# `Accrue.Application`
[🔗](https://github.com/szTheory/accrue/blob/accrue-v1.0.0/lib/accrue/application.ex#L1)

OTP Application module for Accrue — manages boot-time validation and
the supervision tree.

## What this is

Accrue follows an empty-supervisor pattern: it is a library, not a
service. The supervisor starts with no children. Accrue does **not**
start host-owned processes such as your Repo, Oban, ChromicPDF pool, or
Finch pool — your application's supervision tree owns those.

## What happens at boot

Before the (empty) supervisor starts, Accrue runs several validations:

  1. **Config schema check** — `Accrue.Config.validate_at_boot!/0`
     validates the `:accrue` application environment against the
     NimbleOptions schema. Misconfiguration fails loudly at startup,
     before any state is touched.

  2. **Auth adapter safety check** — `Accrue.Auth.Default.boot_check!/0`
     refuses to start in `:prod` when `:auth_adapter` still points at
     the dev-permissive default adapter.

  3. **PDF adapter availability check** — warns at boot if
     `Accrue.PDF.ChromicPDF` is configured but no ChromicPDF supervisor
     child is running in the host app's supervision tree.

  4. **Oban queue / PDF pool size check** — warns if the `:accrue_mailers`
     Oban queue concurrency exceeds the ChromicPDF pool size, which can
     cause back-pressure on invoice email rendering.

  5. **Connect webhook secret collision check** — warns when a Connect
     endpoint's webhook signing secret is byte-identical to a platform
     endpoint secret. Stripe issues a separate signing secret for Connect
     endpoints in the Dashboard; mixing them causes silent signature
     verification failures. See `guides/connect.md`.

  6. **Company address / locale check** — warns when customers have
     EU/CA preferred locales but `:branding[:company_address]` is unset.
     CAN-SPAM/CASL require a physical postal address in transactional
     emails for those locales.

## Host app integration

`Accrue.Application` is started automatically by OTP when `:accrue` is
listed as a dependency — host applications do **not** start it manually.
Ensure your `config/runtime.exs` is complete before the application
starts, as validation runs during `start/2`.

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