[direct-messaging] Implement real-time message reception (Backend)

[TheFourthKaramazov]

User Story (Backend)

As a user, I want the backend to handle and forward received direct messages in real time so that they appear instantly for the recipient.

Description

The backend should manage WebSocket connections and route incoming messages to the correct recipient in real time.

Tasks (Backend - FastAPI, WebSockets, SQLite/PostgreSQL)

• Maintain an active WebSocket connection for authenticated users.
• Receive direct messages and forward them to the intended recipient in real time.
• Ensure that offline users have their messages stored for later retrieval.
• Handle potential connection issues and retries.

Acceptance Criteria

• Messages are forwarded instantly to the correct recipient if they are online.
• Messages for offline users are stored and delivered when they reconnect.
• WebSocket connections remain stable during active use.

Priority

High

Labels

• backend
• direct-messaging
• real-time
• core-feature