You asked for Edmund asks and I'm here to deliver. Sorry if this really surface level or straight up wrong, I am but a normie when it comes to enjoying Shakespeare. So there's before the scene where Gloucester gets blinded, Edmund is sent away by Cornwall and it felt like a missed opportunity to make him prove his loyalty. Eventually, I assumed Cornwall didn't want him backpedaling and that got me wondering, would he? I mean, would it have changed anything if Edmund was in the room or tasked with blinding Gloucester? On one hand, Gloucester's situation is of Edmund's own design, it's not like he doesn't know how serious treason is. On the other hand, he may not like or respect him much but he still craves his approval and it makes me wonder what would change if he was holding the blade.
in short, I think bringing Edmund along for Gloucester's interrogation would be counterproductive on many levels.
For the most surface level explanation, at this point Gloucester didn't know that Edmund betrayed him. He still believes Edmund is a good and loyal son. If there's any chance of him surviving the interrogation and getting away (as he does), you would want to have someone who he trusts to keep him under control.
standard 'playing politics' move.
During the interrogation -- Regan, after Cornwall is stabbed and Gloucester's eyes are out, reveals that Edmund has betrayed him. It doesn't seem like this was part of the original plan, and this ultimately ends up costing Edmund his life.
On the topic of Cornwall potentially needing Edmund to prove his loyalty-- the only thing being involved in Gloucester's torture would prove is that Edmund hates Gloucester. Which he already knows, as he heavily implies he's aware that Edmund's intentionally destroying the Gloucester noble lineage to become earl. And he thinks that that's very cool of him :)
On top of all that, dragging Edmund into the interrogation is not the role he want to play here. Whatever he's got going on here-- "thou shalt find a dearer father in my love" -- again, this is another political move. He recognizes what Edmund is capable of, and most likely wants to use this new connection he has to him. Edmund turned to him to denounce Gloucester as a traitor, and Cornwall wants to play the role of Edmund's 'savior' who removes this 'awful evil traitor' Edmund was 'brave enough' to denounce.
Him sending Edmund away before the torture could be a way of saying 'don't worry, I've got this covered from here.' He's choosing to actively take a part in Edmund's ascent to the Earldom, proving allegiance to the brand new earl of gloucester.
in short. the torture functions more as Cornwall proving his loyalty to Edmund's cause than any potential loyalty test for Edmund.
and of course imma shout out @suits-of-woe's Cornwall analysis posts-- he understands Cornwall on a level deeper than I could ever hope to, and I feel like reading his Cornwall Analysis Saga should be required text for anyone playing Cornwall
