fix

server/internal/websocket/websocket.go

@@ -518,8 +518,11 @@ func WebSocketHandler(db *gorm.DB) func(*websocket.Conn) {
 						ImageBuffer json.RawMessage `json:"imageBuffer"`
 					} `json:"data"`
 				}
-				if err := json.Unmarshal(msgBytes, &frameMsg); err == nil {
+				if err := json.Unmarshal(msgBytes, &frameMsg); err == nil && len(frameMsg.Data.ImageBuffer) > 0 {
-					Hub.RelayFrameRaw(client.StudentID, eventMsg.Event, frameMsg.Data.ImageBuffer)
+					// Copy slice to avoid memory race / corruption since WebSocket read buffer gets recycled
+					bufCopy := make([]byte, len(frameMsg.Data.ImageBuffer))
+					copy(bufCopy, frameMsg.Data.ImageBuffer)
+					Hub.RelayFrameRaw(client.StudentID, eventMsg.Event, json.RawMessage(bufCopy))
 				}
 				continue
 			}