New sandboxes start with the current web proxy relay

A new sandbox starts from a copy of a machine Runtime booted ahead of time. Those copies were rebuilt only when the guest agent changed, so a change to the web proxy relay alone, such as the removal of the 40 ms wait on responses, reached only sandboxes that booted from scratch. Each copy now records everything it booted with, and a host rebuilds any copy that differs from what a fresh boot would run.