Steps inherited the hand-off console's stdin, so any step that asks a
question blocked forever. Its prompt went to the captured stdout, which
is shown only after the step exits. `gateway start --all` did exactly
this: it saw an interactive console and asked "Install it now so the
gateway starts on login?". The update stopped after `hermes update exit
code: 0` and never relaunched the app.
Steps now read NUL. Prompts see a non-interactive stdin and take their
defaults. The working-directory self-test also checks that a step's
stdin is not a console, and a new test runs it under a real console.
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