I understand why it's difficult, but most in-process connection poolers will manage prepared statements for you even as the connection pool grows and shrinks.

I know it's more complicated, but I imagine pgbouncer could detect "prepare foo as..." and "execute foo(...)" and track whether a given session has had "foo" prepared. If not, rerun the "prepare foo as ..." on a session if "execute foo(...)" is received. That's essentially what the in-process version does.

There would be some complications around conflicts for a given named prepared statement, but that could be solved with some requirements on clients (e.g. use source hash in prepared statement names).