is_element_visible_according_to_all_parents mutated snapshot_node.bounds in
place while walking the frame chain, permanently shifting every checked
node's coordinates by frame offsets and scroll — corrupting values shared
with absolute_position math, paint-order filtering, and any later visibility
check (the function was not even idempotent).
Worse, a frame node appears in its own frame chain (_construct_enhanced_node
appends it before computing visibility), so an iframe's bounds were offset
by themselves — coordinates doubled — wrongly classifying iframes past
half the viewport threshold as invisible and silently dropping their entire
content subtree from extraction.
Work on a copy of the bounds and skip self in the frame chain.
Saurav Panda