e2e-provision.sh used a stand-in gateway; this drives the real
continuum-proxy over the real socket, which is what catches the two ends
disagreeing about the provision_printer frame. With no printer named it
proves the failure path (a useful error returns, no row, nothing stored on
the gateway, the code in neither process's log) and that the proxy starts
and connects with no printers file at all. With REAL_HOST/REAL_SERIAL/
REAL_ACCESS_CODE it also proves the success path - telemetry under the new
id, an owner-only store file, and the printer returning after a restart
from the store alone. It only connects and listens; it sends no command.
