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+---
+id: task-027
+title: Implement proper Automerge CRDT sync for offline-first support
+status: In Progress
+assignee: []
+created_date: '2025-12-04 21:06'
+labels:
+  - offline-sync
+  - crdt
+  - automerge
+  - architecture
+dependencies: []
+priority: high
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Replace the current "last-write-wins" full document replacement with proper Automerge CRDT sync protocol. This ensures deletions are preserved across offline/reconnect scenarios and concurrent edits merge correctly.
+
+Current problem: Server does `currentDoc.store = { ...newDoc.store }` which is full replacement, not merge. This causes "ghost resurrection" of deleted shapes when offline clients reconnect.
+
+Solution: Use Automerge's native binary sync protocol with proper CRDT merge semantics.
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [ ] #1 Server stores Automerge binary documents in R2 (not JSON)
+- [ ] #2 Client-server communication uses Automerge sync protocol (binary messages)
+- [ ] #3 Deletions persist correctly when offline client reconnects
+- [ ] #4 Concurrent edits merge deterministically without data loss
+- [ ] #5 Existing JSON rooms are migrated to Automerge format
+- [ ] #6 All existing functionality continues to work
+<!-- AC:END -->