"""One directory per domain (D-263).

Each domain is split by role, and the split is what makes this a codebase that
shares rather than 123 scripts in twelve folders:

    router.py        CONTROLLER — args in, delegate, format out. No logic.
    service.py       LOGIC — transport-agnostic, importable by anything.
    schemas.py       this domain's data shapes (pydantic).
    helpers.py       domain-local pure helpers.
    dependencies.py  resolved collaborators (DB handle, paths, launchers).

The invariant that makes it work: `router.py` holds no logic and `service.py`
holds no Typer. A service must not know it was called from a CLI — that is what
lets one domain's service call another's, lets tests call services directly
without a CLI round-trip, and leaves a second front end possible without a
rewrite. It is also what keeps lazy loading achievable: routers are cheap,
services are not, and only the invoked domain's service is ever imported.

Not every domain needs every file. `schemas.py` and `dependencies.py` appear
when a domain has data shapes or collaborators worth naming. The layering is a
vocabulary, not a quota — a folder of five empty modules is worse than a folder
of two full ones.
"""