Debugging features needed

Hello!
    I need a feature that would me allow to debug "live" the work of an application together with a PostgreSQL database.

I think that if I would be able to define a session variable that is visible in pg_stat_activity (or in other system view, table or function) I would be more than happy.
Well, I have described what I see as a partial solution to my problem, the problem being: how to track a specific set of actions at database level of a given application user in the context of session pooling (so the user activity can jump from one session to another of the same pool).
If I would be able to set a "value" to a custom variable, then the app would simply need to set the value at each session usage, but I definitely understand that other mechanisms might help solving the problem (but I do not know any of these).
I think that I can implement a logging mechanism at database level instead (and I have some ideas about how to do that), but logging search is not quite live debugging.
Any help would be highly appreciated, thank you kindly.
Best regards, Cristi Boboc

Best regards, Cristi Boboc