feat: notify collaborators to refresh from DB after save

Instead of relying on Yjs broadcast serialization (which has delivery
issues), use a lightweight state-refresh broadcast event. When any
client persists (manual save or CRDT auto-persist), it broadcasts
state-refresh. Other clients fetch the latest flowchart_data from the
database and update their local state and CRDT.

Added isSuppressed flag to CRDTManager to prevent broadcast/persist
loops during initialization and refresh operations.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/lib/collaboration/crdt.ts

@@ -19,6 +19,7 @@ export class CRDTManager {
   private callbacks: CRDTCallbacks
   private persistTimer: ReturnType<typeof setTimeout> | null = null
   private isApplyingRemote = false
+  private isSuppressed = false // suppress broadcast/persist during init or refresh
   private isDestroyed = false
 
   constructor(callbacks: CRDTCallbacks) {
@@ -29,24 +30,25 @@ export class CRDTManager {
 
     // Schedule persistence on local Yjs document changes
     this.nodesMap.observe(() => {
-      if (this.isApplyingRemote) return
+      if (this.isApplyingRemote || this.isSuppressed) return
       this.schedulePersist()
     })
 
     this.edgesMap.observe(() => {
-      if (this.isApplyingRemote) return
+      if (this.isApplyingRemote || this.isSuppressed) return
       this.schedulePersist()
     })
 
     // Broadcast local updates to other clients
     this.doc.on('update', (update: Uint8Array, origin: unknown) => {
-      if (origin === 'remote') return // Don't re-broadcast remote updates
+      if (origin === 'remote' || this.isSuppressed) return
       this.broadcastUpdate(update)
     })
   }
 
   /** Initialize the Yjs document from database state */
   initializeFromData(nodes: FlowchartNode[], edges: FlowchartEdge[]): void {
+    this.isSuppressed = true
     this.doc.transact(() => {
       nodes.forEach((node) => {
         this.nodesMap.set(node.id, JSON.stringify(node))
@@ -55,6 +57,7 @@ export class CRDTManager {
         this.edgesMap.set(edge.id, JSON.stringify(edge))
       })
     }, 'init')
+    this.isSuppressed = false
   }
 
   /** Connect to a Supabase Realtime channel for outbound broadcasts */
@@ -76,6 +79,37 @@ export class CRDTManager {
     // persists its own changes to avoid write races and stale data overwrites.
   }
 
+  /** Replace CRDT state from a database refresh without broadcasting */
+  refreshFromData(nodes: FlowchartNode[], edges: FlowchartEdge[]): void {
+    this.isSuppressed = true
+    this.doc.transact(() => {
+      // Sync nodes
+      const nodeIds = new Set(nodes.map((n) => n.id))
+      Array.from(this.nodesMap.keys()).forEach((id) => {
+        if (!nodeIds.has(id)) this.nodesMap.delete(id)
+      })
+      nodes.forEach((node) => {
+        const serialized = JSON.stringify(node)
+        if (this.nodesMap.get(node.id) !== serialized) {
+          this.nodesMap.set(node.id, serialized)
+        }
+      })
+
+      // Sync edges
+      const edgeIds = new Set(edges.map((e) => e.id))
+      Array.from(this.edgesMap.keys()).forEach((id) => {
+        if (!edgeIds.has(id)) this.edgesMap.delete(id)
+      })
+      edges.forEach((edge) => {
+        const serialized = JSON.stringify(edge)
+        if (this.edgesMap.get(edge.id) !== serialized) {
+          this.edgesMap.set(edge.id, serialized)
+        }
+      })
+    }, 'remote')
+    this.isSuppressed = false
+  }
+
   /** Apply local node changes to the Yjs document */
   updateNodes(nodes: FlowchartNode[]): void {
     if (this.isApplyingRemote) return
@@ -173,17 +207,6 @@ export class CRDTManager {
     this.callbacks.onEdgesChange(this.getEdges())
   }
 
-  /** Broadcast the full document state to sync all connected clients */
-  broadcastFullState(): void {
-    if (!this.channel || this.isDestroyed) return
-    const fullState = Y.encodeStateAsUpdate(this.doc)
-    this.channel.send({
-      type: 'broadcast',
-      event: BROADCAST_EVENT,
-      payload: { update: Array.from(fullState) },
-    })
-  }
-
   private broadcastUpdate(update: Uint8Array): void {
     if (!this.channel || this.isDestroyed) return
     this.channel.send({

src/lib/collaboration/realtime.ts

@@ -36,6 +36,7 @@ type RealtimeCallbacks = {
   onCursorUpdate?: (cursor: RemoteCursor) => void
   onNodeLockUpdate?: (lock: NodeLock | null, userId: string) => void
   onCRDTUpdate?: (update: number[]) => void
+  onStateRefresh?: () => void
 }
 
 const HEARTBEAT_INTERVAL_MS = 30_000
@@ -137,6 +138,9 @@ export class RealtimeConnection {
           this.callbacks.onCRDTUpdate?.(payload.update)
         }
       })
+      .on('broadcast', { event: 'state-refresh' }, () => {
+        this.callbacks.onStateRefresh?.()
+      })
       .subscribe(async (status) => {
         if (this.isDestroyed) return
 
@@ -195,6 +199,15 @@ export class RealtimeConnection {
     })
   }
 
+  broadcastStateRefresh(): void {
+    if (!this.channel) return
+    this.channel.send({
+      type: 'broadcast',
+      event: 'state-refresh',
+      payload: {},
+    })
+  }
+
   broadcastNodeLock(nodeId: string | null): void {
     if (!this.channel) return
     this.channel.send({