This has been a great week. First, Cupid's biopsy came back clean. Though we don't know the exact cause why that lump grew, at least it's not a tumor. For now I will just keep an eye on it for further changes. Removing it is a fairly minor procedure, but would primarily just be for cosmetic reasons (with a small benefit of avoiding him knocking it again.) If we have a bad fire season again and I'm not going to be riding or something like that, we may just get it done but it's not urgent.
But possibly even better news it for the last several rides Cupid's finally felt like his old self, no crankiness much happier to go forward. Whatever was bothering him seems to have resolved. He's been on GutX for over a month so maybe it was that. Or just kind of resetting our relationship with contact (taking it away completely for a while then slowly building back). Or just some other body soreness.
He feels active and engaged, I don't have to chase him into a canter, and can actually shorten and lengthen his trot a bit. I'm feeling pretty happy and optimistic for the first time in months!