thanks for the kind words
@biophiliac!
as for the OP, I agree, it sounds like a meat bird. the runny poop has a lot to do with the super high protein diet they are given, causes them to go hypotonic. was probably given 22%, if you lower it a bit, say 19% things will firm up. that said, you are not likely going to be able to add this one to your flock long term. the CX live life in fast forward, gaining tremendous weight and when they reach slaughter weight, they quickly go south health wise. with just the right coddling you can get them to live a year or two but I'm not sure it's worth it. you did save this bird from misery and that is honorable even if you end up putting it down and having it for dinner, it was in the road and sure to meat an unflattering death. the cornish cross results in a bird that really isn't all that happy as an adult, there are many strains, and some are much more lively than others, but the one the meat industry tends to go for is the one that sits, eats and gains weight the fastest at the expense of a humane life. they often don't even fully feather out, staying partially bare skin. you can grow your own in a much more humane way, and if you go that route, as I did, much for the same reasons as you are talking, I'd recommend going with the COBB 500 strain of CX. it feathers out, plays around, digs, flaps and runs like a normal chick. it will eventually get very heavy but can live a decent, all be it short, life. we love our CX and they are amazing at efficiently converting grain to meat for my family of 4.
it's a pleasure to welcome a new member who takes action to help a bird in distress, even when it's inconvenient.
Has some cuteness overload pics of the recent babies 'livin the good life' 
. I think one key to success is the use of aged wood chips as litter for poop management.
