src/app/editor/[projectId]/FlowchartEditor.tsx

@@ -527,6 +527,12 @@ function FlowchartEditorInner({ projectId, projectName, userId, userDisplayName,
 
   const [characters, setCharacters] = useState<Character[]>(migratedData.characters)
   const [variables, setVariables] = useState<Variable[]>(migratedData.variables)
+
+  // Refs to always have the latest characters/variables for the CRDT persist callback
+  const charactersRef = useRef(characters)
+  const variablesRef = useRef(variables)
+  charactersRef.current = characters
+  variablesRef.current = variables
   const [showSettings, setShowSettings] = useState(false)
   const [showShare, setShowShare] = useState(false)
   const [showHistory, setShowHistory] = useState(false)
@@ -540,7 +546,6 @@ function FlowchartEditorInner({ projectId, projectName, userId, userDisplayName,
   const realtimeRef = useRef<RealtimeConnection | null>(null)
   const crdtRef = useRef<CRDTManager | null>(null)
   const auditRef = useRef<AuditTrailRecorder | null>(null)
-  const isRemoteUpdateRef = useRef(false)
   const cursorThrottleRef = useRef<number>(0)
   const [collaborationNotifications, setCollaborationNotifications] = useState<CollaborationNotification[]>([])
   const [nodeLocks, setNodeLocks] = useState<Map<string, NodeLockInfo>>(new Map())
@@ -554,14 +559,10 @@ function FlowchartEditorInner({ projectId, projectName, userId, userDisplayName,
 
     const crdtManager = new CRDTManager({
       onNodesChange: (crdtNodes: FlowchartNode[]) => {
-        isRemoteUpdateRef.current = true
         setNodes(toReactFlowNodes(crdtNodes))
-        isRemoteUpdateRef.current = false
       },
       onEdgesChange: (crdtEdges: FlowchartEdge[]) => {
-        isRemoteUpdateRef.current = true
         setEdges(toReactFlowEdges(crdtEdges))
-        isRemoteUpdateRef.current = false
       },
       onPersist: async (persistNodes: FlowchartNode[], persistEdges: FlowchartEdge[]) => {
         try {
@@ -571,8 +572,8 @@ function FlowchartEditorInner({ projectId, projectName, userId, userDisplayName,
               flowchart_data: {
                 nodes: persistNodes,
                 edges: persistEdges,
-                characters,
-                variables,
+                characters: charactersRef.current,
+                variables: variablesRef.current,
               },
             })
             .eq('id', projectId)
@@ -633,6 +634,9 @@ function FlowchartEditorInner({ projectId, projectName, userId, userDisplayName,
           return next
         })
       },
+      onCRDTUpdate: (update: number[]) => {
+        crdtManager.applyRemoteUpdate(update)
+      },
       onChannelSubscribed: (channel) => {
         crdtManager.connectChannel(channel)
       },
@@ -678,7 +682,6 @@ function FlowchartEditorInner({ projectId, projectName, userId, userDisplayName,
   }, [edges])
 
   useEffect(() => {
-    if (isRemoteUpdateRef.current) return
     crdtRef.current?.updateNodes(nodesForCRDT)
     if (!isRevertingRef.current) {
       auditRef.current?.recordNodeChanges(nodesForCRDT)
@@ -686,7 +689,6 @@ function FlowchartEditorInner({ projectId, projectName, userId, userDisplayName,
   }, [nodesForCRDT])
 
   useEffect(() => {
-    if (isRemoteUpdateRef.current) return
     crdtRef.current?.updateEdges(edgesForCRDT)
     if (!isRevertingRef.current) {
       auditRef.current?.recordEdgeChanges(edgesForCRDT)

src/lib/collaboration/crdt.ts

@@ -57,25 +57,23 @@ export class CRDTManager {
     }, 'init')
   }
 
-  /** Connect to a Supabase Realtime channel for syncing updates */
+  /** Connect to a Supabase Realtime channel for outbound broadcasts */
   connectChannel(channel: RealtimeChannel): void {
     this.channel = channel
+  }
 
-    // Listen for broadcast updates from other clients
-    channel.on('broadcast', { event: BROADCAST_EVENT }, (payload) => {
+  /** Apply a remote CRDT update received via broadcast */
+  applyRemoteUpdate(updateData: number[]): void {
     if (this.isDestroyed) return
-      const data = payload.payload as { update?: number[] } | undefined
-      if (data?.update) {
-        const update = new Uint8Array(data.update)
+    const update = new Uint8Array(updateData)
     this.isApplyingRemote = true
     Y.applyUpdate(this.doc, update, 'remote')
     this.isApplyingRemote = false
     // Notify React state of remote changes
     this.notifyNodesChange()
     this.notifyEdgesChange()
-        this.schedulePersist()
-      }
-    })
+    // Note: we do NOT schedulePersist here. Only the originating client
+    // persists its own changes to avoid write races and stale data overwrites.
   }
 
   /** Apply local node changes to the Yjs document */

src/lib/collaboration/realtime.ts

@@ -35,6 +35,7 @@ type RealtimeCallbacks = {
   onChannelSubscribed?: (channel: RealtimeChannel) => void
   onCursorUpdate?: (cursor: RemoteCursor) => void
   onNodeLockUpdate?: (lock: NodeLock | null, userId: string) => void
+  onCRDTUpdate?: (update: number[]) => void
 }
 
 const HEARTBEAT_INTERVAL_MS = 30_000
@@ -131,6 +132,11 @@ export class RealtimeConnection {
           this.callbacks.onNodeLockUpdate?.(null, payload.userId)
         }
       })
+      .on('broadcast', { event: 'yjs-update' }, ({ payload }) => {
+        if (payload?.update) {
+          this.callbacks.onCRDTUpdate?.(payload.update)
+        }
+      })
       .subscribe(async (status) => {
         if (this.isDestroyed) return