refactor(transactions): split shared port from broadcast review feature

lib/core/transactions/ was structured as a full feature inside core
(domain + application + presentation + ui), violating the rule that
core is infrastructure only. The cubit, screen, usecase, and
ReviewableTransaction aggregate were consumed solely by
lib/features/broadcast_signed_tx/.

Split: keep the shared primitives in core (Transaction entities,
TransactionPort, TransactionMapper) since electrum implements the port
and depends on the mapper; move review-specific concerns into the
broadcast_signed_tx feature.

Errors split per-layer: TransactionPortError in core (thrown by the
port adapter), TransactionReviewError in the feature (thrown by the
usecase, wrapping port errors at the boundary). The view renders
TransactionReviewError and unwraps the inner port error for granular
messaging — never sees a foreign error type.

Drop dead code: BuildTransactionUsecase had three execute methods —
executeFromTransaction was internal-only and executeFromWalletTransaction
was never called. Collapse to a single execute(). Drop unused
TransactionMapper.fromLiquidTx and the dead TransactionParseFailed
variant.

Rename per AGENTS.md naming: TransactionEntity -> ReviewableTransaction
(no Entity suffix), TransactionCubit -> TransactionReviewCubit,
TransactionScreen -> TransactionReviewView (it's an embedded widget,
not a routed screen). Folder layout per rule 14 — no single-file
subfolders.

Author: ethicnology

integration_test/sqlite_transactions_test.dart

@@ -1,5 +1,5 @@
 import 'package:bb_mobile/core/storage/sqlite_database.dart';
-import 'package:bb_mobile/core/transactions/domain/ports/transaction_port.dart';
+import 'package:bb_mobile/core/transactions/domain/transaction_port.dart';
 import 'package:bb_mobile/locator.dart';
 import 'package:bb_mobile/main.dart';
 import 'package:flutter_test/flutter_test.dart';

lib/core/electrum/adapters/drift_electrum_transaction_repository.dart

@@ -0,0 +1,22 @@
+import 'package:bb_mobile/core/electrum/domain/repositories/electrum_transaction_repository.dart';
+import 'package:bb_mobile/core/electrum/frameworks/drift/datasources/electrum_remote_datasource.dart';
+import 'package:bb_mobile/core/storage/tables/transactions_table.dart';
+import 'package:bb_mobile/core/utils/bitcoin_tx.dart';
+
+class DriftElectrumTransactionRepository
+    implements ElectrumTransactionRepository {
+  final ElectrumRemoteDatasource _datasource;
+
+  DriftElectrumTransactionRepository({
+    required ElectrumRemoteDatasource datasource,
+  }) : _datasource = datasource;
+
+  @override
+  Future<BitcoinTx> fetch({
+    required String serverUrl,
+    required String txid,
+  }) async {
+    final model = await _datasource.fetch(serverUrl: serverUrl, txid: txid);
+    return TransactionModelExtension.toEntity(model);
+  }
+}

lib/core/electrum/adapters/electrum_transaction_port_adapter.dart

@@ -0,0 +1,64 @@
+import 'package:bb_mobile/core/electrum/domain/ports/electrum_servers_port.dart';
+import 'package:bb_mobile/core/electrum/domain/ports/environment_port.dart';
+import 'package:bb_mobile/core/electrum/domain/repositories/electrum_transaction_repository.dart';
+import 'package:bb_mobile/core/electrum/domain/value_objects/electrum_environment.dart';
+import 'package:bb_mobile/core/electrum/domain/value_objects/electrum_server_network.dart';
+import 'package:bb_mobile/core/transactions/adapters/transaction_mapper.dart';
+import 'package:bb_mobile/core/transactions/domain/domain_errors.dart';
+import 'package:bb_mobile/core/transactions/domain/entities/transaction.dart';
+import 'package:bb_mobile/core/transactions/domain/transaction_port.dart';
+
+/// Adapter implementing [TransactionPort] for the Electrum module.
+///
+/// Iterates the configured Electrum servers in priority order, falling back
+/// on failure, then maps the parsed [BitcoinTx] into a [Transaction] domain
+/// entity. Surfaces failures as [TransactionPortError] so consumers never
+/// see electrum's error types.
+class ElectrumTransactionPortAdapter implements TransactionPort {
+  final ElectrumServersPort _serversPort;
+  final ElectrumTransactionRepository _repository;
+  final EnvironmentPort _environmentPort;
+
+  const ElectrumTransactionPortAdapter({
+    required ElectrumServersPort serversPort,
+    required ElectrumTransactionRepository repository,
+    required EnvironmentPort environmentPort,
+  }) : _serversPort = serversPort,
+       _repository = repository,
+       _environmentPort = environmentPort;
+
+  @override
+  Future<Transaction> fetch({required String txid}) async {
+    final environment = await _environmentPort.getEnvironment();
+    final network = ElectrumServerNetwork.fromEnvironment(
+      isTestnet: environment.isTestnet,
+      isLiquid: false,
+    );
+
+    final servers = await _serversPort.getServersToUse(network: network);
+    if (servers.isEmpty) {
+      throw TransactionPortError.noServersAvailable(
+        network: network.toString(),
+      );
+    }
+
+    Object? lastError;
+    for (final server in servers) {
+      try {
+        final bitcoinTx = await _repository.fetch(
+          serverUrl: server.url,
+          txid: txid,
+        );
+        return TransactionMapper.fromBitcoinTx(
+          bitcoinTx,
+          isTestnet: environment.isTestnet,
+        );
+      } catch (e) {
+        lastError = e;
+        continue;
+      }
+    }
+
+    throw TransactionPortError.fetchFailed(txid: txid, message: '$lastError');
+  }
+}

…ons/data/mappers/transaction_mapper.dart …actions/adapters/transaction_mapper.dartlib/core/transactions/data/mappers/transaction_mapper.dart renamed to lib/core/transactions/adapters/transaction_mapper.dart lib/core/transactions/data/mappers/transaction_mapper.dart renamed to lib/core/transactions/adapters/transaction_mapper.dart

@@ -1,14 +1,12 @@
 import 'dart:typed_data';
 
-import 'package:bb_mobile/core/transactions/domain/entity/bitcoin_transaction.dart';
-import 'package:bb_mobile/core/transactions/domain/entity/liquid_transaction.dart';
+import 'package:bb_mobile/core/transactions/domain/entities/bitcoin_transaction.dart';
 import 'package:bb_mobile/core/utils/bitcoin_tx.dart' as btc_utils;
-import 'package:bb_mobile/core/utils/liquid_tx.dart' as liq_utils;
 import 'package:bdk_dart/bdk.dart' as bdk;
 import 'package:convert/convert.dart';
 
-/// Maps between the existing utility classes ([BitcoinTx], [LiquidTx])
-/// and the new domain entities ([BitcoinTransaction], [LiquidTransaction]).
+/// Maps the BDK utility class [btc_utils.BitcoinTx] to the domain entity
+/// [BitcoinTransaction].
 class TransactionMapper {
   /// Convert a [btc_utils.BitcoinTx] utility class to a [BitcoinTransaction]
   /// domain entity.
@@ -26,7 +24,7 @@ class TransactionMapper {
       size: bitcoinTx.size.toInt(),
       vsize: bitcoinTx.vsize.toInt(),
       locktime: bitcoinTx.locktime,
-      inputs: bitcoinTx.vin.map((vin) => _mapBitcoinInput(vin)).toList(),
+      inputs: bitcoinTx.vin.map(_mapBitcoinInput).toList(),
       outputs: bitcoinTx.vout
           .asMap()
           .entries
@@ -38,25 +36,6 @@ class TransactionMapper {
     );
   }
 
-  /// Convert a [liq_utils.LiquidTx] utility class to a [LiquidTransaction]
-  /// domain entity.
-  static LiquidTransaction fromLiquidTx(liq_utils.LiquidTx liquidTx) {
-    return LiquidTransaction(
-      txid: liquidTx.txid,
-      version: liquidTx.version,
-      vsize: liquidTx.vsize.toInt(),
-      weight: liquidTx.weight.toInt(),
-      locktime: liquidTx.locktime,
-      feeSat: liquidTx.fee.toInt(),
-      inputs: liquidTx.vin.map((vin) => _mapLiquidInput(vin)).toList(),
-      outputs: liquidTx.vout
-          .asMap()
-          .entries
-          .map((entry) => _mapLiquidOutput(entry.value, entry.key))
-          .toList(),
-    );
-  }
-
   static BitcoinTxInput _mapBitcoinInput(btc_utils.TxVin vin) {
     return BitcoinTxInput(
       previousTxId: vin.txid,
@@ -91,28 +70,4 @@ class TransactionMapper {
       scriptPubKeyBytes: vout.scriptPubKey.bytes,
     );
   }
-
-  static LiquidTxInput _mapLiquidInput(liq_utils.LiquidTxVin vin) {
-    return LiquidTxInput(
-      previousTxId: vin.txid,
-      previousVout: vin.vout,
-      sequence: vin.sequence,
-      scriptSig: vin.scriptSig,
-      witness: vin.witness,
-      isPegin: vin.isPegin,
-    );
-  }
-
-  static LiquidTxOutput _mapLiquidOutput(
-    liq_utils.LiquidTxVout vout,
-    int index,
-  ) {
-    return LiquidTxOutput(
-      valueSat: vout.value?.toInt() ?? 0,
-      index: index,
-      scriptPubKeyHex: vout.scriptPubKey,
-      asset: vout.asset,
-      nonce: vout.nonce,
-    );
-  }
 }

lib/core/transactions/application/build_transaction_usecase.dart

@@ -0,0 +1,23 @@
+import 'package:freezed_annotation/freezed_annotation.dart';
+
+part 'domain_errors.freezed.dart';
+
+/// Errors thrown by implementations of [TransactionPort].
+///
+/// Port-layer concerns only — fetching a parsed transaction from an
+/// external source. Higher layers map these into their own domain errors
+/// at the boundary so the port's error type never leaks upward.
+@freezed
+sealed class TransactionPortError with _$TransactionPortError {
+  /// Failed to fetch the transaction across all configured servers.
+  const factory TransactionPortError.fetchFailed({
+    required String txid,
+    String? message,
+  }) = TransactionPortFetchFailed;
+
+  /// No servers are available for the requested network.
+  const factory TransactionPortError.noServersAvailable({String? network}) =
+      TransactionPortNoServersAvailable;
+
+  const TransactionPortError._();
+}

lib/core/transactions/domain/domain_errors.dart

@@ -1,4 +1,4 @@
-import 'package:bb_mobile/core/transactions/domain/entity/transaction.dart';
+import 'package:bb_mobile/core/transactions/domain/entities/transaction.dart';
 
 /// Concrete Bitcoin transaction implementing the abstract [Transaction].
 class BitcoinTransaction extends Transaction {

…s/domain/entity/bitcoin_transaction.dart …domain/entities/bitcoin_transaction.dartlib/core/transactions/domain/entity/bitcoin_transaction.dart renamed to lib/core/transactions/domain/entities/bitcoin_transaction.dart lib/core/transactions/domain/entity/bitcoin_transaction.dart renamed to lib/core/transactions/domain/entities/bitcoin_transaction.dart

@@ -1,4 +1,4 @@
-import 'package:bb_mobile/core/transactions/domain/entity/transaction.dart';
+import 'package:bb_mobile/core/transactions/domain/entities/transaction.dart';
 
 /// Concrete Liquid transaction implementing the abstract [Transaction].
 ///