Minor: a serialisation related fix and an additional explainer comment in SerializedBytes

core/src/main/kotlin/core/serialization/Kryo.kt

@@ -68,6 +68,7 @@ val THREAD_LOCAL_KRYO = ThreadLocal.withInitial { createKryo() }
  * to get the original object back.
  */
 class SerializedBytes<T : Any>(bits: ByteArray) : OpaqueBytes(bits) {
+    // It's OK to use lazy here because SerializedBytes is configured to use the ImmutableClassSerializer.
     val hash: SecureHash by lazy { bits.sha256() }
 
     fun writeToFile(path: Path) = Files.write(path, bits)

core/src/main/kotlin/core/utilities/ProgressTracker.kt

@@ -65,8 +65,13 @@ class ProgressTracker(vararg steps: Step) {
         override val label: String get() = currentLabel
     }
 
-    object UNSTARTED : Step("Unstarted")
-    object DONE : Step("Done")
+    // Sentinel objects. Overrides equals() to survive process restarts and serialization.
+    object UNSTARTED : Step("Unstarted") {
+        override fun equals(other: Any?) = other is UNSTARTED
+    }
+    object DONE : Step("Done") {
+        override fun equals(other: Any?) = other is DONE
+    }
 
     /** The steps in this tracker, same as the steps passed to the constructor but with UNSTARTED and DONE inserted. */
     val steps = arrayOf(UNSTARTED, *steps, DONE)