Improve message ID tracking in streaming chat processing

- Updated ScanTokens method to preserve and reuse existing message IDs
- Modified streaming chat to track and pass current message ID during token scanning
- Ensured consistent message ID generation when not explicitly provided

neo/assistant/api.go

@@ -283,6 +283,7 @@ func (ast *Assistant) streamChat(
 
 	errorRaw := ""
 	isFirst := true
+	currentMessageID := ""
 	err := ast.Chat(c.Request.Context(), messages, options, func(data []byte) int {
 		select {
 		case <-clientBreak:
@@ -321,7 +322,8 @@ func (ast *Assistant) streamChat(
 				msg.AppendTo(contents) // Append content and send message
 
 				// Scan the tokens
-				contents.ScanTokens(func(token string, id string, begin bool, text string, tails string) {
+				contents.ScanTokens(currentMessageID, func(token string, id string, begin bool, text string, tails string) {
+					currentMessageID = id
 					msg.ID = id
 					msg.Type = token
 					msg.Text = ""                                    // clear the text

neo/message/contents.go

@@ -49,7 +49,7 @@ func NewContents() *Contents {
 }
 
 // ScanTokens scan the tokens
-func (c *Contents) ScanTokens(cb func(token string, id string, begin bool, text string, tails string)) {
+func (c *Contents) ScanTokens(currentID string, cb func(token string, id string, begin bool, text string, tails string)) {
 
 	text := strings.TrimSpace(c.Text())
 
@@ -79,7 +79,10 @@ func (c *Contents) ScanTokens(cb func(token string, id string, begin bool, text
 	for name, token := range tokens {
 		if index := strings.Index(text, token[0]); index >= 0 {
 			c.token = name
-			c.id = uuid.New().String()
+			c.id = currentID
+			if c.id == "" {
+				c.id = uuid.New().String()
+			}
 			cb(name, c.id, true, text, "") // call the callback
 		}
 	}