Add comment for bug

src/prefect/engine.py

@@ -1653,7 +1653,13 @@ def resolve_input(expr, context):
         # Do not allow uncompleted upstreams except failures when `allow_failure` has
         # been used
         if not state.is_completed() and not (
-            isinstance(context.get("annotation"), allow_failure) and state.is_failed()
+            # TODO: Note that the contextual annotation here is only at the current level
+            #       if `allow_failure` is used then another annotation is used, this will
+            #       incorrectly evaulate to false — to resolve this, we must track all
+            #       annotations wrapping the current expression but this is not yet
+            #       implemented.
+            isinstance(context.get("annotation"), allow_failure)
+            and state.is_failed()
         ):
             raise UpstreamTaskError(
                 f"Upstream task run '{state.state_details.task_run_id}' did not reach a 'COMPLETED' state."