Where should the port interfaces in hexagonal architecture go? in application or domain?

I have this question, I have not reached a clear conclusion and there seems to be a divergence of opinion on the matter, so I would like to know your point of view and why, I would like to know what the ‘right’ way is or at least be able to draw my own conclusion based on your opinions.

Where "Ports" go:

• In terms of the interface (definition) that defines a port, you could define them in the Application Layer, but you would not define them in the Domain Layer.
• In terms of port implementation, they sit in the Adaptors Layer.

Alistair Cockburns formal description (from 2006 see https://wiki.c2.com/?PortsAndAdaptersArchitecture and https://wiki.c2.com/?HexagonalArchitecture) is text-based and written in a fairly conversational tone. Unfortunately Cockburn refers to a diagram which is no-longer available with the posted text.

Cockburn does explicitly name parts of the architectural style, and heavily implies formal names for the layers but does not go as far as doing so beyond “Outside“, “Transformer” (aka “Adaptor“), “Application“, “Domain“. Referring to the inner 2 as “Application Layer“ and “Domain Layer” does not seem unreasonable.

In the Hexagonal post he explicitly writes:

OUTSIDE <-> transformer <--> ( application  <->  domain )

He later (in the renaming to Port and Adaptors) explicitly talks about “changing that drawing to show 'adapter' instead of 'transformer'“, so we could reasonably refer to that 3rd layer as the “Adaptor Layer”.

OUTSIDE <-> Adaptor <--> ( application  <->  domain )

My guess is that as a diagram - thinking of how Clean is often depicted - you'd get something like this:

Lastly, you my find this video helpful in understanding Hexagonal architecture - it's Cockburn himself going into more detail, it's more recent (2017), and includes a code demo, but the audio quality is very poor. https://www.youtube.com/watch?v=th4AgBcrEHA