fix(coins): resolve metadata race during concurrent coin activations

lib/bloc/coins_bloc/coins_bloc.dart

@@ -549,8 +549,20 @@ class CoinsBloc extends Bloc<CoinsEvent, CoinsState> {
       );
     }
 
+    // Batch-write all asset IDs to wallet metadata in a single call before
+    // launching parallel activations. This avoids N concurrent read-modify-write
+    // cycles on the same metadata key which caused last-write-wins data loss.
+    await _coinsRepo.addAssetsToWalletMetadata(
+      coinsToActivate.map((asset) => asset.id),
+    );
+
     final enableFutures = coinsToActivate
-        .map((asset) => _coinsRepo.activateAssetsSync([asset]))
+        .map(
+          (asset) => _coinsRepo.activateAssetsSync(
+            [asset],
+            addToWalletMetadata: false,
+          ),
+        )
         .toList();
 
     // Ignore the return type here and let the broadcast handle the state updates as

lib/bloc/coins_bloc/coins_repo.dart

@@ -581,6 +581,13 @@ class CoinsRepo {
     }
   }
 
+  /// Adds the given assets (and their parent coins) to wallet metadata.
+  ///
+  /// This is exposed so callers can batch-write metadata before launching
+  /// parallel activations with `addToWalletMetadata: false`.
+  Future<void> addAssetsToWalletMetadata(Iterable<AssetId> assets) =>
+      _addAssetsToWalletMetdata(assets);
+
   Future<void> _addAssetsToWalletMetdata(Iterable<AssetId> assets) async {
     final parentIds = <String>{};
     for (final assetId in assets) {

lib/model/kdf_auth_metadata_extension.dart

@@ -98,41 +98,35 @@ extension KdfAuthMetadataExtension on KomodoDefiSdk {
 
   /// Adds new coin/asset IDs to the current user's activated coins list.
   ///
-  /// This method merges the provided [coins] with the existing activated coins,
-  /// ensuring no duplicates. The merged list is then stored in user metadata.
+  /// This method atomically merges the provided [coins] with the existing
+  /// activated coins, ensuring no duplicates and no lost writes under
+  /// concurrent calls.
   ///
-  /// If no user is currently signed in, the operation will complete but have no effect.
+  /// If no user is currently signed in, the operation will throw.
   ///
   /// [coins] - An iterable of coin/asset configuration IDs to add.
   Future<void> addActivatedCoins(Iterable<String> coins) async {
-    final user = await auth.currentUser;
-    final existingCoins = user == null
-        ? <String>[]
-        : user.metadata.valueOrNull<List<String>>('activated_coins') ??
-              <String>[];
-
-    final mergedCoins = <dynamic>{...existingCoins, ...coins}.toList();
-    await auth.setOrRemoveActiveUserKeyValue('activated_coins', mergedCoins);
+    await auth.updateActiveUserKeyValue('activated_coins', (current) {
+      final existing = (current as List<dynamic>?)?.cast<String>() ?? [];
+      return <String>{...existing, ...coins}.toList();
+    });
   }
 
   /// Removes specified coin/asset IDs from the current user's activated coins list.
   ///
-  /// This method removes all occurrences of the provided [coins] from the user's
-  /// activated coins list and updates the stored metadata.
+  /// This method atomically removes all occurrences of the provided [coins]
+  /// from the user's activated coins list, ensuring no lost writes under
+  /// concurrent calls.
   ///
-  /// If no user is currently signed in, the operation will complete but have no effect.
+  /// If no user is currently signed in, the operation will throw.
   ///
   /// [coins] - A list of coin/asset configuration IDs to remove.
   Future<void> removeActivatedCoins(List<String> coins) async {
-    final user = await auth.currentUser;
-    final existingCoins = user == null
-        ? <String>[]
-        : List<String>.from(
-            user.metadata.valueOrNull<List<String>>('activated_coins') ?? [],
-          );
-
-    existingCoins.removeWhere((coin) => coins.contains(coin));
-    await auth.setOrRemoveActiveUserKeyValue('activated_coins', existingCoins);
+    await auth.updateActiveUserKeyValue('activated_coins', (current) {
+      final existing = (current as List<dynamic>?)?.cast<String>() ?? [];
+      final updated = existing.where((c) => !coins.contains(c)).toList();
+      return updated.isEmpty ? null : updated;
+    });
   }
 
   /// Sets the seed backup confirmation status for the current user.