The salvaged proactive validation (#53307/#76896) rejects the
b'\x89PNG...' + zero-padding fixtures test_vision_tools.py used.
Replace all 11 sites with a real 1x1 PNG (+ ignored trailing padding
for size-sensitive tests), and pin _resize_image_for_vision passthrough
in the size-limit test so it exercises rejection, not resize recovery.
d48adfa789