Slint negotiates a drag action between source and target, and the
runtime clamps whatever `can-drop` returns against the set the source
allowed: an action outside it becomes `none`. Both drop targets here
named a constant instead of echoing what was on offer, and each named
the wrong one for half its traffic.
A collection row takes two kinds of payload. Photographs come from a
DragArea allowing `copy`; a collection being nested comes from one
allowing `move`. The row asked for `copy` unconditionally, so images
filed correctly and every collection dropped on a collection was
refused — nesting by drag has never worked. The trash had the same
fault mirrored: it insisted on `move` while the grid's cells allow only
`copy`, so it refused every photograph dragged to it.
Neither failure had anything to see. A clamped action is delivered as a
refusal, which looks exactly like a target that declined on purpose, so
the drag simply did nothing and left no error to search for.
`decide_drop`'s Reparent branch was tested and passing throughout. It
tests the decision, not the negotiation, and nothing was reaching it.
dtourolle
577bbd82b0