Context

Implement real-time WebSocket streaming using Litestar's built-in channels plugin for pub/sub broadcasting. The channels plugin handles connection management, per-channel subscriptions, backpressure, and subscriber backlog out of the box.

Streamed events include:

• Agent messages (inter-agent communication)
• Task status changes (created, assigned, in progress, completed, failed)
• Budget and cost update events (spending events, budget warnings)
• System events (agent hired/fired, errors)

Acceptance Criteria

• Litestar channels plugin configured with channel definitions
• Channels for each event type: tasks, agents, budget, messages, system
• WebSocket endpoint at /api/v1/ws with channel subscription support
• Clients can subscribe to specific channels (filter by event type, agent, project)
• JSON message format with event type, timestamp, and payload
• Integration with message bus from M4 for event sourcing
• Backpressure handling configured (backoff or eviction strategy)
• Connection heartbeat/ping-pong for keep-alive
• Unit tests for channel event serialization and subscription

Dependencies

• Set up Litestar application with REST API skeleton #31 — Litestar skeleton must be set up
• Evaluate and implement message bus (asyncio queues vs external broker) #8 — Message bus (closed, M4)

Design Spec Reference

• §13.1 — API architecture (real-time requirements)