Function remove_member 

pub async fn remove_member(
    pool: &PgPool,
    actor: &Actor,
    project_id: Uuid,
    user_id: Uuid,
) -> AppResult<i64>

Removes a member (managers and admins; everybody may leave a group). A manager cannot leave while no other active manager remains – an admin can still remove them. Returns how many check-outs the user still holds in the group.

Invariants

• Permission: the group is visible to the actor (“not found” otherwise); removing someone else needs a manager (or an administrator; 403), leaving needs nothing more.
• Locks: the group row (FOR UPDATE), so membership changes of one group are serialised.
• Data: a manager cannot be removed (nor leave) when no other active manager remains, except by an administrator (409); a membership synchronised from the identity provider cannot be removed here while its user is active (409) – a deactivated user’s can, since SSO refuses them and it cannot come back; a non-member is “not found”. Check-outs of the removed user are kept and only counted.
• Audit: project.remove_member.
• Notifications / webhooks: none.
• Atomic: one transaction.