Function holdings 

pub async fn holdings(
    pool: &PgPool,
    actor: &Actor,
    user_id: Uuid,
) -> AppResult<Holdings>

The holdings of a user as actor may see them.

Invariants

• Permission: administrators, and managers of at least one project group (403 otherwise); an unknown user is “not found”.
• Visibility: every list is filtered with the guards of services::access for the actor; a manager additionally sees only what lies in the groups they manage (items without a group are for administrators). Check-outs in groups hidden from an administrator are a count per group, without item numbers. Tokens are for administrators.
• Data: read-only; at most MAX_LIST entries per list.