Cannot create sync self message inside an execution specification

[planger]

When I try to create a sync self message in this scenario:

The result is as follows:

I would have expected that the created message would start a new nested execution and that a reply message is being created.

I believe this is because we test whether the to-be-created sync message connects to an execution and, if yes, we don't automatically create an execution. However, it turns out that this test is not a good solution for all scenarios :)

A workaround right now is to first create the execution and then connect a new sync message to its start, however, this is actually very hard to achieve or potentially doesn't work either (I'm able to do that for non-self messages, but not for self-messages).