diff --git a/backend/lib/cgc_2046/courses/course.ex b/backend/lib/cgc_2046/courses/course.ex
index 6417d22b..fe0fb25f 100644
--- a/backend/lib/cgc_2046/courses/course.ex
+++ b/backend/lib/cgc_2046/courses/course.ex
@@ -428,6 +428,9 @@ defmodule Cgc2046.Courses.Course do
           Ash.Changeset.add_error(
             changeset,
             field: :slug,
+            # 带被拒新值——Ash keyword add_error 不传 :value 时错误消息 Value 恒为 nil,
+            # 排障时无法区分「参数丢失」与「锁定拦截」(2026-09-09 生产实例误判过)
+            value: Ash.Changeset.get_attribute(changeset, :slug),
             message: "slug is locked once the offering is published (editable in draft only)"
           )
         else
diff --git a/backend/lib/cgc_2046/events/event.ex b/backend/lib/cgc_2046/events/event.ex
index 989736d2..f94bc6ff 100644
--- a/backend/lib/cgc_2046/events/event.ex
+++ b/backend/lib/cgc_2046/events/event.ex
@@ -430,6 +430,9 @@ defmodule Cgc2046.Events.Event do
           Ash.Changeset.add_error(
             changeset,
             field: :slug,
+            # 带被拒新值——Ash keyword add_error 不传 :value 时错误消息 Value 恒为 nil,
+            # 排障时无法区分「参数丢失」与「锁定拦截」(2026-09-09 生产实例误判过)
+            value: Ash.Changeset.get_attribute(changeset, :slug),
             message: "slug is locked once the offering is published (editable in draft only)"
           )
         else
diff --git a/backend/test/cgc_2046/events/event_slug_test.exs b/backend/test/cgc_2046/events/event_slug_test.exs
index 5920ba48..81380465 100644
--- a/backend/test/cgc_2046/events/event_slug_test.exs
+++ b/backend/test/cgc_2046/events/event_slug_test.exs
@@ -171,6 +171,9 @@ defmodule Cgc2046.Events.EventSlugTest do
 
     assert Exception.message(error) =~ "slug is locked"
 
+    # 错误须带被拒新值(可观测性:区分「参数丢失」与「锁定拦截」,2026-09-09 生产误判)
+    assert Exception.message(error) =~ ~s(Value: "new-slug")
+
     assert Ash.get!(Event, event.id, tenant: workspace.id, authorize?: false).slug ==
              "lock-open-event"
   end