term.ReadPassword reads the terminal with a raw read that returns 0
bytes at the end of input and takes that as nothing yet, so Ctrl-D at
the prompt did nothing. On the Unix systems the prompt now sets the
terminal as ReadPassword does and reads the line from standard input,
which reports the end of input; elsewhere, such as Windows, it still
uses ReadPassword. Ctrl-D with nothing typed gives an empty mnemonic,
refused with status 1, and the terminal settings are put back. A test
types Ctrl-D at the prompt on a pseudo-terminal.
Unverified: the prompt was run only on Linux; other systems were built.
Deviation: a Ctrl-H byte is no longer a backspace at the prompt.
Model: opus-5-5
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>
