ML configuration system with inheritance and validation

class Field:
    def __init__(self, type_, default=..., choices=None, min=None, max=None): ...


class ConfigError(Exception):
    def __init__(self, errors): ...


def merge(base, over): ...                                   # dicts merge, lists replace, None deletes
def resolve(name, registry, schema, overrides=()): ...       # base chain, CLI overrides, ${refs}, validation
def validate(cfg, schema, prefix=""): ...                    # -> list of "path: problem"
def config_hash(cfg): ...