…sion`

…n 0 guard

…ples

Introduce a provider-agnostic Versioning extension with in-memory backend,
Yjs-specific versioning adapters for both yjs and @y/y, a new YjsThreadStore
for comments, and three new versioning examples (yjs13, yjs14, standalone).
Update ForkYDoc, ExtensionManager, and React versioning components accordingly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

…, and comprehensive tests

- BlockContainer content spec: change suggestionBlockContent? to * for
  multiple suggestion nodes
- getBlockInfoFromPos: track suggestionBefore/suggestionAfter, add
  isSelectionAtBlockStart/isSelectionAtBlockEnd helpers
- KeyboardShortcutsExtension: use selection helpers to account for
  suggestion nodes at block boundaries
- mergeBlocks: preserve suggestion nodes during block merging
- moveBlocks: PM-level move preserving internal node structure
- splitBlock: redirect splits inside suggestion nodes to blockContent
- nodeToBlock/prosemirrorSliceToSlicedBlocks: skip suggestion nodes
  when finding structural children
- createSpec: suggestion nodes now have parseHTML/renderHTML with
  data-suggestion attribute for HTML round-trip fidelity
- SpecialNode.test.ts: 20 tests covering structural, HTML parsing
  transparency, nodeToBlock, export, round-trip, DOMParser, and
  getBlockInfo interaction
- SpecialNodeOperations.test.ts: additional operation-level tests
- App.tsx example: multi-block demo with leading/trailing suggestions