I just finally read the whole thread. There are some good suggestions, but it seems that about 60% recommend the XA, another 30% recommend the Hexar, and 10% other things.
I guess it comes down to what you want in stealth shooting. If you don't want someone to see or hear the camera, the XA wins, hands-down. Sure the Hexar has a quiet shutter and film advance, but it is HUGE compared to the XA.
Another thought would be Rollei 35. That one has character; a lot of us love ours. This one is also big compared to the XA, and forces/allows you to set exposure manually. Quiet shutter, but louder than the XA. Quite a bit more lumpy with more protrusions. It would look funny in a shirt or pants pocket.
Another thought: Olympus XA4. These are bloody hard to find, but have a 28mm lens, so zone focusing is even easier.
Lastly, Olympus RC. I don't know yet how the lens compares to the XA, but I bet it's better since it is the same speed but isn't so compact. It's a little bigger than the XA & Rollei 35, but still small, and it feels kind of like a tiny SLR in the hand. (and control layout)
I love these little fixed lens rangefinders/scale focusers. Less is more! 😉 It's amazing, the quality optics you get for such a small amount of money.
-Jeremy