Struct SessionHeader 

pub struct SessionHeader {
    pub session_id: Option<SessionId>,
    pub model: Option<CurrentModel>,
    pub effort: EffortLevel,
    pub permission_mode: Option<PermissionMode>,
    pub context: ContextUsage,
    pub available_models: Vec<AvailableModel>,
    pub turn_in_flight: bool,
}

What a session header states about the session.

Fields

session_id: Option<SessionId>

The occupant’s id, as the CLI named it, or None when there is no occupant to name: a seat nothing has started, one whose CLI has not answered yet, and one whose id was dropped after a background sign-in or connection failure all read the same.

Carried here rather than read off the conversation’s frames, because a client attaching to a running seat hears no Connected - a subscription carries no backlog - and a frame’s id is the turn’s fact rather than the seat’s. The worker registry carries the id for a live dynamic worker, and nothing carries it for any other seat.

model: Option<CurrentModel>

The model the CLI resolved for this session, from its connect and from every later frame that names a different one.

effort: EffortLevel

The effort the session runs at: the hook-observed level when the session has reported one, else the level its launch stamped, else forge’s default. Always a value rather than an Option, because a session that has not used a tool yet still runs at some level and a header that showed nothing there would be wrong.

permission_mode: Option<PermissionMode>

The permission mode the session runs in: the hook-observed mode when one has fired, else the level its launch stamped, which forge always writes from its own effective default. None only when the launch pinned nothing and no hook has reported, which is a session nothing has started.

context: ContextUsage

How full the context window is, from the bridge’s last answer.

available_models: Vec<AvailableModel>

The model catalogue the session’s connect resolved against, which a picker draws its rows from. Empty for a session nothing has started.

turn_in_flight: bool

Whether a turn is in flight, from the core’s own OR of the stamped signal and the wire-lagged one: the two disagree in the window between a prompt being routed and its echo arriving, so a read of either alone is wrong for one of them.