Open-world stateful in-memory Repo handler for tests.

Thin wrapper around DoubleDown.Repo.OpenInMemory that provides skuld's effect-based with_handler/3 API. The underlying DD fake handles all Repo operations — writes mutate state, PK reads check state then fallback, everything else goes to fallback.

For most use cases, prefer Repo.InMemory (closed-world) which is authoritative for all bare-schema reads without a fallback. Use OpenInMemory when the state is deliberately partial.

Usage

alias Skuld.Repo

# Basic — PK reads only, no fallback:
comp
|> Repo.OpenInMemory.with_handler(Repo.OpenInMemory.new())
|> Comp.run!()

# With seed data and fallback:
state = Repo.OpenInMemory.new(
  seed: [%User{id: 1, name: "Alice"}],
  fallback_fn: fn
    :all, [User], state ->
      Map.get(state, User, %{}) |> Map.values()
    :get_by, [User, [email: "alice@example.com"]], _state ->
      %User{id: 1}
  end
)
comp
|> Repo.OpenInMemory.with_handler(state)
|> Comp.run!()

Extracting Final State

Use the :output option to access the final handler state:

{result, final_store} =
  comp
  |> Repo.OpenInMemory.with_handler(Repo.OpenInMemory.new(),
    output: fn result, state -> {result, state.handler_state} end
  )
  |> Comp.run!()

Fallback function

The fallback function receives (operation, args, state) where state is the clean store map (without internal keys). If it raises FunctionClauseError, dispatch falls through to an error.

This is the skuld-idiomatic 3-arity convention. The wrapper adapts it to DD's 4-arity (contract, operation, args, state) convention internally.