Struct Session 

pub struct Session {
    pub conversation: ConversationHistory,
    pub model_id: String,
    pub reasoning: ReasoningLevel,
    pub safety_mode: SafetyMode,
    pub cumulative_tokens: usize,
    pub last_token_usage: Option<TokenUsageTotals>,
    pub cumulative_token_usage: TokenUsageTotals,
    pub context_usage: Option<ContextUsageSnapshot>,
    pub is_subagent: bool,
    pub agent_preamble: Option<String>,
}

Persistent conversational state that survives across turns.

“Session” here means the user-visible chat session, not the tokio runtime or the TCP connection to the provider. One chat = one Session = one on-disk ConversationHistory file.

Fields

conversation: ConversationHistory

model_id: String

reasoning: ReasoningLevel

safety_mode: SafetyMode

Live safety mode for this session. Initialized from config.safety.mode, then mutated in-session by Shift+Tab / /safety (session-scoped — never written back to the config file). The reducer threads this into Cmd::ExecuteTool so the policy gate enforces the current mode, not the startup snapshot.

cumulative_tokens: usize

Running total of tokens consumed across every API request in this session. Kept for CLI JSON compatibility; the richer prompt/completion breakdown lives in cumulative_token_usage.

last_token_usage: Option<TokenUsageTotals>

Token usage for the most recent completed provider request. None means the provider did not report usage for that turn.

cumulative_token_usage: TokenUsageTotals

Prompt/completion/total API usage accumulated for this session.

context_usage: Option<ContextUsageSnapshot>

Latest model-visible context snapshot. This may be an estimate while a request is in flight and is replaced by provider-reported usage when available.

is_subagent: bool

True when this session IS a subagent (a child reducer driven by SubagentTool). system_prompt_for_state appends the subagent contract (final message = the report returned to the parent) when set. Never true for a user-facing session.

agent_preamble: Option<String>

Agent-type system-prompt block (e.g. the Explore type’s “read-only reconnaissance” charter), appended after the subagent contract. Only ever Some on subagent sessions.

Implementations

impl Session

pub fn messages(&self) -> &[ChatMessage]

The committed message log. All messages visible in the chat widget live here; partial in-flight content lives in TurnState::Generating.

pub fn append(&mut self, msg: ChatMessage, now: DateTime<Local>)

Append a committed assistant/user/tool message. Mutation happens through here so the reducer has one chokepoint to update the conversation’s updated_at and derived title.

now is the reducer’s injected clock (state.now). It stamps both the message’s commit timestamp and updated_at — the wall-clock stamp ChatMessage::new put on the message at construction is deliberately overwritten with the deterministic one, so update() is a pure function and --replay recommits identical messages.

Trait Implementations

impl Clone for Session

fn clone(&self) -> Session

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Session

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.