The contract a host module implements to hook into comments.

Every callback is optional and every one is invoked through function_exported?/3, so a module may implement one, some or none — @behaviour here buys compile-time checking of the ones you DO write, which duck-typing never did. Before this existed the six-callback contract lived only in a moduledoc, so a typo in a callback name (or drift in its arity) produced silence: the callback simply never fired and nothing said why.

Adopting it is opt-in and non-breaking — handlers registered today keep working untouched.

defmodule MyApp.Orders do
  @behaviour PhoenixKitComments.ResourceHandler

  @impl true
  def resolve_comment_resources(uuids), do: ...

  @impl true
  def on_comment_created(_type, _uuid, comment), do: ...
end

Paths are RAW

resolve_comment_resources/1 returns path WITHOUT the PhoenixKit url prefix — the renderer applies Routes.path/1 once. A handler that pre-prefixes gets a doubled prefix.