Background

Sparked by: https://x.com/steipete/status/2015246890325946647

Current State

The web UI chat interface is built with Lit Web Components (ui/src/ui/):

• views/chat.ts - Main chat view (~380 lines)
• chat/message-normalizer.ts - Message format normalization
• chat/grouped-render.ts - Slack-style message grouping
• chat/tool-cards.ts - Tool call card rendering
• controllers/chat.ts - Gateway communication

Proposal

Migrate the chat interface to React + assistant-ui for:

• Better maintained component library
• Built-in streaming, markdown, code highlighting
• Composable primitives (shadcn/ui style)
• Active community and updates

Scope

• Only the chat interface - not the entire UI
• Use assistant-ui default styling
• Preserve existing features:
  • Tool card sidebar (long output display)
  • Message queue
  • Thinking/reasoning display
  • Streaming with abort

Technical Approach

1. Use ExternalStoreRuntime to integrate with existing GatewayBrowserClient
2. Create message format adapter (NormalizedMessage → assistant-ui format)
3. Coexist with Lit app during migration (React mounts in chat tab only)

References

• assistant-ui docs: https://www.assistant-ui.com/docs
• ExternalStoreRuntime: https://www.assistant-ui.com/docs/runtimes/custom/external-store