Converts a Cooper.load_file/2/Cooper.load_string/2 result (a string-keyed map, CASC blocks nested arbitrarily deep) into the [app: [key: value, ...]] shape Application and Config.Provider expect.

Each map -- at every nesting level, not just the top two -- becomes a keyword list with atom keys, so the result deep-merges against existing app config the same way multiple config.exs files merge (Config.Reader.merge/2 only deep-merges when both sides are keyword lists; a plain map would replace wholesale instead). Lists and tuples are walked element-wise but keep their own shape; every other value (numbers, strings, atoms, booleans, Cooper.IPv4/Cooper.IPv6, duration/byte-size tuples, ...) passes through unchanged.

Secrets

A Cooper.Secret-wrapped value is revealed (Cooper.Secret.reveal/1) by default, since Application/release config has always held raw secrets in ordinary Mix config (System.fetch_env!/1 in runtime.exs, for example) and most consumers of app env (Ecto, Plug.SSL, ...) expect a plain value, not a wrapped one. Pass reveal_secrets: false to keep values wrapped instead -- consuming code then needs Cooper.Secret.reveal/1 at the point of use, trading drop-in compatibility for the same accidental-leak protection Cooper gives everywhere else.

A note on atoms

Every map key becomes an atom via String.to_atom/1, same posture as Cooper's own handling of CASC atom literals (see its moduledoc): fine for config sourced from a fixed, trusted set of files, not something to point at untrusted input.