Function look_up_person 

pub async fn look_up_person(
    ctx: &ManualActionContext<'_>,
    student_number: &SecretString,
) -> Result<Option<RegistryPerson>, PersonLookupError>

Looks one student number up in the study registry without changing anything: no ledger row, no claimed mail slot, just the call log row every study registry call writes.

Ok(None) means the registry answered personNotFound; Err means it gave no usable answer.