Avoid reinitializing virtual display

Author: hinerm

doc/llms/pyimagej-ai-guide.ipynb

@@ -373,27 +373,30 @@
     "# Install system dependencies only if needed\n",
     "!command -v mvn >/dev/null 2>&1 && command -v xdpyinfo >/dev/null 2>&1 || (apt-get update && apt-get install -y maven xvfb x11-utils libxext6 libxrender1 libxtst6 libxi6 fonts-dejavu)\n",
     "\n",
-    "# Start up a virtual display and test if it works\n",
-    "print(\"Setting up virtual display...\")\n",
-    "os.environ[\"DISPLAY\"] = \":99\"\n",
-    "xvfb_process = subprocess.Popen([\"Xvfb\", \":99\", \"-screen\", \"0\", \"1024x768x24\"])\n",
-    "\n",
-    "# Wait a moment for Xvfb to start\n",
-    "time.sleep(2)\n",
-    "\n",
-    "# Test if display is working\n",
-    "try:\n",
-    "    result = subprocess.run([\"xdpyinfo\"], capture_output=True, text=True, timeout=5)\n",
-    "    display_working = result.returncode == 0\n",
-    "    if display_working:\n",
-    "        print(\"✓ Virtual display working - using interactive mode\")\n",
-    "        ui_mode = 'interactive'\n",
-    "    else:\n",
-    "        print(\"⚠ Virtual display failed - falling back to headless mode\")\n",
+    "# Start up a virtual display only if needed\n",
+    "if \"DISPLAY\" not in os.environ:\n",
+    "    print(\"Setting up virtual display...\")\n",
+    "    os.environ[\"DISPLAY\"] = \":99\"\n",
+    "    xvfb_process = subprocess.Popen([\"Xvfb\", \":99\", \"-screen\", \"0\", \"1024x768x24\"])\n",
+    "\n",
+    "    # Wait a moment for Xvfb to start\n",
+    "    time.sleep(2)\n",
+    "\n",
+    "    # Test if display is working\n",
+    "    try:\n",
+    "        result = subprocess.run([\"xdpyinfo\"], capture_output=True, text=True, timeout=5)\n",
+    "        display_working = result.returncode == 0\n",
+    "        if display_working:\n",
+    "            print(\"✓ Virtual display working - using interactive mode\")\n",
+    "            ui_mode = 'interactive'\n",
+    "        else:\n",
+    "            print(\"⚠ Virtual display failed - falling back to headless mode\")\n",
+    "            ui_mode = 'headless'\n",
+    "    except (subprocess.TimeoutExpired, FileNotFoundError):\n",
+    "        print(\"⚠ Cannot test display - falling back to headless mode\")\n",
     "        ui_mode = 'headless'\n",
-    "except (subprocess.TimeoutExpired, FileNotFoundError):\n",
-    "    print(\"⚠ Cannot test display - falling back to headless mode\")\n",
-    "    ui_mode = 'headless'\n",
+    "else:\n",
+    "    print(f\"Display already configured: {os.environ['DISPLAY']}\")\n",
     "\n",
     "# Install PyImageJ if not already installed\n",
     "try:\n",