feat(perf): Implement performance threshold alert system

gui.py

@@ -502,6 +502,7 @@ class App:
         ai_client.comms_log_callback = self._on_comms_entry
         ai_client.tool_log_callback = self._on_tool_log
         mcp_client.perf_monitor_callback = self.perf_monitor.get_metrics
+        self.perf_monitor.alert_callback = self._on_performance_alert
 
     # ---------------------------------------------------------------- project loading
 
@@ -755,6 +756,17 @@ class App:
         """Called from background thread when a tool call completes."""
         session_logger.log_tool_call(script, result, None)
 
+    def _on_performance_alert(self, message: str):
+        """Called by PerformanceMonitor when a threshold is exceeded."""
+        alert_text = f"[PERFORMANCE ALERT] {message}. Please consider optimizing recent changes or reducing load."
+        # Inject into history as a 'System' message or similar
+        with self._pending_history_adds_lock:
+            self._pending_history_adds.append({
+                "role": "System",
+                "content": alert_text,
+                "ts": project_manager.now_ts()
+            })
+
     def _flush_pending_comms(self):
         """Called every frame from the main render loop."""
         with self._pending_comms_lock: