feat: Engram sync layer — swarm memory protocol, peer delta sync, distributed activation

engram/crates/engram-core/src/db.rs

@@ -187,6 +187,34 @@ mod sled_impl {
         pub fn edge_count(&self) -> EngramResult<usize> {
             graph::edge_count(&self.db)
         }
+
+        // ── Bulk scan (for sync) ───────────────────────────────────────────────
+
+        /// Scan all nodes in the store.
+        ///
+        /// Used by the sync engine to generate delta snapshots.
+        pub fn scan_nodes(&self) -> EngramResult<Vec<crate::types::Node>> {
+            storage::scan_nodes(&self.db)
+        }
+
+        /// Scan all edges in the store (forward index only).
+        pub fn scan_edges(&self) -> EngramResult<Vec<Edge>> {
+            let prefix = b"edges:from:";
+            let mut edges = Vec::new();
+            for result in self.db.scan_prefix(prefix) {
+                let (_k, v) = result?;
+                let edge: Edge = bincode::deserialize(&v)?;
+                edges.push(edge);
+            }
+            Ok(edges)
+        }
+
+        /// Delete a node by UUID (tombstone support for sync).
+        pub fn delete_node(&self, id: Uuid) -> EngramResult<()> {
+            let key = storage::node_key(id);
+            self.db.remove(key)?;
+            Ok(())
+        }
     }
 }