Function validate_repository_health 

pub fn validate_repository_health(
    health: Option<&RepositoryHealthSpec>,
    context: &str,
) -> ValidationResult

spec.health rules shared by Repository and ClusterRepository (ADR-0005 §13). The index-blob warning threshold must be non-negative: a negative count is nonsensical, and 0 is the documented sentinel that disables the warning (so it is allowed). context names the kind for the message (“Repository” / “ClusterRepository”).