轻量级声明式语法层，在 Orchid.Step / OrchidSymbiont.Step 之上提供简易 API，并产出 __node_spec__/0 供 topology 集成。

Pure step

defmodule MyApp.Steps.Upcase do
  use Oi.Step, name: :upcase

  manifest(
    inputs: [:text],
    outputs: [result: :string]
  )

  routine text, opts do
    report(opts, 100, "Reached!")
    text |> String.upcase() |> ok()
  end
end

Symbiont step

defmodule MyApp.Steps.Predict do
  use Oi.Step, name: :predict, symbiont?: true

  manifest(
    inputs: [:features],
    outputs: [prediction: :tensor],
    models: [:encoder, :predictor],
    heavy?: true
  )

  routine features, models, opts do
    {:ok, {enc}} = OrchidSymbiont.call(models.encoder, {:infer, features})
    ok(enc)
  end
end

ok / err — Rust 风格结果构造器

routine text, opts do
  case validate(text) do
    {:ok, v}    -> ok(v)
    {:error, e} -> err(e)
  end
end

• 单输出：ok(value) → {:ok, %Orchid.Param{}}
• 多输出：ok({a, b}) / ok([a, b]) → {:ok, [%Param{}, %Param{}]}