Function set_member_expiry 

pub async fn set_member_expiry(
    pool: &PgPool,
    actor: &Actor,
    project_id: Uuid,
    user_id: Uuid,
    until: Option<NaiveDate>,
) -> AppResult<()>

Sets or clears when a membership is meant to end (“member until”, issue #173 step 8). Only a flag on the season page: nothing removes the member when the date has passed.

Invariants

• Permission: the group is visible to the actor (“not found” otherwise) and the actor manages it (or is an administrator; 403).
• Locks: the group row (FOR UPDATE), as the other membership changes.
• Data: the user is a member (“not found” otherwise).
• Audit: project.member_expiry.
• Notifications / webhooks: none.
• Atomic: one transaction.