Observe claimed prepared executions

prepared_execution.go

@@ -11,6 +11,9 @@ const preparedExecutionString = "promptkit.PreparedExecution{opaque}"
 // PreparedExecution contains no supported serializable state and cannot be
 // used as a restartable job. Copying the value preserves the same shared
 // lifecycle; it does not create another execution attempt.
+// A successful PrepareExecution may retain an Observer function in this
+// handle's private payload. The callback and other private execution settings
+// are cleared on claim completion or Discard. Details never exposes them.
 type PreparedExecution struct {
 	internal *usecase.PreparedExecution
 }