This helps, though needs some update.
However, one important detail the verbose log cannot give is when these scripts run.
It looks like when an unit provokes reaction, first the engine determines that reaction should happen, then scripts run in the order reactionWeaponAction (if the action was with a weapon), then reactionUnitAction, then reactionUnitReaction.
But when does selectItemSprite run? Apparently not just once when the item spawns, since it can be used to react on ammunition changes. Every time anything is done with an item? Every frame the item is on screen?..
It’s obviously important for FooBonusStats, too, and not obvious either.
And so on.