Can I use Postgres rules to reset session variables before/after queries?

I am using Postgres row level security and I wish to ensure it is not
possible for a specific session variable (that holds a tenant id) to remain
set in between transactions / queries.

The reason is because this is a web application that pools sessions and the
session is shared between user web queries - if that session variable is
set but not cleared, then it is possible that the next query - which is for
a different application user - might be executed using the session variable
from the previous query.

I wish to ensure that the only session variables that can be used are LOCAL
session variables (which must be used only in a transaction and are
temporary and do not remain set in the session after the transaction has
ended).

So the solution I have come up with is to use the Postgres rules system,
and clear the session variable using RESET or SET in between every
transaction or query. RESET
https://www.postgresql.org/docs/9.1/sql-reset.html or SET
https://www.postgresql.org/docs/9.1/sql-set.html both before and after
every SELECT, INSERT, UPDATE, DELETE query.

Although the Postgres rules system appears to have the capabilities to do
this but I cannot find much detail.

A google search says there are not many answers relating to "postgres
rules" and "session variables"

Can anyone suggest if session variables can be SET/RESET using Postgres
rules, or optionally perhaps there is a better way to do so?

thanks