Agent Event Streaming via DO WebSocket Hibernation

[jrf0110]

Context

#338 introduced the MayorDO with a polling-based status panel. SSE through Workers is unreliable (buffering, connection drops at the edge). For real-time streaming of agent activity (tool calls, messages, completion events), we need WebSocket support.

Background

The kilo serve instances inside Cloudflare Containers already expose:

• GET /event — SSE stream of all session events (message.created, message.part.updated, session.completed, etc.)
• The container process manager (process-manager.ts) already subscribes to this stream internally

The kilo web app (packages/app/src) consumes these SSE events through a sophisticated coalescing/batching system in global-sdk.tsx. The data model is:

• Session → messages → parts (text, tool calls, reasoning, patches)
• Events are scoped by sessionID in the payload

Proposed Architecture

kilo serve /event (SSE, inside container)
  → Container process-manager (already subscribes)
  → Forward events to MayorDO/AgentDO via RPC
  → MayorDO stores session data in KV/SQL
  → MayorDO broadcasts to WebSocket clients via DO hibernation API
  → Frontend connects via WebSocket, renders kilo-style UI

Key decisions needed:

1. Session data storage: Store full session/message/part data in the DO? Or just forward events for real-time display and rely on the container for historical data?
2. UI approach: Port the kilo web app's SolidJS components to React? Or build simpler React components that consume the same event protocol?
3. Scope: Mayor only, or all agent types (polecat, refinery, witness)?

References

• kilo web app SSE consumer: packages/app/src/context/global-sdk.tsx
• kilo web app state model: packages/app/src/context/global-sync/types.ts
• kilo serve SSE event types: packages/sdk/js/src/v2/gen/types.gen.ts (Event union)
• Container SSE consumer: cloudflare-gastown/container/src/sse-consumer.ts
• Container process manager: cloudflare-gastown/container/src/process-manager.ts
• CF DO WebSocket hibernation: https://developers.cloudflare.com/durable-objects/api/websockets/

Part of #204