Enum AgentMessage 

pub enum AgentMessage {
    System {
        content: String,
        timestamp: Option<u64>,
    },
    User {
        content: UserContent,
        timestamp: Option<u64>,
    },
    Assistant {
        content: AssistantContent,
        stop_reason: StopReason,
        error_message: Option<String>,
        timestamp: Option<u64>,
        usage: Option<Usage>,
    },
    ToolResult {
        tool_call_id: String,
        tool_name: String,
        content: ToolResultContent,
        is_error: bool,
        narration: Option<String>,
        details: Option<Value>,
        timestamp: Option<u64>,
    },
    Custom {
        kind: String,
        payload: Value,
        timestamp: Option<u64>,
    },
}

One message in the conversation transcript.

Discriminated by role. Each variant carries its own payload shape; the loop pattern-matches, never field-walks.

Variants

System

System prompt. Typically only one, at the head of the transcript.

Fields

content: String

timestamp: Option<u64>

User

User input. May be a single text block or rich blocks (text + images).

Fields

content: UserContent

timestamp: Option<u64>

Assistant

Model output. Carries text, thinking blocks, and tool calls.

Fields

content: AssistantContent

stop_reason: StopReason

error_message: Option<String>

timestamp: Option<u64>

usage: Option<Usage>

Provider-reported token accounting for the call that produced this message. Populated by streaming transports that request stream_options.include_usage; consumed by cost/billing observers (e.g. eval matrix). None when the transport didn’t surface usage data.

ToolResult

Output of a tool call. Always paired with a prior assistant message that contains the corresponding ToolCall block.

Fields

tool_call_id: String

tool_name: String

content: ToolResultContent

is_error: bool

narration: Option<String>

Tool-side prose summary — the row-caption sentence the UI renders (“Ran ls -la.”, “Wrote index.html (4 KB).”, “Searched: rust async — 8 results.”). The loop fills this from ToolResult::narration when the typed result is appended to history; tools may set it deterministically from their own structured signals. Optional for backward-compatibility with persisted histories that pre-date this field.

working_memory_anchor and other history-aware plugins consume this in preference to walking the content blocks for a preview; the model’s first-line peek of a densified shell result is opaque metadata, while narration carries the actual prose every other surface already shows.

details: Option<Value>

Host-side structured payload carried from the tool’s ToolResult::details. Stripped from provider wire formats (the model sees content only) but preserved into history so host-side plugins — delivery gates, artifact dispatchers, UI projectors — can read structured fields without text-grepping. Typed producers (create_slides, create_website, publish) put canonical artifact metadata here (html_url, artifacts: [...], …). None when the tool returned no structured payload, or for messages deserialized from histories persisted before this field existed.

timestamp: Option<u64>

Custom

Escape hatch for app-specific message types (UI notifications, hidden runtime feedback, replay markers). The loop ignores these for tool dispatch but apps can route them through plugins or the event sink.

Fields

kind: String

payload: Value

timestamp: Option<u64>

Trait Implementations

impl Clone for AgentMessage

fn clone(&self) -> AgentMessage

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for AgentMessage

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for AgentMessage

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl PartialEq for AgentMessage

fn eq(&self, other: &AgentMessage) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for AgentMessage

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

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for AgentMessage