# `Mailglass.Tracking.ConfigValidator`
[🔗](https://github.com/szTheory/mailglass/blob/v1.0.0/lib/mailglass/tracking/config_validator.ex#L1)

Boot-time validator for TRACK-03 configuration (D-32).

When ANY loaded mailable module has `tracking: [opens: true]` or
`tracking: [clicks: true]` in its `@mailglass_opts`, the
`config :mailglass, :tracking, host:` key is REQUIRED. Boot fails
with `%Mailglass.ConfigError{type: :tracking_host_missing}` on
omission.

## Adopter usage (v0.1)

Call from your `Application.start/2` callback after
`Mailglass.Config.validate_at_boot!/0`:

    def start(_type, _args) do
      Mailglass.Config.validate_at_boot!()
      Mailglass.Tracking.ConfigValidator.validate_at_boot!()
      # ...
    end

v0.5 will auto-wire this into `Mailglass.Config.validate_at_boot!/0`.

## Detection algorithm

Walks `:code.all_loaded/0` checking for modules that export both
`__mailglass_mailable__/0` (discovery marker) and `__mailglass_opts__/0`
(compile-time opts reflection). Any module with `opens: true` or
`clicks: true` in its `:tracking` opts triggers the host check.

# `validate_at_boot!`
*since 0.1.0* 

```elixir
@spec validate_at_boot!() :: :ok
```

Raises `%Mailglass.ConfigError{type: :tracking_host_missing}` if any
loaded `Mailglass.Mailable` module has tracking enabled AND
`:tracking, :host` is unset or empty.

Returns `:ok` otherwise.

---

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