Is there a cache for XQuery code? I work with small snippets and can
most of the time choose if something is a literal or passed as an input
variable.

If you want to resort to the string representation of a query, you could store it in the cache as well, and evaluate it later on, e.g. as follows:

'name-of-query'

=> cache:get()

=> xquery:eval()

Query strings could also be organized in an XQuery map:

(: run cached query :)

let $map := cache:get('queries')

let $query := $map?name-of-query

return xquery:eval($query)

(: register query :)

'123 + 456'

=> cache:get('queries')

=> map:put('name-of-query', $query)

=> cache:put()