StartupHost

What StartupStateMachine needs from the node it brings up.

Declared in src/libs/libnode/node/StartupHost.hpp.

Detailed description

work-placement §WPK-4 item 6: the startup machine takes no `Node`. It reads these twelve things, and only these, so a host other than `Node`, such as a NodeKit app, can run the same startup. NodeStartupHost answers them from a `Node`.

A host can go away while an asynchronous step of the machine is in flight: alive() says whether it is still there, and every accessor then gives null.