fix: restore brainstorming feature with missing socket server and real-time events

memento-note/app/api/brainstorm/[sessionId]/expand/route.ts

@@ -15,7 +15,9 @@ import {
   resolveAiContextUserId,
   sanitizeNotesForGuest,
   captureSnapshot,
+  logActivity,
 } from '@/lib/brainstorm-collab'
+import { emitToSession } from '@/lib/socket-emit'
 
 const expandSchema = z.object({
   ideaId: z.string().min(1),
@@ -332,6 +334,17 @@ export async function POST(
       for (const idea of updatedSession?.ideas || []) { (idea as any).creator = (idea as any).createdBy ? cm.get((idea as any).createdBy) || null : null }
     }
 
+    await logActivity(sessionId, 'wave_generated', session.user.id, { count: newIdeas.length, parentIdeaId: ideaId })
+
+    await emitToSession(sessionId, 'activity:new', {
+      action: 'wave_generated',
+      userId: session.user.id,
+      userName: session.user.name || 'Guest',
+      details: { count: newIdeas.length, parentIdeaId: ideaId }
+    })
+    // Trigger refetch for all participants
+    await emitToSession(sessionId, 'idea:added', {})
+
     await captureSnapshot(sessionId, `Wave expanded: ${parentIdea.title}`).catch(() => {})
 
     return NextResponse.json({ success: true, data: updatedSession })