back to xz-java-1.9, to see if this improves build_manager stability;
enforce rebuild of Isabelle/ML and Isabelle/Scala, in a robust manner using random UUID;

--- a/Admin/components/main	Thu Dec 19 17:01:54 2024 +0000
+++ b/Admin/components/main	Thu Dec 19 22:19:27 2024 +0100
@@ -39,7 +39,7 @@
 verit-2021.06.2-rmx-1
 vscode_extension-20241002
 vscodium-1.70.1
-xz-java-1.10
+xz-java-1.9
 z3-4.4.0pre-4
 zipperposition-2.1-1
 zstd-jni-1.5.6-8

--- a/src/Pure/ROOT.ML	Thu Dec 19 17:01:54 2024 +0000
+++ b/src/Pure/ROOT.ML	Thu Dec 19 22:19:27 2024 +0100
@@ -1,5 +1,6 @@
 (*  Title:      Pure/ROOT.ML
     Author:     Makarius
+    UUID:       f8791cc7-32d7-44a6-8a15-e6a7f849fd2c
 
 Main entry point for the Isabelle/Pure bootstrap process.
 

--- a/src/Pure/ROOT.scala	Thu Dec 19 17:01:54 2024 +0000
+++ b/src/Pure/ROOT.scala	Thu Dec 19 22:19:27 2024 +0100
@@ -1,5 +1,6 @@
 /*  Title:      Pure/ROOT.scala
     Author:     Makarius
+    UUID:       d4ac0ad0-9374-4722-b755-018dd6dd0e3b
 
 Root of isabelle package.
 */
@@ -29,4 +30,3 @@
   def if_proper[A](x: Iterable[A], body: => String): String = Library.if_proper(x, body)
   def if_proper(b: Boolean, body: => String): String = Library.if_proper(b, body)
 }
-