A spearmen unit has only its front rank left of 3 trays. The middle tray contains a wounded front line rune golem. 22.4 prevents the last point of damage being assigned to the rune golem until at least one flanking tray is removed. Golden rule says cards over rule rules reference. Executioner states that you can select a wounded figure you are engaged with and remove it. If this sequence is valid, then there is no rule to combine the split unit. If the rune golem is not a valid target at this time by executioner then the golden rule is incorrect?! Thoughts?

The front rank is also the back rank when thete is only one rank (see Rank in the rules reference). The Learn to Play guide says somewhere that if a heavy upgrade is removed, you replace it with a tray from the back. Since the front is the back, you would move one of the remaining trays over to where the Rune Golem was.

(On mobile, so sorry I don't have references.)

Rule 66.1. Missed that one.