So far, using RSA-PSS, it is caller's responsibility to prepare the input data like:

(data (flag pss)
  (hash <algo> <hashed-value>)
  (random-override <salt>))

with <HASHED-VALUE> (it is the caller who does hashing, beforehand).

It is good to have "prehash" function (in RFC 8032 (EdDSA) terminology) which hashes input internally when pk_sign-ed. The data format to use this functionality will be:

(data (flags pss)
  (hash-algo <algo>)
  (value <value>))