Conversations

A session's history is a tree of messages, persisted by the engine. The worker builds no chat backend. A client edits, regenerates, and branches by resubmitting its view of the conversation, which the engine reconciles into the tree.

The tree

Each message is a node with a parent. The head is the active leaf, and the path from head to root is the conversation the model sees. A decision request carries that active path as messages, and the whole tree as message_tree.

Submitting

A client sends input two ways.

The engine matches a submitted view against the tree by message id. Known ids at the front line up with existing nodes; the first new or id-less message begins a new branch, and new_from on the trigger marks its index.

Editing and branching

To edit, resubmit the view with an earlier message changed and given a new id or none. The engine forks a branch at the last matching node, records the changed message and everything after it, and moves the head to the tip. The original branch stays in the tree. Regenerating is the same move: resubmit without the last assistant reply, and a new one is recorded as a sibling.

Resubmitting a message under its existing id changes nothing, since reconciliation keys on id, not content.

A view that stops at an earlier node — or resends another branch's view — writes nothing but moves the head there (head.moved on the event stream); the next reply forks at that node, and in-flight work on the abandoned branch is voided. Submitting a recorded branch's view is how a client switches branches.

Example

An active path of u1 → a1 → u2. The client edits back to the first question:

{
    "type": "client.messages",
    "agent_id": "bot",
    "messages": [
        { "id": "u1", "role": "user", "content": "weather in NYC?" },
        { "role": "user", "content": "weather in LA instead" }
    ]
}

u1 matches; the id-less message forks a branch under it. The worker sees messages: [u1, e1] with new_from: 1, and the a1 → u2 branch is kept.

Next

• Agent state: state resolves along the active path.
• AG-UI: drives this from a browser chat UI.
• Protocol: messages, the tree, and client inputs.