diff --git a/backend/Dockerfile b/backend/Dockerfile
index 4d9e9907..a2ba69c8 100644
--- a/backend/Dockerfile
+++ b/backend/Dockerfile
@@ -1,3 +1,7 @@
+# [D-07] Backend container - config/ folder mounted at /app/config (read-only)
+# Config sources: /app/config/backend.yaml, /app/config/secrets.yaml, environment variables
+# Environment variables override YAML config per D-06 load order
+
 FROM python:3.12-slim
 
 # Metadata labels