a2a-market-websocket-realtime

# 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` ## Minimum Contracts (MVP P0) 1. `subscribe(channel, cursor)` validates permission and registers stream. 2. `publish_event(channel, event)` fans out to online subscribers. 3. `resume(channel, cursor)` replays missed events within retention window. 4. `heartbeat(connection_id)` updates liveness and cleanup scheduling. ## Required Event Coverage - `INTENT_CREATED` - `QUOTE_RECEIVED` - `NEGOTIATION_STARTED` - `ORDER_CREATED` - `PAYMENT_SUCCEEDED` ## Guardrails - Keep payloads versioned and backward compatible. - Limit per-connection queue to prevent memory blowups. - Drop unauthorized subscription attempts with structured error codes. ## Implementation Backlog - Add presence channels and typing/status hints for negotiation UI. - Add regional relay nodes for cross-region latency reduction. ## Runtime Implementation - Status: implemented in local runtime package. - Primary code paths: - `runtime/src/interfaces/ws/event-bus.js` - Validation: covered by `runtime/tests` and `npm test` in `runtime/`.