Implementation complete. PR created: https://github.com/RoM4iK/alpha/pull/45 ## Changes Summary ### Backend - Added `has_many_attached :files` to ChatMessage model - Added file validation constants (MAX_FILES=10, MAX_FILE_SIZE=500MB, blocked extensions) - Updated `to_nats_payload` to include attachments array with full metadata - Extended `Chats::SendMessageService` to handle file uploads with validation - Updated `ChatMessagesController` to accept multipart form data ### Frontend - Added attachment button (paperclip icon) to ChatRoom.jsx - Implemented drag-and-drop file upload with visual feedback - Added file preview area with remove capability - Updated Message component to display inline image thumbnails and file download links - Modified chat_service.js to use FormData when files are present ### Tests - All 22 tests pass - Added comprehensive coverage for file attachments in model and service specs