Struct Checkpoint 

pub struct Checkpoint {
    pub id: String,
    pub system_prompt: String,
    pub provider: String,
    pub model_id: String,
    pub messages: Vec<LlmMessage>,
    pub custom_messages: Vec<Value>,
    pub turn_count: usize,
    pub usage: Usage,
    pub cost: Cost,
    pub created_at: u64,
    pub metadata: HashMap<String, Value>,
    pub state: Option<Value>,
    /* private fields */
}

A serializable snapshot of agent conversation state.

Captures everything needed to restore an agent to a previous point: messages, system prompt, model info, turn count, accumulated usage/cost, and arbitrary metadata.

Fields

id: String

Unique identifier for this checkpoint.

system_prompt: String

System prompt at the time of the checkpoint.

provider: String

Model provider name.

model_id: String

Model identifier.

messages: Vec<LlmMessage>

Conversation messages (LLM messages only).

custom_messages: Vec<Value>

Serialized custom messages (envelopes with type and data fields).

turn_count: usize

Number of completed turns at the time of checkpointing.

usage: Usage

Accumulated token usage.

cost: Cost

Accumulated cost.

created_at: u64

Unix timestamp when the checkpoint was created.

metadata: HashMap<String, Value>

Arbitrary metadata for application-specific use.

state: Option<Value>

Serialized session state snapshot (SessionState.data).

Implementations

impl Checkpoint

pub fn new( id: impl Into<String>, system_prompt: impl Into<String>, provider: impl Into<String>, model_id: impl Into<String>, messages: &[AgentMessage], ) -> Self

Create a new checkpoint from the current agent state.

Serializes CustomMessage variants that support serialization (i.e. type_name() and to_json() return Some). Custom messages that cannot be serialized are skipped with a warning.

Use with_turn_count(), with_usage(), and with_cost() to set additional fields.

pub fn with_state(self, state: Value) -> Self

Set the session state snapshot.

pub const fn with_turn_count(self, turn_count: usize) -> Self

Set the turn count.

pub fn with_usage(self, usage: Usage) -> Self

Set the accumulated usage.

pub fn with_cost(self, cost: Cost) -> Self

Set the accumulated cost.

pub fn with_metadata(self, key: impl Into<String>, value: Value) -> Self

Add metadata to this checkpoint.

pub fn restore_messages( &self, registry: Option<&CustomMessageRegistry>, ) -> Vec<AgentMessage>

Restore all messages as AgentMessage values, preserving their original interleaved order.

If registry is None, custom messages are silently skipped. Deserialization failures are logged as warnings but do not cause errors.

For checkpoints created before ordering support, falls back to legacy behavior (LLM messages first, then custom messages appended).

Trait Implementations

impl Clone for Checkpoint

fn clone(&self) -> Checkpoint

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Checkpoint

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Checkpoint

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for Checkpoint

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.