The 5th-level cleric and 4th-level paladin spell mark of justice curses the subject when the subject performs an action chosen when the spell is cast. Is there a similar spell for punishing unruly behavior available to a druid? Official preferred, but, if unavailable, third party or homebrew versions are acceptable as are very simple methods of adding the spell mark of justice to a druid's spell list.
"Why?" or "A druid doesn't need mark of justice to punish the unruly. A druid punishes the unruly by eating them"
I like cats, but my experiences with them lead me to believe (perhaps erroneously but hear me out) that few cats would take the feat Healing Chi unless taking the feat were somehow incentivized. For example, a sufficiently persuasive druid capable of communicating with a feline beforehand might convince the typical cat to say it will take the feat Healing Chi upon being the subject of the spell awaken, but the cat could, upon becoming sentient, change its mind (as cats are wont to do and, incidentally, making the cat's previous statement not actually a lie—I imagine cats equivocate quite a bit). A mark of justice spell keyed to activating if the cat picks as its next feat a feat other than Healing Chi would be just the thing for keeping such a suspiciously mercurial cat in line.
But druids can't cast mark of justice (nor lesser geas et al., which is limited to bards, sorcerers, and wizards), yet there should be a spell available to druids for enforcing such agreements.
Threatening to kill the cat if it doesn't take the feat upon being the subject of the spell awaken—and following through to make an example of it for the benefit of other cats that may be watching—is a nonstarter. Just so you know.
(Note that it's possible the cat doesn't gain a feat from the two additional Hit Dice added by the spell awaken, as such a cat has 2½ Hit Dice rather than 3. If that bothers you, replace in the previous explanation the cat with a serval (Sandstorm 194-5).)