fix: only force-reconnect on tab visibility change, not on activity gaps

The 60s stale threshold was triggering during normal use (reading, thinking)
causing constant reconnects and presence join/leave toast spam. Now force-
reconnect only happens when the tab was hidden for 3+ minutes and becomes
visible again. Regular activity (mouse/keyboard) only resets the inactivity
timer without ever forcing a reconnect.

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

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

@@ -691,7 +691,7 @@ function FlowchartEditorInner({ projectId, projectName, userId, userDisplayName,
   useEffect(() => {
     const handleVisibilityChange = () => {
       if (!document.hidden) {
-        realtimeRef.current?.notifyActivity()
+        realtimeRef.current?.notifyVisibilityResumed()
       }
     }
 

src/lib/collaboration/realtime.ts

@@ -44,7 +44,7 @@ const RECONNECT_BASE_DELAY_MS = 1000
 const RECONNECT_MAX_DELAY_MS = 30_000
 const INACTIVITY_TIMEOUT_MS = 5 * 60_000 // 5 minutes of inactivity before pausing
 const CONNECTION_TIMEOUT_MS = 15_000 // 15s timeout for initial connection
-const STALE_THRESHOLD_MS = 60_000 // 60s of inactivity = force fresh reconnect on return
+const STALE_THRESHOLD_MS = 3 * 60_000 // 3 minutes hidden before forcing fresh reconnect
 
 export class RealtimeConnection {
   private channel: RealtimeChannel | null = null
@@ -77,6 +77,21 @@ export class RealtimeConnection {
     this.resetInactivityTimer()
     this.clearConnectionTimer()
 
+    // Ensure the Supabase client has a valid auth session before connecting.
+    // On initial page load, the session may still be loading from cookies.
+    try {
+      const { data: { session } } = await this.supabase.auth.getSession()
+      if (!session && !this.isDestroyed) {
+        // No session yet - wait briefly and retry
+        this.scheduleReconnect()
+        return
+      }
+    } catch {
+      // Session check failed - proceed anyway, channel will handle auth errors
+    }
+
+    if (this.isDestroyed || this.isPaused) return
+
     // Set a timeout: if we don't connect within CONNECTION_TIMEOUT_MS, retry
     this.connectionTimer = setTimeout(() => {
       if (this.isDestroyed || this.isPaused) return
@@ -247,21 +262,31 @@ export class RealtimeConnection {
   /**
    * Notify that user activity has occurred, resetting the inactivity timer.
    * If the connection was paused due to inactivity, it will resume.
-   * If the connection was idle for a significant period, force a fresh reconnect
-   * to ensure the WebSocket isn't stale.
    */
   notifyActivity(): void {
+    if (this.isDestroyed) return
+    this.lastActivityTime = Date.now()
+    this.resetInactivityTimer()
+
+    if (this.isPaused) {
+      this.resume()
+    }
+  }
+
+  /**
+   * Called when the tab becomes visible again. If the tab was hidden for a
+   * significant period, force a fresh reconnect to handle stale WebSockets.
+   */
+  notifyVisibilityResumed(): void {
     if (this.isDestroyed) return
     const now = Date.now()
-    const idleDuration = now - this.lastActivityTime
+    const hiddenDuration = now - this.lastActivityTime
     this.lastActivityTime = now
     this.resetInactivityTimer()
 
     if (this.isPaused) {
       this.resume()
-    } else if (idleDuration > STALE_THRESHOLD_MS && this.channel) {
-      // Connection may appear alive but WebSocket could be stale after idle.
-      // Force a fresh reconnect to ensure broadcasts actually work.
+    } else if (hiddenDuration > STALE_THRESHOLD_MS && this.channel) {
       this.forceReconnect()
     }
   }