work; relays only enrich).
+abstract interface class PlantareTransport {
+  /// Sends a signed proposal (my signature only) to the pledge's counterparty.
+  Future<void> propose(PlantarePledge pledge);
+
+  /// Counter-signs a received proposal and sends the fully-signed copy back.
+  Future<void> accept(PlantarePledge pledge);
+
+  /// Declines a received proposal, notifying its proposer [toPubkey], optionally
+  /// with a short [reason]. (A decline carries no pledge, so unlike propose/
+  /// accept the recipient can't be inferred and is passed explicitly.)
+  Future<void> decline({
+    required String toPubkey,
+    required String pledgeId,
+    String reason,
+  });
+
+  /// Incoming proposals / accepts / declines addressed to this identity, live.
+  Stream<PlantareEnvelope> incoming();
+
+  Future<void> close();
+}