The app-level profile -> Connection pid registry: the seam that enforces one connection per profile and lets a consumer refer to a connection by its :profile (restart-safe) rather than a raw pid.

Reach = the registry module's reach

By default this is a local Elixir Registry (this module name doubles as the default registry's process name, started by Amarula.Application), so uniqueness is enforced per node. A clustered consumer can supply a different, :via-compatible registry via the :registry connection config — e.g. Horde.Registry for cluster-wide uniqueness:

Amarula.new(%{profile: :primary, registry: {Horde.Registry, MyApp.HordeReg}})

The :registry config is {module, name} (or just name, defaulting the module to Registry). The library only relies on the standard Registry/:via contract (register/3, lookup/2, {:via, mod, {name, key}}), so any module implementing it works without a code change here.

Uniqueness is keyed by profile and is the consumer's responsibility: the library trusts profile <-> credentials 1:1 and does not validate it.