but the SessionLogReader is related to the Session log, isn't?
No it's not. It's a reader for an XML log.
A session log is not machine-readable.
but the SessionLogReader is related to the Session log, isn't? So we could (in the future) add the logging integration there.
No session log is a plain text (Session.SessionLogPath). The XML log is an internal thing, not exposed in any way.
The session log, it that the current XML log? Isn't that the SessionLogReader and that is also using the Logger?
Anyway, debug log for now is a good step.
Though that's for a debug log. You primarily wanted a session log. But that would be way more difficult as session log is actually produced by an internal WinSCP.exe process, not by any .NET code.