Dragging a location asset next to another makes it a child

Problem/Motivation

Originally described in https://www.drupal.org/project/farm/issues/3231161#comment-14308054: →

In the process of testing, I discovered another bug as well when trying to drag an item out of a parent and back into the root context ("All locations"). It works fine if you drag the item on top of the "All locations" item directly, but if you try to drag it NEXT TO an item under the "All locations" item (so that it is also a child of "All locations"), and then save, the item ends up under whatever parent item you dragged it NEXT TO.

I traced this with console.log()s and it seems to be an issue with Inspire Tree's node.drop event. In the situation described above, the target node that you get in tree.on('node.drop', function(event, source, target, index) is NOT "All locations". It is the item you dragged it NEXT TO. Inspire Tree doesn't seem to return the correct target in that case.

I found this old bug report which seems to have an important clue: https://github.com/helion3/inspire-tree-dom/issues/20

targetNode is the node being targeted by the user

"node being targeted" may mean "node that the item is next to" in this case.

This is a bit hard to trace currently because we are using UUIDs, so I tweaked the code locally to use asset IDs instead, and that makes it very clear what's happening. However, I can't find a good solution. It seems like a bug/limitation with Inspire Tree itself.

Steps to reproduce

In the Locations hierarchy editor (/locations) drag an asset so that it changes position relative to other assets in the same level (do not change its parent). Save. Reload the page. The asset is now a child of the asset it was moved next to.

Proposed resolution

This seems to be an upstream issue with Inspire Tree. I'm not sure what the right solution is.

Remaining tasks

TBD