Refactor message retrieval logic to improve pagination and ordering

- Update GetMessages function to ensure that when a limit is specified, the most recent messages are retrieved in descending order and then reversed for chronological output.
- Adjust pagination handling to apply a large limit when only an offset is provided, maintaining clarity in message retrieval.
- Enhance query ordering to prioritize message creation time and sequence for consistent results.

agent/store/xun/message.go

@@ -140,20 +140,24 @@ func (store *Xun) GetMessages(chatID string, filter types.MessageFilter) ([]*typ
 		qb.Where("type", filter.Type)
 	}
 
-	// Apply pagination (MySQL requires LIMIT when using OFFSET)
+	// When a Limit is specified we want the N most-recent messages (not the
+	// N oldest).  Strategy: query DESC to get the latest rows, then reverse
+	// the slice so the caller receives them in chronological (ASC) order.
+	needReverse := false
 	if filter.Limit > 0 {
 		qb.Limit(filter.Limit)
 		if filter.Offset > 0 {
 			qb.Offset(filter.Offset)
 		}
-	} else if filter.Offset > 0 {
-		// If only offset is specified, use a large limit
-		qb.Limit(1000000).Offset(filter.Offset)
+		qb.OrderBy("id", "desc")
+		needReverse = true
+	} else {
+		if filter.Offset > 0 {
+			qb.Limit(1000000).Offset(filter.Offset)
+		}
+		qb.OrderBy("id", "asc")
 	}
 
-	// Order by created_at first, then by sequence within the same request
-	qb.OrderBy("created_at", "asc").OrderBy("sequence", "asc")
-
 	rows, err := qb.Get()
 	if err != nil {
 		return nil, err
@@ -173,6 +177,12 @@ func (store *Xun) GetMessages(chatID string, filter types.MessageFilter) ([]*typ
 		messages = append(messages, msg)
 	}
 
+	if needReverse {
+		for i, j := 0, len(messages)-1; i < j; i, j = i+1, j-1 {
+			messages[i], messages[j] = messages[j], messages[i]
+		}
+	}
+
 	return messages, nil
 }