UpdateDataModelMessage
@Serializable
Writes value into a live surface's data model.
path is a JSON Pointer; omitting it, or passing /, addresses the whole data model. It is carried verbatim and is NOT checked for pointer syntax here — it arrives from the agent and is the write address into the data model, so validate it before resolving it.
A value of kotlinx.serialization.json.JsonNull deletes what path addresses, which is why this is a non-null JsonElement — an absent value is malformed, an explicit null is a delete.