diff --git a/src/AcDream.Platform/ApplicationPathSet.cs b/src/AcDream.Platform/ApplicationPathSet.cs
index a6743ad1..76e3a1f5 100644
--- a/src/AcDream.Platform/ApplicationPathSet.cs
+++ b/src/AcDream.Platform/ApplicationPathSet.cs
@@ -72,6 +72,16 @@ public sealed record ApplicationPathSet(
     {
         platform ??= ApplicationPathEnvironment.Instance;
 
+        // Explicit method/CLI arguments remain authoritative. The environment
+        // seam lets graphical automation and portable installations isolate
+        // all mutable user state without rewriting the real user's settings.
+        configDirectory ??= NonEmpty(
+            platform.GetEnvironmentVariable("ACDREAM_CONFIG_DIR"));
+        dataDirectory ??= NonEmpty(
+            platform.GetEnvironmentVariable("ACDREAM_DATA_DIR"));
+        cacheDirectory ??= NonEmpty(
+            platform.GetEnvironmentVariable("ACDREAM_CACHE_DIR"));
+
         string config;
         string data;
         string cache;
@@ -140,6 +150,9 @@ public sealed record ApplicationPathSet(
         return Path.Combine(root, leaf);
     }
 
+    private static string? NonEmpty(string? value) =>
+        string.IsNullOrWhiteSpace(value) ? null : value;
+
     private static string RequireFolder(
         IApplicationPathEnvironment platform,
         Environment.SpecialFolder folder)