Multiple Tree Demo inconsistent behavior, buggy.

[waml]

Describe the bug
try moving item from one tree to another node, when you click expand, it seems to create duplicates in the new tree. Also it causes indentation of the other parent node which is unrelated, leading to confusion. in some cases the entire tree disappears.

To Reproduce
It's hard to list all permutations but a simple one: try moving lunch into the other lunch tree. the other tree disappears. try moving from one to another.

Expected behavior
moving items from one tree to another should be consistent and bug free

Screenshots
No screenshot but saw the console output:

Uncaught (in promise) InternalError: too much recursion
    key https://headless-tree.lukasbach.com/storybook/react/9378.e0cad722.iframe.bundle.js:1
    retrieveChildrenIds https://headless-tree.lukasbach.com/storybook/react/guides-multiple-trees-stories.3de8d61f.iframe.bundle.js:2
    key https://headless-tree.lukasbach.com/storybook/react/9378.e0cad722.iframe.bundle.js:1
    recursiveAdd https://headless-tree.lukasbach.com/storybook/react/9378.e0cad722.iframe.bundle.js:1
    recursiveAdd https://headless-tree.lukasbach.com/storybook/react/9378.e0cad722.iframe.bundle.js:1
    recursiveAdd https://headless-tree.lukasbach.com/storybook/react/9378.e0cad722.iframe.bundle.js:1
    recursiveAdd https://headless-tree.lukasbach.com/storybook/react/9378.e0cad722.iframe.bundle.js:1
    recursiveAdd https://headless-tree.lukasbach.com/storybook/react/9378.e0cad722.iframe.bundle.js:1
[9378.e0cad722.iframe.bundle.js:1:660](https://headless-tree.lukasbach.com/storybook/react/9378.e0cad722.iframe.bundle.js)
Uncaught TypeError: item.getItemMeta() is undefined
    onClick 9378.e0cad722.iframe.bundle.js:1
    Nb index.mjs:197
    Tb index.mjs:197
    Ub index.mjs:197
    nf index.mjs:197
    se index.mjs:197
    hd index.mjs:197
    Rk index.mjs:197
    Jb index.mjs:197
    hd index.mjs:197
    fd index.mjs:197
    ed index.mjs:197

Additional context
mac os, firefox

[lukasbach]

Hey, thanks for the report! There were two underlying problems that caused this:

First, HT triggering recursion loops if items are duplicated because they exist redundantly in multiple trees, and then are dragged from one tree into another into an item of the same key: I've updated the sample storybook so that both trees don't have the same items anymore, but also added a check in the implementation so that, if a subtree contains a recursively redundant item, the redundant item and everything below is ignored when rendering, to introduce some additional resiliance. But ideally, real trees shouldn't contain the same item on multiple trees.

Second, kinda as a consequence of the first, the sample fails to model a use case where both trees have distinct data sources. In the old sample, both trees used the same data source and the same items, which means that just updating children IDs would suffice when dragging items from one tree to another. In cases where data sources are distinct, the target data source would have to be updated with the newly dragged in items.

Unfortunately, this is hard to solve at a library-level, since the data source is mostly consumer-concern. I've added additional docs on this (https://headless-tree.lukasbach.com/dnd/foreign-dnd#interactions-between-multiple-instances-of-headless-tree) with how to approach this, in the simplest case both trees still use the same data source but different root IDs, the same way how it worked in the past in react-complex-tree, and this is certainly the easiest to implement. In cases of truly distinct data sources, the user has to implement logic to move the data of moved items along the item IDs, and insert them into the new data source on the drop event, which I have added in the docs in the "Advanced Multiple Trees" Storybook sample.

[lukasbach]

Since I don't see any more actionable next steps for this, and since I've created some additional docs and samples on how to approach this, I'll close this for now. Please reopen or create a new ticket if something else comes up. Thanks!