Grant Seat

Give a member access to an app. The Stripe subscription quantity is reconciled asynchronously, so billing always matches assigned seats. A grant past the seats paid for is 409 seat_limit_reached, even while seats grow as people join: that growth is for a newcomer’s own default seats, never for a grant. Grants at the same moment are counted one after another, so two cannot share the last seat. A member on the app’s waiting list comes off it once given a seat.