brn I have just tried both configurations but none of them seems to work. In terms of the session token It was initially set up automatic, I just downloaded and installed the extension and put my credentials to log in of course and It works perfect.
Then I navigated to my API portal under Kagi settings to generate a new API token in order to have access to a more robust summarisation, so I copied the token and pasted on the Kagi Extension settings so I was able to summarise a page using Agnes engine, but after a minute or so, the API token wasn't there.
For testing purposes I configured the session token manually on the extension and it is no different from the automatic log in method. The session token remains with no issues at all. So it is all about the Universal Summarise API Token.
