diff -r 90fbcdafb34e -r 32ca3d1283de src/Pure/Build/build_process.scala
--- a/src/Pure/Build/build_process.scala	Thu Feb 22 21:03:55 2024 +0100
+++ b/src/Pure/Build/build_process.scala	Thu Feb 22 21:28:55 2024 +0100
@@ -1107,6 +1107,15 @@
   }
 
 
+  /* prepare */
+
+  def prepare(): Unit = {
+    for (name <- build_context.clean_sessions) {
+      store.clean_output(_database_server, name, progress = progress)
+    }
+  }
+
+
   /* run */
 
   def run(): Build.Results = {