upgraded flutter and other fixes

lib/helpers/reaction_helper.dart

@@ -1,22 +1,53 @@
 class ReactionInfo {
   final String targetMessageId;
   final String emoji;
+  final String? reactionKey; // Lightweight key for deduplication: timestamp_senderPrefix
 
   ReactionInfo({
     required this.targetMessageId,
     required this.emoji,
+    this.reactionKey,
   });
 }
 
 class ReactionHelper {
   /// Parse reaction format: r:[messageId]:[emoji]
+  /// Supports both old format (full messageId) and new format (timestamp_senderPrefix)
   static ReactionInfo? parseReaction(String text) {
     final regex = RegExp(r'^r:([^:]+):(.+)$');
     final match = regex.firstMatch(text);
     if (match == null) return null;
+
+    final targetId = match.group(1)!;
+    final emoji = match.group(2)!;
+
+    // Extract reaction key for deduplication
+    // If targetId is in new format (timestamp_senderPrefix), use it directly
+    // Otherwise, extract timestamp from old format (timestamp_nameHash_textHash)
+    String? reactionKey;
+    if (targetId.contains('_')) {
+      final parts = targetId.split('_');
+      if (parts.length >= 2) {
+        // New format: timestamp_senderPrefix, or old format with at least timestamp
+        reactionKey = '${parts[0]}_${parts[1]}';
+      }
+    }
+
     return ReactionInfo(
-      targetMessageId: match.group(1)!,
-      emoji: match.group(2)!,
+      targetMessageId: targetId,
+      emoji: emoji,
+      reactionKey: reactionKey,
     );
   }
+
+  /// Generate a lightweight reaction key for a message
+  /// Format: r:[timestamp]_[senderPrefix]:[emoji]
+  static String buildReactionText(String timestamp, String senderPrefix, String emoji) {
+    return 'r:${timestamp}_$senderPrefix:$emoji';
+  }
+
+  /// Extract sender prefix from public key hex (first 8 chars)
+  static String getSenderPrefix(String senderKeyHex) {
+    return senderKeyHex.substring(0, 8);
+  }
 }