Struct SessionState 

pub struct SessionState {
    pub id: String,
    pub created_at: String,
    pub title: Option<String>,
    pub runtime: Arc<Mutex<AgentRuntime>>,
    pub plan_approval_gate: Arc<PlanApprovalGate>,
    pub interrupt_token: Arc<Mutex<Option<CancellationToken>>>,
    pub non_system_message_count: Arc<AtomicUsize>,
    pub last_active_ms: Arc<AtomicU64>,
    pub prompt_tokens: Arc<AtomicU64>,
    pub completion_tokens: Arc<AtomicU64>,
}

Internal session state (not directly serialized to clients).

The AgentRuntime owns the transcript; this struct adds HTTP-layer metadata (id, created_at) and the broadcast channel for SSE clients.

Fields

id: String

created_at: String

title: Option<String>

Optional human-readable title, settable via PATCH /sessions/:id.

runtime: Arc<Mutex<AgentRuntime>>

Runtime is wrapped in a per-session Mutex so concurrent HTTP requests for the same session are serialized without blocking the global lock.

plan_approval_gate: Arc<PlanApprovalGate>

Shared gate for plan-mode approval. Stored here so HTTP handlers can approve/reject without taking the runtime Mutex (which may be held by a running agent turn).

interrupt_token: Arc<Mutex<Option<CancellationToken>>>

Goal-170: cancellation token for the currently running agent turn. POST /sessions/:id/interrupt cancels this token, which causes the kernel to exit with FinishReason::Cancelled at the next step boundary. Replaced with a fresh token at the start of every turn.

non_system_message_count: Arc<AtomicUsize>

Approximate non-system message count, updated atomically as messages are appended. Allows list_sessions to read the count without taking the runtime Mutex (which may be held by a running agent turn).

last_active_ms: Arc<AtomicU64>

Milliseconds since [SESSION_EPOCH] when this session was last active. Updated atomically on every message. Used by the session reaper.

prompt_tokens: Arc<AtomicU64>

Cumulative prompt tokens consumed in this session (all turns combined).

completion_tokens: Arc<AtomicU64>

Cumulative completion tokens generated in this session.