[gohabereg]

What

Planning only: the add-data-node-operations OpenSpec change. It is stacked on #210, so review that one first.

Why

Data-node and value changes (DataNodeAddedEvent, DataNodeRemovedEvent, ValueModifiedEvent) stay local today: they aren't sent to collaborators and can't be undone. The v3 List tool depends on all of them, because it stores items as one flat array: items: [{ content, depth, checked? }]. Tab and checkbox toggles are updateValue, Enter inserts an array element, and a Backspace merge removes one.

What changes (summary)

• Model
  • Explicit createDataNode dispatches synchronously, with the author's userId. Today the event has none.
  • Data nodes created while a block is being built are marked isInitialization. Undo and collaboration skip them; adapters still get them, so data-first rendering keeps working.
  • modifyData handles DataIndex.
  • insertData on an existing object key replaces the node.
• Collaboration
  • The three events become Insert/Delete (payload: [subtree]) and Modify (payload / prevPayload).
  • New transformer rules for array positions: numeric key segments are array indices. Data and text operations inside a shifted element are re-keyed; operations inside a deleted element become Neutral.
  • Same-position ties and same-key conflicts use the explicit transform order from docs(openspec): propose fix for OT client/server divergence #210.
• Undo works in both the core and collaboration managers once the model replays these changes.

Out of scope

• Re-keying array elements in the model's node listeners and in InputsRegistry. That is a separate change and a hard prerequisite for List.
• Grouping several operations into one undo step in collaboration mode (listed as a follow-up in docs(openspec): propose undo grouping by browser task #201).
• Overlaps: with feat!: implement per-block plugin data #192 (both widen ModifyOperationData) and with docs(openspec): propose undo grouping by browser task #201 (whose R2 test relies on initialization events having no userId). Whichever lands second adjusts.

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