Struct Message 

pub struct Message {
    pub id: MessageId,
    pub role: MessageRole,
    pub content: Vec<ContentPart>,
    pub phase: Option<ExecutionPhase>,
    pub thinking: Option<String>,
    pub thinking_signature: Option<String>,
    pub controls: Option<Controls>,
    pub metadata: Option<HashMap<String, Value>>,
    pub external_actor: Option<ExternalActor>,
    pub created_at: DateTime<Utc>,
}

A message in the conversation

Fields

id: MessageId

Unique message ID (format: message_{32-hex})

role: MessageRole

Message role

content: Vec<ContentPart>

Message content as array of content parts (text, images, tool calls, tool results)

phase: Option<ExecutionPhase>

Execution phase for this message.

Helps LLMs distinguish between intermediate working commentary and completed answers in multi-step tool-calling flows. Only set on agent (assistant) messages. Providers with native phase support (OpenAI GPT-5.x) send this value in the API request; others derive it from state but don’t send it to the provider.

thinking: Option<String>

Thinking content from extended thinking models (Anthropic Claude) This is the model’s chain-of-thought reasoning before producing the response. Must be included in subsequent API calls when thinking is enabled.

thinking_signature: Option<String>

Cryptographic signature for thinking content (Anthropic Claude) Required when sending thinking back in subsequent API calls.

controls: Option<Controls>

Runtime controls (model, reasoning, etc.)

metadata: Option<HashMap<String, Value>>

Message-level metadata

external_actor: Option<ExternalActor>

External actor identity (for messages from external channels like Slack)

created_at: DateTime<Utc>

Timestamp when the message was created

Implementations

impl Message

pub fn user(content: impl Into<String>) -> Self

Create a new user message

pub fn assistant(content: impl Into<String>) -> Self

Create a new assistant message

pub fn assistant_with_tools( content: impl Into<String>, tool_calls: Vec<ToolCall>, ) -> Self

Create a new assistant message with tool calls

Tool calls are stored as ContentPart::ToolCall in the content array alongside the text content. Empty text content is omitted to avoid LLM API errors (e.g., Anthropic requires non-empty text blocks).

pub fn system(content: impl Into<String>) -> Self

Create a new system message

pub fn tool_result( tool_call_id: impl Into<String>, result: Option<Value>, error: Option<String>, ) -> Self

Create a tool result message

pub fn tool_result_with_images( tool_call_id: impl Into<String>, result: Option<Value>, images: Vec<ToolResultImage>, ) -> Self

Create a tool result message with images.

Images are included as ContentPart::Image alongside the ToolResult part. When converted to LlmMessage, images become native image content blocks that the LLM can see visually (not just stringified base64).

pub fn with_phase(self, phase: ExecutionPhase) -> Self

Set the execution phase on this message and return self.

pub fn tool_call_id(&self) -> Option<&str>

Get the tool_call_id from a tool result message

Returns the tool_call_id from the first ToolResult content part, if any.

pub fn text(&self) -> Option<&str>

Get first text content from the message

pub fn tool_calls(&self) -> Vec<&ToolCallContentPart>

Get all tool calls from the message content

pub fn has_tool_calls(&self) -> bool

Check if this message has tool calls

pub fn tool_result_content(&self) -> Option<&ToolResultContentPart>

Get the first tool result from the message content

pub fn content_to_llm_string(&self) -> String

Convert content to LLM-compatible string representation

pub fn to_openai_format(&self) -> Value

Convert message to OpenAI-compatible format

Transforms internal message format to OpenAI API format:

• agent role → assistant
• tool_result role → tool (with tool_call_id at message level)
• Tool calls formatted as {id, type: "function", function: {name, arguments}}

Used by observability backends (e.g., Braintrust) that expect OpenAI format.

Trait Implementations

impl Clone for Message

fn clone(&self) -> Message

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Message

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Message

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl From<&Message> for LlmMessage

fn from(msg: &Message) -> Self

Convert a Message to LlmMessage (text-only, images become placeholders)

This conversion is suitable for messages without images or when image resolution is not available. For multimodal messages, use LlmMessage::from_message_with_images() instead.

impl Serialize for Message

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

where __S: Serializer,

Serialize this value into the given Serde serializer.