AG-UI React architecture
The AG-UI path has three boundaries: native protocol state, application policy, and React presentation. Keeping them separate prevents a visible protocol event from becoming an unintended command.
This architecture describes experimental, private source-build packages.
Native session
The private session owns the request and protocol reduction. Its snapshot includes native transcript, state, subagents, and root run evidence. Tool arguments can remain partial protocol strings.
useAgent can borrow this object directly because it only needs snapshot and subscription methods. It preserves the concrete native type; it does not translate the snapshot to core messages or invent execution states.
Application owner
The streaming fixture wraps that session to publish rows, busy state, submission permission, and an outcome. It projects root text with the native text projection and confirms terminal history against the owned turn.
The application also owns stop, replacement, disposal, and stale-result checks. A matching success outcome alone is insufficient if the transcript no longer represents the admitted question and prior conversation.
Different examples deliberately admit different evidence. The subagents example preserves explicit child attribution; the client-tools example owns supported execution. Root text selection must not silently mix child output into canonical history.
React view
TextTranscript displays supplied structural text rows. ToolObservation displays literal supplied name, arguments, and optional result text. Neither executes a tool, parses partial arguments, or decides whether a follow-up is safe.
ChatInput forwards explicit user actions to the application. Unmounting an observer releases its subscription; the application separately retires the native session.
The protocol is backend-neutral, but the fixture's private constructor is not a public React adapter API. Use the exact example contracts and event mapping when investigating how native evidence reaches the UI.