Slavic *kUznI 'art'

It seems that the PIE root *keuh2- 'strike' was reflected in at least
two Common Slavic verbs *ku"ti/*ko``voN (<-- **kU``voN ?) and *kova"ti
(<-- **kUva"ti ?)/*kûjoN (both 'forge'), much like *jeNtí/*jImò, and
*jIma"ti/*je``mjoN 'take'. On the other hand, Slavic deverbals in *-zn-
are unexceptionally formed from infinitive stems (z^i"znI 'life',
boja"znI 'fear'). We indeed have *ku"znja 'a forge' from *ku"ti, but
what does one make of *kUznI (a.p.?) 'art'? Is it derived from **kUtí,
later accreted with *-a"- to form **kUva"ti? And in what way can **kUtí
be derived from *keuh2-? Does one have to start from a form like the
3pl of the athematic present *kuh2énti > BSl. *kuwV- and then postulate
the infinitive *kutéi being analogical on the present? How are the
tricks usually done deriving Slavic infinitives from PIE stuff? Is
there a simple recipe or one has to consider every conjugational form
of every PIE verbal class (30+ in LIV2) to pick up a proto-form that
fits?

Sergei