Glazer

Targets are picked before the attack sequence starts. See Picking Targets on page 6 to the core rules, and Making Attacks on page 7. Important quotes are: "When unit shoots or fights, you must first pick the target unit(s)... before any of the attacks ... are resolved." and "Attacks are resolved one at a time using the following attack sequence." Hope that helps!

Check out this article (especially towards the end where it addresses balance): https://www.warhammer-community.com/2019/07/22/warcry-preview-campaigns/

There is this from the core rules design comments for Reserves: "Q: Some abilities allow you to remove a unit from the battlefield and set it up again, and say that this ‘counts as their move for the movement phase’ (or words to that effect). Do these units count as having made a move for the purposes of any other rules or abilities? A: No, it simply restricts them from making a move later on." Hope that helps!

Just for the record, the precis of the Soul Cage rule in the OP is not what appears in the Nighthaunt book. Here is the text from Nighthaunt (note the emphasis on the word fight): 'Soul Cage has a casting value of 6. If successfully cast, pick an enemy unit within 12" of the caster and visible to them. Until the start of your next hero phase, that unit cannot retreat. In addition, until the start of your next hero phase that unit cannot fight in the combat phase unless all other enemy units that are eligible to fight have already done so.' TLDR Soul cage says fight, not attack.