A sash drag used to stop the moment its seam partner hit its min size, so a
row of panes behaved like unrelated boxes: growing the Browser tile could not
take space from Chat once the pane between them was at its floor. The drag
now plans the whole run from the pointerdown sizes — the partner donates
first, then its next visible sibling, and so on — and commits once on
release (fixed zones get px overrides, the flex run gets weights).
A reverse drag after a cascade stays local to the seam. Release only folds a
tool zone that THIS gesture took to its floor, so an unrelated rail already
resting there (a minimized Terminal) no longer cancels the Files/Chat commit.
Salvaged from #103166 (Jerry Gooch), trimmed to the sash-drag change; the
width/height lock feature, zone-body context menu and the restored-tool CSS
floor are held as separate decisions.
Jerry Gooch
e9c527eeb6