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

@@ -27,13 +27,14 @@ import ConditionEditor from '@/components/editor/ConditionEditor'
 import ExportValidationModal, { type ValidationIssue } from '@/components/editor/ExportValidationModal'
 import { EditorProvider } from '@/components/editor/EditorContext'
 import Toast from '@/components/Toast'
-import { RealtimeConnection, type ConnectionState } from '@/lib/collaboration/realtime'
+import { RealtimeConnection, type ConnectionState, type PresenceUser } from '@/lib/collaboration/realtime'
 import ShareModal from '@/components/editor/ShareModal'
 import type { FlowchartData, FlowchartNode, FlowchartEdge, Character, Variable, Condition } from '@/types/flowchart'
 
 type FlowchartEditorProps = {
   projectId: string
   userId: string
+  userDisplayName: string
   isOwner: boolean
   initialData: FlowchartData
   needsMigration?: boolean
@@ -206,7 +207,7 @@ function computeMigration(initialData: FlowchartData, shouldMigrate: boolean) {
 }
 
 // Inner component that uses useReactFlow hook
-function FlowchartEditorInner({ projectId, userId, isOwner, initialData, needsMigration }: FlowchartEditorProps) {
+function FlowchartEditorInner({ projectId, userId, userDisplayName, isOwner, initialData, needsMigration }: FlowchartEditorProps) {
   // Define custom node types - memoized to prevent re-renders
   const nodeTypes: NodeTypes = useMemo(
     () => ({
@@ -238,12 +239,14 @@ function FlowchartEditorInner({ projectId, userId, isOwner, initialData, needsMi
   const [validationIssues, setValidationIssues] = useState<ValidationIssue[] | null>(null)
   const [warningNodeIds, setWarningNodeIds] = useState<Set<string>>(new Set())
   const [connectionState, setConnectionState] = useState<ConnectionState>('disconnected')
+  const [presenceUsers, setPresenceUsers] = useState<PresenceUser[]>([])
   const realtimeRef = useRef<RealtimeConnection | null>(null)
 
   // Connect to Supabase Realtime channel on mount, disconnect on unmount
   useEffect(() => {
-    const connection = new RealtimeConnection(projectId, userId, {
+    const connection = new RealtimeConnection(projectId, userId, userDisplayName, {
       onConnectionStateChange: setConnectionState,
+      onPresenceSync: setPresenceUsers,
     })
     realtimeRef.current = connection
     connection.connect()
@@ -252,7 +255,7 @@ function FlowchartEditorInner({ projectId, userId, isOwner, initialData, needsMi
       connection.disconnect()
       realtimeRef.current = null
     }
-  }, [projectId, userId])
+  }, [projectId, userId, userDisplayName])
 
   const handleAddCharacter = useCallback(
     (name: string, color: string): string => {
@@ -534,6 +537,7 @@ function FlowchartEditorInner({ projectId, userId, isOwner, initialData, needsMi
           onProjectSettings={() => setShowSettings(true)}
           onShare={() => setShowShare(true)}
           connectionState={connectionState}
+          presenceUsers={presenceUsers}
         />
         <div className="flex-1">
           <ReactFlow

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

@@ -20,6 +20,15 @@ export default async function EditorPage({ params }: PageProps) {
     return null
   }
 
+  // Fetch user's display name for presence
+  const { data: profile } = await supabase
+    .from('profiles')
+    .select('display_name')
+    .eq('id', user.id)
+    .single()
+
+  const userDisplayName = profile?.display_name || user.email || 'Anonymous'
+
   // Try to load as owner first
   const { data: ownedProject } = await supabase
     .from('projects')
@@ -102,6 +111,7 @@ export default async function EditorPage({ params }: PageProps) {
         <FlowchartEditor
           projectId={project.id}
           userId={user.id}
+          userDisplayName={userDisplayName}
           isOwner={isOwner}
           initialData={flowchartData}
           needsMigration={needsMigration}

src/components/editor/PresenceAvatars.tsx

@@ -0,0 +1,65 @@
+'use client'
+
+import type { PresenceUser } from '@/lib/collaboration/realtime'
+
+type PresenceAvatarsProps = {
+  users: PresenceUser[]
+}
+
+const MAX_VISIBLE = 5
+
+// Generate a consistent color from a user ID hash
+function getUserColor(userId: string): string {
+  let hash = 0
+  for (let i = 0; i < userId.length; i++) {
+    hash = ((hash << 5) - hash + userId.charCodeAt(i)) | 0
+  }
+  const colors = [
+    '#EF4444', '#F97316', '#F59E0B', '#10B981',
+    '#3B82F6', '#8B5CF6', '#EC4899', '#14B8A6',
+    '#6366F1', '#F43F5E', '#84CC16', '#06B6D4',
+  ]
+  return colors[Math.abs(hash) % colors.length]
+}
+
+// Get initials from a display name (first letter of first two words)
+function getInitials(displayName: string): string {
+  const parts = displayName.trim().split(/\s+/)
+  if (parts.length >= 2) {
+    return (parts[0][0] + parts[1][0]).toUpperCase()
+  }
+  return displayName.slice(0, 2).toUpperCase()
+}
+
+export default function PresenceAvatars({ users }: PresenceAvatarsProps) {
+  if (users.length === 0) return null
+
+  const visibleUsers = users.slice(0, MAX_VISIBLE)
+  const overflow = users.length - MAX_VISIBLE
+
+  return (
+    <div className="flex items-center -space-x-2">
+      {visibleUsers.map((user) => {
+        const color = getUserColor(user.userId)
+        return (
+          <div
+            key={user.userId}
+            title={user.displayName}
+            className="relative flex h-7 w-7 items-center justify-center rounded-full border-2 border-white text-[10px] font-semibold text-white dark:border-zinc-800"
+            style={{ backgroundColor: color }}
+          >
+            {getInitials(user.displayName)}
+          </div>
+        )
+      })}
+      {overflow > 0 && (
+        <div
+          className="relative flex h-7 w-7 items-center justify-center rounded-full border-2 border-white bg-zinc-400 text-[10px] font-semibold text-white dark:border-zinc-800 dark:bg-zinc-500"
+          title={`${overflow} more collaborator${overflow > 1 ? 's' : ''}`}
+        >
+          +{overflow}
+        </div>
+      )}
+    </div>
+  )
+}

src/components/editor/Toolbar.tsx

@@ -1,6 +1,7 @@
 'use client'
 
-import type { ConnectionState } from '@/lib/collaboration/realtime'
+import type { ConnectionState, PresenceUser } from '@/lib/collaboration/realtime'
+import PresenceAvatars from './PresenceAvatars'
 
 type ToolbarProps = {
   onAddDialogue: () => void
@@ -12,6 +13,7 @@ type ToolbarProps = {
   onProjectSettings: () => void
   onShare: () => void
   connectionState?: ConnectionState
+  presenceUsers?: PresenceUser[]
 }
 
 const connectionLabel: Record<ConnectionState, string> = {
@@ -38,6 +40,7 @@ export default function Toolbar({
   onProjectSettings,
   onShare,
   connectionState,
+  presenceUsers,
 }: ToolbarProps) {
   return (
     <div className="flex items-center justify-between border-b border-zinc-200 bg-zinc-50 px-4 py-2 dark:border-zinc-700 dark:bg-zinc-800">
@@ -66,6 +69,11 @@ export default function Toolbar({
       </div>
 
       <div className="flex items-center gap-2">
+        {presenceUsers && presenceUsers.length > 0 && (
+          <div className="mr-2">
+            <PresenceAvatars users={presenceUsers} />
+          </div>
+        )}
         {connectionState && (
           <div className="flex items-center gap-1.5 mr-2" title={connectionLabel[connectionState]}>
             <span className={`inline-block h-2.5 w-2.5 rounded-full ${connectionColor[connectionState]}${connectionState === 'reconnecting' ? ' animate-pulse' : ''}`} />

src/lib/collaboration/realtime.ts

@@ -3,9 +3,14 @@ import type { RealtimeChannel } from '@supabase/supabase-js'
 
 export type ConnectionState = 'connecting' | 'connected' | 'disconnected' | 'reconnecting'
 
+export type PresenceUser = {
+  userId: string
+  displayName: string
+}
+
 type RealtimeCallbacks = {
   onConnectionStateChange: (state: ConnectionState) => void
-  onPresenceSync?: (presences: Record<string, unknown[]>) => void
+  onPresenceSync?: (users: PresenceUser[]) => void
 }
 
 const HEARTBEAT_INTERVAL_MS = 30_000
@@ -19,13 +24,15 @@ export class RealtimeConnection {
   private reconnectAttempts = 0
   private projectId: string
   private userId: string
+  private displayName: string
   private callbacks: RealtimeCallbacks
   private isDestroyed = false
   private supabase = createClient()
 
-  constructor(projectId: string, userId: string, callbacks: RealtimeCallbacks) {
+  constructor(projectId: string, userId: string, displayName: string, callbacks: RealtimeCallbacks) {
     this.projectId = projectId
     this.userId = userId
+    this.displayName = displayName
     this.callbacks = callbacks
   }
 
@@ -41,7 +48,18 @@ export class RealtimeConnection {
       .on('presence', { event: 'sync' }, () => {
         if (this.channel) {
           const state = this.channel.presenceState()
-          this.callbacks.onPresenceSync?.(state)
+          const users: PresenceUser[] = []
+          for (const [key, presences] of Object.entries(state)) {
+            if (key === this.userId) continue // Exclude own presence
+            const presence = presences[0] as { userId?: string; displayName?: string } | undefined
+            if (presence?.userId) {
+              users.push({
+                userId: presence.userId,
+                displayName: presence.displayName || 'Anonymous',
+              })
+            }
+          }
+          this.callbacks.onPresenceSync?.(users)
         }
       })
       .subscribe(async (status) => {
@@ -52,6 +70,11 @@ export class RealtimeConnection {
           this.callbacks.onConnectionStateChange('connected')
           this.startHeartbeat()
           await this.createSession()
+          // Track presence with user info
+          await this.channel?.track({
+            userId: this.userId,
+            displayName: this.displayName,
+          })
         } else if (status === 'CHANNEL_ERROR' || status === 'TIMED_OUT') {
           this.callbacks.onConnectionStateChange('reconnecting')
           this.scheduleReconnect()