Yeah, we always wonder what he had to deal with. He's still very sensitive to any pressure at all on his ribs, and he hoards soft toys in a den (under a bed), though he responds with exasperation rather than anger if one is taken. When we first got him, he tried eating acorns (hell on a dog's stomach, I understand), pre-emptively winced the first time he barked in view of me, and despite generally hating to go outside any longer than it took to potty, climbed up on our patio furniture to investigate the fence the first time we had to leave him with a sitter.
These days, he's fat, which is a negative of course, and he's still an idiosyncratic homebody, but he's also confident enough to ask for affection, isn't reactive to anything other than vacuums, and has a great relationship with our other dog. The turnaround has been lovely, and if being a chonk came as part of it, I think it's a trade worth having made. Our other rescue was born after his mother arrived at the foster, and has a very different relationship with food, exercise, and new people. His super playful but emotionally aware energy has worked well with our "seen some shit" heeler.
Between the thousands of years of semi-selective breeding and the parallel evolution that made our ancestors want the selective breeding to happen, the emotional compatibility between dogs and humans is amazing. They're not humans of course, and we do well to remember that, but the connection is eerie, and when you see a dog display that kind of pack/family oriented behavior, it's heartwarming.
We have a dogsitter when we are on trips. According to her, our heeler would politely take blueberries that were offered and then wander off, returning not long after. It was only later that she found a stash of uneaten blueberries on the couch. My little man was a desperately skinny and frightened stray in a kill shelter before he came to us, and on the theory that whatever makes him feel safe and content is better than the alternative, he's, uhhh, put on weight. If he liked the blueberries, they would not be left on the couch.
This dog is very polite (startrek.website)
Dame Judi Dench dressed like Darth Vader at my condo (lemmy.world)