--- a/src/Pure/Build/build.scala	Mon Jun 30 12:42:21 2025 +0200
+++ b/src/Pure/Build/build.scala	Mon Jun 30 13:10:44 2025 +0200
@@ -727,10 +727,6 @@
     yield {
       val thy_file = migrate_file(thy_file0)
 
-      val master_dir =
-        Path.explode(Url.strip_base_name(thy_file).getOrElse(
-          error("Cannot determine theory master directory: " + quote(thy_file))))
-
       val blobs =
         blobs_files0.map { name0 =>
           val name = migrate_file(name0)