Last night, I put Tris on the longe line: sound at the walk and trot, a bit stiff at the canter but in a way that suggested to me he was just unbalanced and out of work, rather than hurting. Huzzah! He was also fresh - well, for him - and kept picking up a trot when I'd asked him to walk, and even gave me a little flourish in his transition into the canter.
The abscess site looks like it's healing well. I scrubbed it with betadine and soaked it, then iced his leg while getting my trailer ready to haul this weekend. The leg is still a bit spongy, but after chatting with J. I agree with her that it needs to be worked off at this point.
So, he will go back under saddle at the walk and have something of a rehab schedule, working up to trotting and cantering again slowly to make sure the leg clears up as we go along and he doesn't get stressed too much.
I'll keep soaking his foot through the weekend, and probably then hold off unless I see signs of a renewed problem. The abscess looks to be cleared up at this point, thankfully.