# `Feel.Worker.Preflight`
[🔗](https://github.com/FeeJai/BDM/blob/feel-v0.1.0/apps/feel/lib/feel/worker/preflight.ex#L1)

The budget of the preflight: the step that runs in the caller, before a worker exists, and decides what the job closure
copied into the worker holds (the internal `run_prepared` entry point of `Feel.Worker`). Internal: not a supported API.

A worker is another process, so what it runs is copied into its heap and counted against `:max_input_bytes`. A selector
(`Dmn.Execution.prepare/6` for DMN, the binding selection of `Feel.run/3` for FEEL) picks the part of the model and the
bindings a call needs, and this module bounds that work, because no worker's deadline or heap policy protects it yet:

  * `project/2` gives the selector a state with a step budget of at most 100,000 (less for a small memory or input policy)
    and the deadline. The deadline is read when the selection starts and then every 64 steps (`step/1`; a step is constant
    work, and the transfer walk checks every 256).
  * Only library-owned, shallow work runs here, never host code: no extension, callback or resolver is called.
  * What it cannot decide, or cannot afford (`fallback/0`: a key that is too long, a spent budget, uncertain metadata), makes
    it send the original, complete argument instead, which faces the same transfer check. Expiry is a
    `{:error, :timeout}` of the whole operation, not a fresh deadline.

Selection is an optimization of what is copied and never validation: the worker validates again. See the
[preflight](architecture.md#the-preflight) in the architecture.

# `t`

```elixir
@type t() :: %{deadline: integer(), left: non_neg_integer()}
```

# `bindings`

```elixir
@spec bindings(map(), MapSet.t() | nil, t()) :: map()
```

# `fallback`

```elixir
@spec fallback() :: no_return()
```

# `project`

```elixir
@spec project(map(), (t() -> value)) :: {:ok, value} | :fallback | {:error, :timeout}
when value: term()
```

# `step`

```elixir
@spec step(t()) :: t()
```

---

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