diff --git a/docs/sql/2026-08-25-normalize-training-material-urls.sql b/docs/sql/2026-08-25-normalize-training-material-urls.sql
new file mode 100644
index 0000000..8eee737
--- /dev/null
+++ b/docs/sql/2026-08-25-normalize-training-material-urls.sql
@@ -0,0 +1,9 @@
+-- Case material links must be deployment-relative.  A persisted localhost URL
+-- makes a student's browser download from its own computer instead of this server.
+UPDATE training_task
+SET material_url = REGEXP_REPLACE(material_url, '^https?://(localhost|127\\.0\\.0\\.1)(:[0-9]+)?', '')
+WHERE material_url REGEXP '^https?://(localhost|127\\.0\\.0\\.1)(:[0-9]+)?/file/';
+
+UPDATE training_task_class_config
+SET material_url = REGEXP_REPLACE(material_url, '^https?://(localhost|127\\.0\\.0\\.1)(:[0-9]+)?', '')
+WHERE material_url REGEXP '^https?://(localhost|127\\.0\\.0\\.1)(:[0-9]+)?/file/';
diff --git a/src/main/resources/application-dev.yml b/src/main/resources/application-dev.yml
index 8b65284..75d87af 100644
--- a/src/main/resources/application-dev.yml
+++ b/src/main/resources/application-dev.yml
@@ -12,7 +12,9 @@ spring:
 file:
   type: local
   path: file
-  url: ${FILE_URL:http://localhost:7548/file}
+  # Keep public file URLs deployment-relative by default.  Absolute localhost URLs
+  # point to each student's own computer and cannot be used by other clients.
+  url: ${FILE_URL:/file}
   #path: D:/tianzeProject/linkCommerce/
   #url: "http://192.168.2.8:147/file"
 
@@ -27,4 +29,3 @@ item:
 
 
 
-