automerge-sync

name	automerge-sync
description	Reference for Automerge 0.5 CRDT sync engine, stream positions, delta sync protocol, document lifecycle, conflict resolution, and browser-side integration. Use when someone asks "how does sync work", "handle merge conflicts", "manage stream positions", "offline-first content", or implements CRDT document flows.
metadata	{"runtime":"codex","sourceRuntime":"claude","master":"package","sourcePath":".epr-meta/elohim/packages/skills/automerge-sync.json","packageKind":"SkillPackage"}
governance	epr:elohim-agent/skills/automerge-sync

Automerge Sync Engine Reference

The sync engine provides local-first experience with CRDT-based conflict resolution using Automerge.

Design Philosophy

• Offline-first: Full functionality without network
• Eventual consistency: All nodes converge to same state
• No conflicts: CRDTs make concurrent edits merge cleanly
• Stream-based sync: Delta updates via position tracking

---

Document Model

Each content item is one Automerge document, stored in SQLite (native) or IndexedDB (browser).

Content item "concept-governance"  ->  Automerge document (binary blob)
Content item "path-onboarding"     ->  Automerge document (binary blob)
User progress "user123/concept-x"  ->  Automerge document (binary blob)

What goes in Automerge docs:

• Content metadata (title, description, type)
• Path definitions (chapters, steps, ordering)
• User progress (mastery levels, engagement counts)

What does NOT go in Automerge docs:

• Media files (use blob/shard storage instead - hash references only)
• Attestations (use Holochain DHT)
• Trust links (use Holochain DHT)

---

Stream Positions

Inspired by Matrix's sync API. Each agent maintains a monotonic sequence number.

pub struct AgentStream {
    /// Current position (monotonically increasing)
    pub position: u64,

    /// Recent events for quick replay
    pub recent_events: VecDeque<SyncEvent>,

    /// Maximum events to keep in memory
    pub max_recent: usize,
}

SyncEvent

pub struct SyncEvent {
    /// Position in this agent's stream
    pub position: u64,

    /// Document that changed
    pub doc_id: String,

    /// Automerge change hash
    pub change_hash: String,

    /// Kind of event
    pub kind: EventKind,

    /// Timestamp
    pub timestamp: u64,
}

Event Kinds

pub enum EventKind {
    Local,      // I created this change locally
    New,        // Just received from a peer
    Backfill,   // Historical sync (catching up)
    Outlier,    // Received reference before content (DAG gap)
}

Kind	When Used	Priority
Local	User edits offline	Highest - sync first
New	Received from peer	High - recent activity
Backfill	Joining network	Normal - historical
Outlier	DAG incomplete	Low - resolve later

---

Sync Protocol

Message Types

pub enum SyncMessage {
    /// Request events since position
    SyncRequest {
        since: u64,
        limit: Option<u32>,
    },

    /// Response with events
    SyncResponse {
        events: Vec<SyncEvent>,
        has_more: bool,
    },

    /// Request document changes
    DocRequest {
        doc_id: String,
        heads: Vec<String>,  // Automerge heads we have
    },

    /// Response with document changes
    DocResponse {
        doc_id: String,
        changes: Vec<Vec<u8>>,  // Automerge change blobs
    },

    /// Announce new local event
    Announce {
        event: SyncEvent,
    },
}

Sync Flow

Node A (position: 100)              Node B (position: 85)

1. Connect                          1. Connect

2. Exchange positions               2. Exchange positions
   "I'm at 100"  ───────────────>
                  <───────────────  "I'm at 85"

3. B is behind, A sends             3. Receive events 86-100
   events 86-100  ───────────────>

                                    4. For each new doc_id:
                                       DocRequest { doc_id, heads }
                  <───────────────

5. DocResponse { changes }          5. Merge changes into local doc
               ───────────────>

6. Both at 100                      6. Now at 100

Periodic Sync

The SyncCoordinator schedules periodic sync with connected peers:

Every 30s:
  For each connected peer:
    If peer.sync_position < my_position:
      Send SyncResponse with delta events
    If peer.sync_position > my_position:
      Send SyncRequest { since: my_position }

---

Conflict Resolution

Automerge handles conflicts automatically:

Different fields - Both changes preserved:

Initial: { title: "Original", version: 1 }
Alice:   { title: "Alice's Title", version: 1 }
Bob:     { title: "Original", version: 2 }
Merged:  { title: "Alice's Title", version: 2 }

Same field - Deterministic winner (by actor ID):

Initial: { status: "draft" }
Alice:   { status: "published" }
Bob:     { status: "archived" }
Merged:  { status: "published" }  // if Alice's ID < Bob's

Access conflicting values:

doc.get_conflicts("status")  // ["published", "archived"]

Governance Override

For conflicts requiring human judgment:

pub enum ConflictResolution {
    Automatic(AutomergeResolution),
    Governance {
        conflict_id: String,
        options: Vec<ConflictOption>,
    },
}

---

Document Lifecycle

Creating: build Automerge doc -> store locally -> add to event log (EventKind::Local) -> announce to peers. Receiving: check if doc exists -> full request (empty heads) or incremental sync (send our heads) -> merge -> log as EventKind::New.

See references/document-lifecycle.md for full Rust code examples, SQLite/IndexedDB schemas, storage-client-ts sync methods, and OfflineOperationQueueService patterns.

storage-client-ts Sync Methods

Key methods: listDocuments(), getHeads(), getChangesSince(), applyChanges(), countDocuments(). See references/document-lifecycle.md for usage examples.

---

Gotchas

1. Automerge 0.5 crate vs 3.0 design - The Rust crate is automerge = "0.5" (in Cargo.toml). The design docs reference "Automerge 3.0" which is the JavaScript version. The Rust API differs.

2. Per-agent stream positions - Each agent has its own monotonic position. Don't confuse with document-level heads. Positions track the agent's event log, heads track document state.

3. DAG gaps (Outlier events) - If you receive a change reference before having the change itself, mark as Outlier and fetch later. Don't block sync.

4. Blob references, not blob sync - Automerge docs contain hash references to blobs. The blob data itself transfers via the shard protocol, not the sync protocol.

5. CRDT merge is deterministic - Same inputs always produce same output. No coordination needed for merge. But same-field conflicts resolve by actor ID ordering, which may surprise users.

---

Key Files

File	Purpose
elohim/holochain/docs/SYNC-ENGINE.md	Primary design document
steward/node/src/sync/coordinator.rs	SyncCoordinator (peer tracking, scheduling)
steward/node/src/sync/protocol.rs	SyncMessage types
steward/node/src/sync/stream.rs	AgentStream, position tracking
steward/node/src/sync/merge.rs	Automerge merge operations
elohim/sdk/storage-client-ts/src/client.ts	TypeScript sync API
elohim/holochain/docs/P2P-DATAPLANE.md	Overall P2P architecture

External References

• Automerge docs: https://automerge.org/docs/
• Automerge Rust crate (0.5): https://docs.rs/automerge/0.5/automerge/
• Automerge JS: https://automerge.org/docs/quickstart/