Spec clarification: when does body.state reflect the latest STATE_SNAPSHOT, and is forwardedProps the recommended per-turn channel?

[sunholo-voight-kampff]

Question

The AG-UI spec describes shared state via STATE_SNAPSHOT / STATE_DELTA events that the client mirrors into agent.state. We've found in practice that the body.state field arriving on turn N mirrors the STATE_SNAPSHOT emitted at the end of turn N-1, not anything emitted during turn N itself.

This makes state useful for cross-turn persistence but unsuitable as a channel for per-turn ephemeral signals (e.g. "the user attached these documents to this message", "here's the current state of the UI surface as the user just interacted with it").

We've routed around this by using forwardedProps as a sibling channel for turn-scoped data:

• forwardedProps.document_ids — files the user attached to this turn
• forwardedProps.a2ui_surface_state — current snapshot of mounted A2UI surfaces
• forwardedProps.resumed_session — resume signal

Backend then reads forwardedProps first and falls back to body.state for genuine cross-turn data.

What we'd like to clarify

1. Is the "one turn behind" semantics of body.state intentional and spec-blessed, or an artefact of common implementations (ag_ui_adk etc.)?
2. Is forwardedProps the recommended channel for per-turn ephemeral signals, or is there a different recommended pattern?
3. Would it make sense to document this distinction explicitly in docs.ag-ui.com/concepts/state so newcomers don't rediscover it via the bug-trail?
4. Is there appetite for a future protocol-level addition of a turn-scoped state channel (alongside the snapshot+delta cross-turn one)?

Related discussions / issues

• pydantic-ai #2906 — "force STATE_SNAPSHOT at end of run"
• agno-agi/agno #4425 — state events feature request
• microsoft/agent-framework discussion #2966 — state management patterns

Happy to contribute a docs PR if there's consensus on the answer.

cc @MarkEdmondson1234