e128f1c131
A dragged session outlined every zone in the tree, including standing side chrome — the sidebar, files, terminal. None of them host a main tile, so the drop was always refused; the outline just advertised a target that wasn't one. Gate the overlay on the same isMainStripPane/isSessionStripPane test that tileZoneHost resolves the drop with, so what lights up and what commits can never disagree.