Function detect_repository_identity_change 

pub fn detect_repository_identity_change(
    old: Option<&IdentityDefaults>,
    new: Option<&IdentityDefaults>,
    acknowledged: bool,
    consumers_with_history: &[String],
) -> Option<ValidationError>

Pure decision for the repository identityDefaults-edit guard. An edit to a Repository/ClusterRepository’s identityDefaults (cluster, hostnameExpr, or usernameExpr) changes what every consumer SnapshotPolicy relying on those defaults resolves to — silently, with no per-policy edit to acknowledge it (unlike detect_identity_fork, which guards a policy’s own edit). Returns Some(ValidationError::RepositoryIdentityWouldFork) iff identityDefaults actually changed, at least one consumer has snapshot history, and the change is not acknowledged. The webhook does the IO (list consumer SnapshotPolicys, read the ack annotation) and calls this.

use kopiur_api::common::IdentityDefaults;
use kopiur_api::validate::detect_repository_identity_change;

let old = IdentityDefaults { cluster: Some("east".into()), ..Default::default() };
let new = IdentityDefaults { cluster: Some("west".into()), ..Default::default() };
let consumers = ["billing/pg".to_string()];

// Change + a consumer with history + no ack → rejected, naming the consumer.
assert!(detect_repository_identity_change(Some(&old), Some(&new), false, &consumers).is_some());
// No consumers with history → nothing to orphan → allowed.
assert!(detect_repository_identity_change(Some(&old), Some(&new), false, &[]).is_none());
// Acknowledged → allowed.
assert!(detect_repository_identity_change(Some(&old), Some(&new), true, &consumers).is_none());
// No actual change → allowed.
assert!(detect_repository_identity_change(Some(&old), Some(&old), false, &consumers).is_none());