Automerge and Yjs CRDT architectures

Document status: reviewed. Canonical source.

Summary

Automerge provides Rust-backed CRDT data structures, compact change encoding and sync protocols for local-first applications. Yjs uses a modified YATA-style sequence CRDT with state-vector-based differential synchronization.

Executable NUIF boundary

nuif-collab-registers-0 exercises operation-set convergence without depending on either library. It compares pairwise-maximal and incremental-frontier materializers across every delivery order, keeps conflicts explicit and strips collaboration metadata from the checkpoint document. This is a profile-mechanism test, not evidence that Automerge and Yjs interoperate or make identical choices.

The follow-on nuif-collab-tree-0 uses the proved tree-move design and RGA-style stable sibling origins inside NUIF. Current Automerge Rust 0.11.0 and JavaScript 3.4.1 documentation still exposes maps, RGA lists, element cursors, change merging and synchronization but no tree-move operation. Its merge rules explicitly note that reverse list insertion does not always preserve insertion order. Gate H therefore pins JavaScript 3.4.1 only as a foreign transport oracle: seven replicas write immutable NUIF change records under distinct map keys, and forward, reverse, even/odd, duplicate and save/load merges must recover the exact record set. NUIF, not Automerge, materializes the tree and reports cycle/deletion conflicts. Sources: official merge rules https://automerge.org/docs/reference/under-the-hood/merge-rules/ and Rust 0.11.0 API https://docs.rs/automerge/0.11.0/automerge/ (retrieved 2026-08-30).

NUIF relevance

CRDTs are suitable for a collaboration profile and operation history, but their implementation-specific metadata should not become mandatory content of every canonical NUIF document. Saved documents must remain portable to non-collaborative implementations.