State and streaming

UIMessage[]
   ↓ uiMessagesToMessages
ClientStreamRequest
   ↓ ClientTransport
ClientStreamFrame / ClientStreamEvent
   ↓ applyClientStreamEvent
UIMessage[] + status + usage + interactions

events retains protocol events for the current request. messages is reduced UI state; text and completion are derived convenience values.

Starting a new request aborts the previous transport. stop() aborts the active controller, and unmount does the same. HTTP cancellation may not undo provider or tool work already in progress, so server operations still need cancellation and idempotency rules.

Resume

const chat = useChat({
  transport,
  resume: {
    key: 'support-chat',
    storage: 'sessionStorage',
    auto: true,
  },
})

The hook stores v3 state containing streamId, the latest event ID, messages, interactions, and the last typed request. A matching resumeClientStreamResponse() route replays later records. Terminal streams clear resume state.

Interaction phases

When an agent suspends, the hook enters waiting and adds the request to chat.interactions.pending. Calling respondToInteraction() sends a discriminated interaction_response request. The application server resolves that ID to its trusted continuation and begins a linked stream phase; the continuation itself never belongs in browser state.

Smoothing hooks only buffer displayed values. They do not change source messages, events, or persistence.