diff -r 6784eaef7d0c -r d98a99e4eea9 src/Pure/Tools/build_job.scala
--- a/src/Pure/Tools/build_job.scala	Mon Feb 06 12:58:45 2023 +0100
+++ b/src/Pure/Tools/build_job.scala	Mon Feb 06 14:54:15 2023 +0100
@@ -570,7 +570,7 @@
     else Some(Event_Timer.request(Time.now() + info.timeout) { terminate() })
   }
 
-  def join: (Process_Result, String) = {
+  def join: (Process_Result, SHA1.Shasum) = {
     val result1 = future_result.join
 
     val was_timeout =
@@ -585,17 +585,11 @@
       else if (result1.interrupted) result1.error(Output.error_message_text("Interrupt"))
       else result1
 
-    val heap_digest =
+    val heap_shasum =
       if (result2.ok && do_store && store.output_heap(session_name).is_file) {
-        Some(ML_Heap.write_digest(store.output_heap(session_name)))
+        SHA1.shasum(ML_Heap.write_digest(store.output_heap(session_name)), session_name)
       }
-      else None
-
-    val heap_shasum =
-      heap_digest match {
-        case None => ""
-        case Some(digest) => SHA1.shasum(digest, session_name) + "\n"
-      }
+      else SHA1.no_shasum
 
     (result2, heap_shasum)
   }