Bug: Reconciler does not insert a managed line break into ElementDOMSlot

[levensta]

Lexical version: 0.49 latest

Steps To Reproduce

1. Define an ElementNode with the getDOMSlot method
2. Insert a node with text content into the editor
3. Delete the text content

Link to code example: https://codesandbox.io/p/sandbox/3xpqzc

The current behavior

When a node with a DOM slot is empty, it lacks a managed line break, so node visually collapses as if it had been completely removed

Screen.Recording.2026-08-12.at.02.04.51.mov

The expected behavior

A managed line break is set if the DOMSlot is empty, similar to the standard DOM structure for an ElementNode

Impact of fix

It would be better if the managed line break were handled entirely by lexical

[levensta]

Here's another question, but this one is related to named slots. Using the same example, I see that a named slot is mounted as the last child element of the node's container. But if the content of the slot's node is updated, the slot's position in the DOM changes to the first child. Why is that?

Screen.Recording.2026-08-12.at.02.11.46.mov