Function validate_repository_no_inline_retention 

pub fn validate_repository_no_inline_retention(
    _spec: &RepositorySpec,
) -> ValidationResult

A Repository spec does not carry kopia-side (repo-level) retention policy, which would conflict with CR-driven GFS retention (ADR §4.4 exclusivity).

The current RepositorySpec deliberately models no inline retention field, so this always passes today. It exists as the enforcement hook so that if a future field (e.g. spec.policy.keepDaily) is ever added, wiring it here is the one obvious place — and the rule is already named and tested. Be pragmatic: we do not invent a field to reject.