I am late to this thread. What a terrifying situation. A friend of mine took a washed out show jumper and turned her into a solid 3rd level dressage horse. However, you could NOT warm her up in any size arena that even had jump standards in them. This was a kind and generous tempered mare who had been so serially abused about jumping that she absolutely had ptsd about it and never got over it, even 10 years after she bought her. Her mind just left. To her credit all she would do was pick up a quick canter and stay in it until she navigated her mind’s panic until she found her way out of it, which might be one lap it might be 12. She was robotic and unavailable to her rider in any way.
OP - I hope that this thread is found by anyone who looks at this horse. Regardless of his problems and however they came to be, no one should think he’s safe to ride and needs to know he will need extensive rehab and training and he still may be a pasture puff.
You’re an experienced rider and you were seriously injured by him (not saying he’s malicious!) and it sounds as though you don’t want anyone trying him to not take every precaution and still be prepared for him to react strongly and without warning.
May you heal quickly and completely. May he land softly.