"""Shared substrate — only what has no domain (D-263).

config, paths, errors, console output, process launching. Nothing else.

The bound is deliberate and it is the rule most likely to erode invisibly: the
moment a module in here grows a service — its own logic, its own data store, its
own verbs — it is a domain and it moves to `tooling.domains`. A `core/` that
accumulates services becomes a package everything imports and nobody can change,
which is the worst possible shape for the one directory meant to be stable.
"""