ReAct

The ReAct (Reason + Act) graph is the graph implementation shipped in this distribution. It runs a reasoning loop: receive input, call the model, the model may request tools, tools execute and return results, the loop repeats until the model produces a final response. Every step is checkpointed so the agent can survive crashes and resume from where it left off.

The graph is selected explicitly in the manifest with graph { type = "react" }. Once selected, ReAct defines the runtime contract for the agent: durable sessions and runs, persisted messages, a client-visible context object, a set of prompt variables, and the event stream that drives the HTTP surface.

Because this contract is specific to the graph, its reference lives here rather than in a shared location. A different graph would expose a different set of endpoints, prompt variables, and state.

Sessions and runs

A session is the durable container for a conversation. A run is one execution of the graph inside a session. The runtime persists both, so a client can return later and inspect history without having to replay the original request immediately. Messages are persisted separately from run state, so a client can read conversation history outside of an active run.

Runs can be started in attached mode, where the starting request streams events until the run finishes, or detached mode, where the server returns the run and session IDs and keeps executing the run in the background. Active runs can also be observed through a live reattach stream. Reattachment does not replay earlier events; persisted run and message history remain available through the read endpoints.

Because every step is checkpointed, a run can also be started from an earlier checkpoint instead of the session's latest state. Doing so creates a new run whose history descends from the chosen checkpoint, so the original run's history is left unchanged. List a session's checkpoints with the checkpoints endpoint to find one to start from.

Reference in this section

• HTTP reference: the native /v1 endpoints for sessions, messages, runs, and live run event streams.
• Prompt templates: the variables the ReAct graph injects into the system prompt.
• State: the run state structure, how tools update it, and what clients can see.

The AG-UI add-on translates the same underlying graph behavior into the AG-UI event schema. It is a protocol wrapper rather than part of the graph, so it is documented separately under AG-UI.