My contracts always state I own tools created or byproducts of the work that don't end up in the work.
replyOnly if you are self employed, otherwise it belongs to the agency.
replyAgain: it depends. It is all about how the contract is written.
replyI never seen any other kind of contract, on my 50ys.
replyI'm curious how does it work, you handover the tools you wrote, .bashrc/.zshrc, etc?
replyWhen I'm hired in a company (not contract), they wipe the harddrive when I leave (well, I also do it before I hand it over sometimes). So they don't get the tools (I take them with myself, it would be a waste to loose them)
You're definitely right for most agencies; most will let you use it in a portfolio or something, but not necessarily retain the rights to the work.
replySome agencies do, however; it's dependent on the contract specifics.