Resolves the Ecto repo used by Attached.

Normally an internal concern — Attached's own context modules call current/0 to pick up the host app's repo. Exposed publicly for the rare case where a caller needs the same resolution logic (e.g. a dashboard or maintenance script).

Configuration

Static repo — the common case:

config :attached, :repo, MyApp.Repo

Dynamic resolution — for multi-tenant apps with per-request repos:

# mod/fun
config :attached, :repo, {MyApp.Tenant, :current_repo}

# capture
config :attached, :repo, &MyApp.Tenant.current_repo/0

Without explicit config, Attached falls back to the first :ecto_repos entry of any loaded application — convenient for single-repo apps where you haven't wired Attached up yet.

Why no per-call :repo option?

Previous versions accepted repo: MyApp.Repo on every public function. That pushed repo plumbing into every caller for the sake of a feature (dynamic repos) most apps never use. The callback config above covers the dynamic case without polluting the API.