fix(wallet): restore tx explorer fallback when tx pattern is missing

lib/shared/utils/utils.dart

@@ -190,16 +190,22 @@ Map<String, dynamic>? rat2fract(Rational? rat, [bool toLog = true]) {
 String getTxExplorerUrl(Coin coin, String txHash) {
   final String explorerUrl = coin.explorerUrl;
   final String explorerTxUrl = coin.explorerTxUrl;
-  if (explorerUrl.isEmpty || explorerTxUrl.isEmpty) return '';
+  if (explorerUrl.isEmpty) return '';
 
   final hash =
       coin.type == CoinType.tendermint || coin.type == CoinType.tendermintToken
       ? txHash.toUpperCase()
       : txHash;
 
-  return coin.need0xPrefixForTxHash && !hash.startsWith('0x')
-      ? '$explorerUrl${explorerTxUrl}0x$hash'
-      : '$explorerUrl$explorerTxUrl$hash';
+  final normalizedHash = coin.need0xPrefixForTxHash && !hash.startsWith('0x')
+      ? '0x$hash'
+      : hash;
+
+  if (explorerTxUrl.isEmpty) {
+    return '$explorerUrl$normalizedHash';
+  }
+
+  return '$explorerUrl$explorerTxUrl$normalizedHash';
 }
 
 String getAddressExplorerUrl(Coin coin, String address) {

test_units/main.dart

@@ -31,6 +31,7 @@ import 'tests/balance_utils/compute_wallet_total_usd_test.dart';
 import 'tests/utils/convert_double_to_string_test.dart';
 import 'tests/utils/convert_fract_rat_test.dart';
 import 'tests/utils/double_to_string_test.dart';
+import 'tests/utils/explorer_url_test.dart';
 import 'tests/utils/get_fiat_amount_tests.dart';
 import 'tests/utils/get_usd_balance_test.dart';
 import 'tests/utils/ipfs_gateway_manager_test.dart';
@@ -69,6 +70,7 @@ void main() {
     testUsdBalanceFormatter();
     testGetFiatAmount();
     testCustomDoubleToString();
+    testExplorerUrlHelpers();
     testRatToFracAndViseVersa();
 
     testDoubleToString();

test_units/tests/utils/explorer_url_test.dart

@@ -0,0 +1,78 @@
+import 'package:komodo_defi_types/komodo_defi_types.dart';
+import 'package:test/test.dart';
+import 'package:web_dex/model/coin.dart';
+import 'package:web_dex/model/coin_type.dart';
+import 'package:web_dex/shared/utils/utils.dart';
+
+void testExplorerUrlHelpers() {
+  test(
+    'getTxExplorerUrl falls back to base explorer when tx pattern is empty',
+    () {
+      final coin = _coinWithExplorer(
+        explorerUrl: 'https://explorer.example/tx/',
+        explorerTxUrl: '',
+      );
+
+      expect(
+        getTxExplorerUrl(coin, 'abc123'),
+        'https://explorer.example/tx/abc123',
+      );
+    },
+  );
+
+  test(
+    'getTxExplorerUrl keeps 0x prefix behavior on base explorer fallback',
+    () {
+      final coin = _coinWithExplorer(
+        explorerUrl: 'https://etherscan.io/tx/',
+        explorerTxUrl: '',
+        protocolType: 'ERC20',
+        type: CoinType.erc20,
+      );
+
+      expect(
+        getTxExplorerUrl(coin, 'deadbeef'),
+        'https://etherscan.io/tx/0xdeadbeef',
+      );
+    },
+  );
+}
+
+Coin _coinWithExplorer({
+  required String explorerUrl,
+  required String explorerTxUrl,
+  String protocolType = 'UTXO',
+  CoinType type = CoinType.utxo,
+}) {
+  final assetId = AssetId(
+    id: 'TEST',
+    name: 'Test Coin',
+    parentId: null,
+    symbol: AssetSymbol(assetConfigId: 'TEST'),
+    derivationPath: null,
+    chainId: AssetChainId(chainId: 0),
+    subClass: CoinSubClass.utxo,
+  );
+
+  return Coin(
+    type: type,
+    abbr: 'TEST',
+    id: assetId,
+    name: 'Test Coin',
+    logoImageUrl: null,
+    isCustomCoin: false,
+    explorerUrl: explorerUrl,
+    explorerTxUrl: explorerTxUrl,
+    explorerAddressUrl: '',
+    protocolType: protocolType,
+    protocolData: ProtocolData(platform: '', contractAddress: ''),
+    isTestCoin: false,
+    coingeckoId: null,
+    fallbackSwapContract: null,
+    priority: 0,
+    state: CoinState.inactive,
+    walletOnly: false,
+    mode: CoinMode.standard,
+    swapContractAddress: null,
+  );
+}