Harden Return Trip Logic for Detached Items

[tobiu]

Scenario:

1. User drags item from Window A (Source).
2. Item becomes a Popup (Window C).
3. User drags Popup over Window B (Target). Proxy appears in B.
4. User changes mind and drags back to Window A.

Risks:

• Does Window A recognize the item as its own returning child (via detachedItems map)?
• Does it create a duplicate?
• Is the state (internal component data) preserved through the round trip?

Goal:
Audit and harden this flow. Ensure onDragBoundaryEntry in the Source correctly identifies the returning item and restores it to its original state/placeholder without data loss or ID conflicts.