We're back from the vet.
The lesion on Charlie's chest reopened, possibly because of ingrown feathers. After trimming away feathers, and pulling away the scab, the damned thing is about half the size of a dime.
They fitted him with an Elizabethan collar that is driving him mad, but it has to be done. He'll need stitches in a day or two, and he'll pick them right out without it.
She gave him a shot and did a topical treatment in case of infection.
UPDATE: Poor little Charlie. What did he ever do to deserve that collar, he wonders.