# `Impact.Runtime`

One-call runtime configuration. Designed to be invoked from `config/runtime.exs`
in a Phoenix/Mix application — BEFORE any application starts — so the
`:opentelemetry` and `:opentelemetry_exporter` supervision trees boot with
Impact's OTLP endpoint and auth header already wired in.

## Why this exists

The Erlang OpenTelemetry exporter reads its endpoint and headers from
Application env *at supervision-tree startup*. Calling `Impact.init/1` from
inside a running application is too late — the exporter has already booted
with empty config and will not pick up new values without being restarted.

`config/runtime.exs` is the standard Elixir hook that runs **after compile
but before any application starts**. It is the correct seam for this kind
of dependency-time configuration.

## Usage in a Phoenix / Mix app

    # config/runtime.exs
    import Config
    Impact.Runtime.configure!()

That single line is the full integration. `:impact` reads
`IMPACT_API_KEY` (required) and `IMPACT_BASE_URL` (optional — derived from
the key's region if absent) at boot. No `Impact.init/1` call is required;
the `:impact` OTP application picks the config up on its own start.

## Usage in a one-off script

Mix scripts (`mix run path.exs`) do **not** evaluate `config/runtime.exs`,
so scripts must call `Impact.Runtime.configure!/1` at the top **with
`--no-start`**, then start apps explicitly:

    Impact.Runtime.configure!(api_key: "impact_dev_...")
    {:ok, _} = Application.ensure_all_started(:impact)

## Overrides

All values can be passed as keyword options, taking precedence over env vars:

    Impact.Runtime.configure!(
      api_key: "impact_dev_...",
      endpoint: "https://api.dev.impact.ai",
      service_name: "my_app",
      resource_attributes: %{deployment: %{environment: "staging"}}
    )

# `configure!`

```elixir
@spec configure!(keyword()) :: :ok
```

---

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