Summary

• Send the standard Flight SQL CloseSession action when closing a client.
• Verify that the server reports the session as closed.
• Close the underlying Flight transport even when session cleanup fails.

Closing the PyArrow FlightClient shuts down the transport, but it does not invalidate the server session. Altertable keeps an abandoned session until its four-hour TTL expires. This becomes more costly when dbt uses one session per worker thread.

The client now sends the protocol-defined empty CloseSessionRequest before closing the transport and validates the returned CloseSessionResult. The transport close runs in finally, so a cleanup RPC failure cannot leak the local transport. The original cleanup error still propagates to the caller.

Apache Arrow documents CloseSession as the operation that closes and invalidates the current session context: https://arrow.apache.org/docs/format/FlightSql.html#flight-server-session-management