movePanes/reorderPanesInGroup/mergeZonesWithPane now take a block of pane
ids in strip order: the lead pane decides the drop geometry (slot, split,
span-merge) and the rest stack in behind it, with the pressed tab fronting
at the destination. The tab-selection store holds the block (Chrome
grammar: toggle, anchor range, collapse on plain click), drag-session
carries it — every dragged tab dims, the insertion slot skips the whole
block, and a landed drop spends the selection while a deny-area release
keeps it for a retry.
Brooklyn Nicholson
cc8e97499c