diff --git a/lib/src/registry/data_operation_registry.dart b/lib/src/registry/data_operation_registry.dart
index c5574e0..a0533a7 100644
--- a/lib/src/registry/data_operation_registry.dart
+++ b/lib/src/registry/data_operation_registry.dart
@@ -318,6 +318,26 @@ class DataOperationRegistry {
           );
         }
 
+        // Business Logic Check: Ensure a user can only have one engagement
+        // per headline to prevent duplicate reactions or comments.
+        final engagementRepository = context.read<DataRepository<Engagement>>();
+        final existingEngagements = await engagementRepository.readAll(
+          filter: {
+            'userId': authenticatedUser.id,
+            'entityId': engagementToCreate.entityId,
+            'entityType': engagementToCreate.entityType.name,
+          },
+        );
+
+        if (existingEngagements.items.isNotEmpty) {
+          _log.warning(
+            'User ${authenticatedUser.id} attempted to create a second engagement for entity ${engagementToCreate.entityId}.',
+          );
+          throw const ConflictException(
+            'An engagement for this item already exists.',
+          );
+        }
+
         // Limit Check: Delegate to the centralized service.
         await userActionLimitService.checkEngagementCreationLimit(
           user: authenticatedUser,
diff --git a/lib/src/services/default_user_action_limit_service.dart b/lib/src/services/default_user_action_limit_service.dart
index ca72890..9674eb1 100644
--- a/lib/src/services/default_user_action_limit_service.dart
+++ b/lib/src/services/default_user_action_limit_service.dart
@@ -265,24 +265,35 @@ class DefaultUserActionLimitService implements UserActionLimitService {
       );
     }
 
-    // Count all engagements in the last 24 hours for the reaction limit.
-    final twentyFourHoursAgo = DateTime.now().subtract(
-      const Duration(hours: 24),
-    );
-    final reactionCount = await _engagementRepository.count(
-      filter: {
-        'userId': user.id,
-        'createdAt': {r'$gte': twentyFourHoursAgo.toIso8601String()},
-      },
-    );
+    // --- 1. Check Reaction Limit (only if a reaction is present) ---
+    if (engagement.reaction != null) {
+      final reactionsLimit = limits.reactionsPerDay[user.appRole];
+      if (reactionsLimit == null) {
+        throw StateError(
+          'Reactions per day limit not configured for role: ${user.appRole}',
+        );
+      }
 
-    if (reactionCount >= reactionsLimit) {
-      _log.warning(
-        'User ${user.id} exceeded reactions per day limit: $reactionsLimit.',
+      // Count engagements with reactions in the last 24 hours.
+      final twentyFourHoursAgo = DateTime.now().subtract(
+        const Duration(hours: 24),
       );
-      throw const ForbiddenException(
-        'You have reached your daily limit for reactions.',
+      final reactionCount = await _engagementRepository.count(
+        filter: {
+          'userId': user.id,
+          'reaction': {r'$exists': true, r'$ne': null},
+          'createdAt': {r'$gte': twentyFourHoursAgo.toIso8601String()},
+        },
       );
+
+      if (reactionCount >= reactionsLimit) {
+        _log.warning(
+          'User ${user.id} exceeded reactions per day limit: $reactionsLimit.',
+        );
+        throw const ForbiddenException(
+          'You have reached your daily limit for reactions.',
+        );
+      }
     }
 
     // --- 2. Check Comment Limit (only if a comment is present) ---
@@ -295,6 +306,9 @@ class DefaultUserActionLimitService implements UserActionLimitService {
       }
 
       // Count engagements with comments in the last 24 hours.
+      final twentyFourHoursAgo = DateTime.now().subtract(
+        const Duration(hours: 24),
+      );
       final commentCount = await _engagementRepository.count(
         filter: {
           'userId': user.id,
diff --git a/pubspec.lock b/pubspec.lock
index 6fc6de9..b5fa979 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -181,8 +181,8 @@ packages:
     dependency: "direct main"
     description:
       path: "."
-      ref: "8bae6eb17369b76f72961870a22ee13d3073fa61"
-      resolved-ref: "8bae6eb17369b76f72961870a22ee13d3073fa61"
+      ref: e66e076572bd326e50e9d5286ef5059ff658ed65
+      resolved-ref: e66e076572bd326e50e9d5286ef5059ff658ed65
       url: "https://github.com/flutter-news-app-full-source-code/core.git"
     source: git
     version: "1.3.1"
diff --git a/pubspec.yaml b/pubspec.yaml
index a8dfd86..951b990 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -62,7 +62,7 @@ dependency_overrides:
   core:
     git:
       url: https://github.com/flutter-news-app-full-source-code/core.git
-      ref: 8bae6eb17369b76f72961870a22ee13d3073fa61
+      ref: e66e076572bd326e50e9d5286ef5059ff658ed65
   data_mongodb:
     git:
       url: https://github.com/flutter-news-app-full-source-code/data-mongodb.git