fix: incorrect inject field message for exact class extra field

Author: tomlau10

changelog.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 <!-- Add all new changes here. They will be moved under a version at release -->
+* `FIX` Incorrect inject-field message for extra table field in exact class
 
 ## 3.15.0
 `2025-6-25`

script/core/diagnostics/inject-field.lua

@@ -134,7 +134,7 @@ return function (uri, callback)
             end
             local message = lang.script('DIAG_INJECT_FIELD', {
                 class = vm.getInfer(src):view(uri),
-                field = guide.getKeyName(src),
+                field = guide.getKeyName(field),
                 fix   = '',
             })
             callback {