Enum FlowExecutionEvent 

pub enum FlowExecutionEvent {
    FlowStart {
        flow_name: String,
        backend: String,
        timestamp_ms: u64,
    },
    StepStart {
        step_name: String,
        step_index: usize,
        step_type: String,
        timestamp_ms: u64,
    },
    StepToken {
        step_name: String,
        content: String,
        token_index: u64,
        timestamp_ms: u64,
    },
    StepComplete {
        step_name: String,
        step_index: usize,
        success: bool,
        full_output: String,
        tokens_input: u64,
        tokens_output: u64,
        timestamp_ms: u64,
    },
    ToolCall {
        step_name: String,
        tool_name: String,
        content: String,
        timestamp_ms: u64,
    },
    FlowComplete {
        flow_name: String,
        backend: String,
        success: bool,
        steps_executed: usize,
        tokens_input: u64,
        tokens_output: u64,
        latency_ms: u64,
        timestamp_ms: u64,
    },
    FlowError {
        flow_name: String,
        error: String,
        timestamp_ms: u64,
    },
}

One observable moment in a flow’s execution. Closed catalog per D2.

Field naming + JSON serde-rename match the Python mirror (axon/runtime/flow_execution_event.py) byte-for-byte. The drift gate at tests/fixtures/fase33_flow_execution_event/corpus.json asserts both stacks produce byte-identical JSON for each variant.

Variants

FlowStart

Emitted exactly once at the very start of execution.

Fields

flow_name: String

backend: String

timestamp_ms: u64

StepStart

Emitted exactly once per step at its start boundary.

Fields

step_name: String

step_index: usize

step_type: String

timestamp_ms: u64

StepToken

Emitted per token / chunk produced by the step’s underlying backend. The granularity matches the backend’s chunk size (Anthropic SSE delta, OpenAI streaming chunk, etc.). For non-streaming backends, fires once per step with the full output (post-StepComplete in practice; the catalog allows it to fire either before or after but the convention is during execution).

Fields

step_name: String

content: String

token_index: u64

Monotonic counter, per-flow. Restarts at 1 for each new FlowStart. Adopter clients use this to correlate Last-Event-ID resumes (W3C SSE spec).

timestamp_ms: u64

StepComplete

Emitted exactly once per step at its end boundary.

Fields

step_name: String

step_index: usize

success: bool

full_output: String

tokens_input: u64

tokens_output: u64

timestamp_ms: u64

ToolCall

§Fase 33.y.k — Tool invocation chunk. Emitted by per-step handlers when the upstream backend’s chunk stream signals FinishReason::ToolUse (provider invoked a tool mid-stream). Closed-catalog event variant; D4 byte-compat preserves adopter parsers — flows without declared apply: <tool> never emit this event.

content carries the tool-call’s structured payload as a canonical wire-stable string (provider-specific shape today; future Fase 33.y.k.2 standardizes per-provider extraction into a unified tool_call_id + arguments schema).

Fields

step_name: String

tool_name: String

content: String

timestamp_ms: u64

FlowComplete

Terminator — success path. Receiver MUST close the stream.

Fields

flow_name: String

backend: String

success: bool

steps_executed: usize

tokens_input: u64

tokens_output: u64

latency_ms: u64

timestamp_ms: u64

FlowError

Terminator — failure path. Receiver MUST close the stream.

Fields

flow_name: String

error: String

timestamp_ms: u64

Implementations

impl FlowExecutionEvent

pub fn is_terminator(&self) -> bool

Closed predicate: is this the terminator of the stream? After emitting a terminator, the producer MUST drop the sender so the receiver’s recv() returns None.

pub fn is_step_scoped(&self) -> bool

Closed predicate: is this event step-scoped (carries step_name)?

pub fn kind(&self) -> &'static str

String kind for diagnostic / log lines. Matches the JSON kind discriminator field (snake_case per serde-rename).

Trait Implementations

impl Clone for FlowExecutionEvent

fn clone(&self) -> FlowExecutionEvent

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for FlowExecutionEvent

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for FlowExecutionEvent

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl PartialEq for FlowExecutionEvent

fn eq(&self, other: &FlowExecutionEvent) -> 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 FlowExecutionEvent

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 FlowExecutionEvent