Slate v2 set_node needs prop-preserving draft and snapshot paths

What happened

The next slate op-family slice looked small on paper:

• add set_node
• add Transforms.setNodes(...)

The first red showed the real problem immediately: replacement snapshots were already dropping custom node props.

That meant a shallow setNodes wrapper would have been fake. Even if the op existed, the runtime would still erase custom props when nodes moved through draft and snapshot paths.

What fixed it

The honest fix had two parts:

1. add a real set_node operation and path-based Transforms.setNodes(...)
2. preserve custom props through the current draft/snapshot seam

That required keeping props alive through:

• createDraftTree(...)
• materializeSnapshot(...)
• descendant cloning
• text splitting helpers
• the current normalization path for adjacent text nodes

The key rule for normalization was simple too: adjacent text nodes should only merge when their custom props still match.

Reusable rule

For Slate v2 node-property updates:

• never add set_node on top of a draft model that already drops props
• if snapshots erase custom props, the transform API is lying
• prop-preserving draft/snapshot paths are a prerequisite for honest node-property transforms
• text normalization must respect formatting props when deciding whether adjacent text nodes can merge

If a node-property API lands before those rules hold, it is not a feature. It is debt with a nicer name.