Comment by eyelidlessness

> What safeguards around mutability does Clojure have?

Very nearly the entire language and standard library operate on immutable values only. Immutable values are the default, and you will use them for the vast majority of logic. You must do so, unless you very specifically opt to use dedicated reference types, at which point you’ll still need to produce intermediate immutable values to interact with that vast majority of the standard library.

And…

> is there any kind of contract, notation ... anything which could suggest whether it mutates or not?

Functions which mutate state are almost always suffixed !. They will typically fail if you pass them immutable values; they only operate on reference types, which have to be dereferenced (typically with the prefix @) to access their state.