Function set_visibility 

pub async fn set_visibility(
    pool: &PgPool,
    actor: &Actor,
    id: Uuid,
    visibility: ProjectVisibility,
) -> AppResult<Project>

Restricts a group to its members or opens it to all users again (managers of the group and administrators).

Invariants

• Permission: the group is visible to the actor (“not found” otherwise) and the actor manages it (or is an administrator).
• Locks: the group row (FOR UPDATE); item creation holds it FOR SHARE, so no number is drawn while the counters move.
• Data: opening the group merges its private number counters back into the shared ones; the same visibility again changes nothing.
• Audit: project.visibility.
• Notifications / webhooks: none.
• Atomic: one transaction (tests/atomic_processes.rs).