Poll. So, what exactly is Hit&Run?

Hit-and-run is prohibited: the attacking hero is not allowed to retreat in the first round of battle if they cast any spell. This prohibition does not apply to the hero who is defending.

+1.
1) Unambiguous interpretation - no additional entities are created - direct damage spells, etc. (all these nuances should be within the rule)
2) Simplicity of interpretation - as mentioned above, the simpler, the better...

What if the attacker has a spellcasting stack? Does this need to be clarified? It seems that the spell is cast not by the hero, but by their units?

Based on the principles outlined above, retreating is also not allowed; the spell was cast, even if it was done through a spellcasting unit and not manually, through a spellbook.

There is no impoverishment of the game; it simply means that we now need to consider the possibility that this unit may have to be sacrificed, and that's all:). You cast a spell yourself - let another cast a spell for you;).