IntersectionObserver missed the case because scrolling inside the
nested .hwfit-list (max-height:52vh own scroller) doesn't move the
header out of view at all. The user wants any downward scroll in
the scan/download area to fold Direct Download.
Switched to a capture-phase scroll listener on #cookbook-modal that
catches every scroll event from any nested scroller (.hwfit-list,
.cookbook-body, .modal-content). Folds only on downward scrolls so
scrolling back up doesn't keep re-folding.
e630605aef