The thread query is an infinite one and the frontend logic is
based on the structuralSharing concept of react-query to
optimiscally update the react query cache on thread mutation in
order to improve ux. This part is a tricky one and it's easy to
introduce regression, that's why refactor it by moving the corresponding
logic into a mailbox-cache module, use a better naming (pin instead of optimistic)
and battle test it.
