a2a-Market WebSocket Realtime

Set up realtime delivery skeleton for buyer and operator clients.

Current status: publishable framework with stable event contracts, not full scale tuning.

Scope

• Define channel naming and auth guard for buyer, node, and admin roles.
• Push canonical domain events with predictable payload shape.
• Manage reconnect semantics and last-event cursor replay.

Suggested Project Layout

• app/interfaces/ws/socket_gateway.py
• app/application/services/realtime_service.py
• app/infrastructure/ws/connection_registry.py
• app/infrastructure/cache/replay_cursor_store.py