Enum Event 

#[non_exhaustive]
pub enum Event {
    Init {
        session_id: String,
        harness: String,
        api_schema: String,
        model: String,
        cwd: String,
        max_turns: Option<u32>,
        preamble: Vec<Message>,
        tools: Vec<Value>,
    },
    Message {
        message: Message,
    },
    MessageDelta {
        text: String,
    },
    MessageDeltaReset {
        reason: String,
    },
    Result {
        report: Report,
    },
    Error {
        message: String,
    },
    Approval {
        tool_use_id: String,
        tool_name: String,
        decision: String,
        wait_ms: u64,
    },
}

One event in the stream-json trajectory (one JSON object per line).

The stream is a self-sufficient, replayable source of the whole run: Init carries the base prompt + tool specs + model, and each Event::Message carries a full turn — so reconstruct_conversation rebuilds the entire history with nothing else. (Claude Code’s stream omits system/tools, forcing a proxy capture to recover them; Init closes that gap.) #[non_exhaustive] so events can be added (e.g. per-turn markers) without a breaking change.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Init

Emitted once at the start — everything needed to reconstruct context.

Fields

session_id: String

The session identifier.

harness: String

The harness pack in use (e.g. grok).

api_schema: String

The wire schema in use (e.g. anthropic) — the provider’s api_schema().

model: String

The model id.

cwd: String

The working directory.

max_turns: Option<u32>

The max-turns ceiling; absent = unlimited (the default — ADR-0005 amendment 2026-07-18).

preamble: Vec<Message>

The base System + Developer messages (prompt + capabilities).

tools: Vec<Value>

The tool specs offered to the model (name + JSON schema), as JSON values.

Message

A full message appended to the history (the trace): role + content blocks.

Fields

message: Message

The appended message.

MessageDelta

An incremental assistant-text fragment during a streaming turn (ADR-0021). Display-only: the whole Message is still appended at turn end, so deltas are not part of the reconstructed history (the trace stays whole-message — Q1). Emitted only when the engine runs in streaming mode; consumers that want a whole-message trace drop this variant.

Fields

text: String

One assistant-text fragment — append to the live buffer.

MessageDeltaReset

The in-flight streamed message was abandoned, and every Event::MessageDelta emitted since the last Event::Message is void.

The engine resamples a turn after a retryable provider error, re-running the same request — so a stream that failed part-way is followed by a second stream of the same reply from the start. Without this marker a consumer that buffers deltas shows the reply twice. Discard the buffer and start it over; the turn itself is not lost.

Consumers that ignore Event::MessageDelta (the whole-message trace) can ignore this too — the eventual Event::Message is unaffected.

A caveat this event cannot fix: text a UI has already committed to the terminal’s scrollback cannot be withdrawn, so a long partial reply may still be visible above the re-streamed one.

Fields

reason: String

Why the stream was abandoned — the provider error, for the trace.

Result

The terminal event: the final report (identical to --output-format json).

Fields

report: Report

The run’s report envelope.

Error

A non-terminal error note (e.g. a retry); terminal errors ride in Event::Result.

Fields

message: String

A human-readable message.

Approval

An approver resolution at the dispatch gate (ADR-0017) — grok’s journal shape (PermissionResolved). Emitted for every consulted call, allowed or denied, so interactive traces are complete; wait_ms (human decision latency) is unrecoverable from any other artifact.

Fields

tool_use_id: String

The tool_use id the decision applies to.

tool_name: String

The client-facing tool name.

decision: String

The resolution: "allow" or "deny".

wait_ms: u64

Milliseconds spent awaiting the approver (human decision latency).

Trait Implementations

impl Clone for Event

fn clone(&self) -> Event

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Event

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Event

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl PartialEq for Event

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

Equality operator ==.

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

Inequality operator !=.

impl Serialize for Event

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 Event