The terminal and logs carried a 7.5rem minHeight, so dragging the seam down
jammed against a floor with a sliver of unusable terminal still showing.
Tool-panel zones now floor at COLLAPSED_ZONE_PX (the h-7 header strip)
instead of the generic 80px, and releasing at that floor minimizes the zone
rather than persisting the sliver — it folds to its collapsed header,
vertical rail or horizontal strip depending on the parent axis. The sliver
size is never written, so restoring returns the height it had before.
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