# `GenAgent.Event`
[🔗](https://github.com/genagent/gen_agent/blob/v0.2.0/lib/gen_agent/event.ex#L1)

A normalized event emitted by a backend during a prompt turn.

Backends translate their native event streams into `GenAgent.Event` values
so the state machine and user callbacks see a consistent shape regardless
of which LLM is on the other end.

## Event kinds

  * `:text` -- an assistant text chunk (delta). `data` carries `%{text: String.t()}`.
  * `:tool_use` -- the agent invoked a tool. `data` is backend-specific.
  * `:tool_result` -- a tool returned. `data` is backend-specific.
  * `:usage` -- token usage info. `data` typically carries
    `%{input_tokens: integer(), output_tokens: integer()}`.
  * `:result` -- terminal event for a successful turn. `data` carries at
    minimum `%{text: String.t()}` with the full assembled assistant text.
  * `:error` -- terminal event for a failed turn. `data` carries
    `%{reason: term()}`.

Exactly one terminal event (`:result` or `:error`) is emitted per turn.

# `kind`

```elixir
@type kind() :: :text | :tool_use | :tool_result | :usage | :result | :error
```

# `t`

```elixir
@type t() :: %GenAgent.Event{data: map(), kind: kind(), timestamp: integer()}
```

# `new`

```elixir
@spec new(kind(), map()) :: t()
```

Build an event of the given `kind` with `data`.

The timestamp is stamped from `System.monotonic_time/1` in milliseconds,
so event timestamps are suitable for computing durations within a single
turn but are not wall-clock values.

# `terminal?`

```elixir
@spec terminal?(t()) :: boolean()
```

True if the event is a terminal event (`:result` or `:error`).

Terminal events mark the end of a turn. The stream from
`c:GenAgent.Backend.prompt/2` should emit exactly one terminal event.

---

*Consult [api-reference.md](api-reference.md) for complete listing*