diff --git a/.env b/.env
index 5fe6fc9..ed8fed3 100644
--- a/.env
+++ b/.env
@@ -1 +1,15 @@
+# The Lucia project.
+# Copyright 2023-2026 DSP, inc.  All rights reserved.
+# Authors:
+#   chiayin.kuo@dsp.im (chiayin), 2023/1/31
+#   imacat.yang@dsp.im (imacat), 2026/3/6
+#
+# Default environment variables.
+# Override in .env.local for local development.
+
+# Backend API URL for the dev server proxy.
 VUE_APP_API_URL = ""
+
+# Custom Vite cache directory (default: node_modules/.vite).
+# Set to /tmp/vite-cache for systemd deployment with PrivateTmp.
+VITE_CACHE_DIR = ""