Function affected_link_keys 

pub fn affected_link_keys<T, K>(
    plan: &ExtractorBatchPlan,
    previous: &[ExtractorBatch<T>],
    current: &[ExtractorBatch<T>],
    link_key: impl Fn(&T) -> K,
) -> Result<BTreeSet<K>, BatchPlanError>
where
    K: Ord,

Computes exact link neighborhoods affected by add, modify, and delete actions.

Modified sources contribute old and new keys, deleted sources contribute old keys, and added sources contribute new keys. Unchanged sources do not trigger relinking.

Errors

Returns BatchPlanError for duplicate source batches or when a changed action lacks the required previous/current batch.