Error handling when 'guix substitute' dies

[Ada Stevenson]

Hi Guix,

I have this gripe with usability regarding using substitutes.

Sometimes, usually when I'm on an enterprise network like my 
university's of library's wifi, the `guix substitute` process dies with 
a "TLS error in procedure 'write_to_session_record_port': Error in the 
push function" error message. My connection is rock-solid otherwise, and 
sometimes it doesn't happen at all.

I'm not sure if this is a fault in the actual Guix code, or there's some 
Guile library somewhere that has this bug. Anyway, I think it would be a 
useful feature to have a way to automatically restart the `guix 
substitute` process or otherwise recover from this error. Some sort of 
`--restart=no.restarts.permitted` flag. Whenever I'm updating my system 
I tend to leave and do something else, and when this happens I come back 
and nothing's actually been done, and the error is transient so I don't 
gain anything from seeing this message.

I workaround could potentially be wrapping `guix upgrade` and the like 
in a script that keeps on restarting the commands until they exit with 
0. This seems a little clunky and fragile, especially if there's an 
actually fatal error, eg. my config is not valid.

What do you guys think? Would this be something that people would be 
interested in? Or would it be better to try and find out why there's 
these transient errors (a way more time-consuming effort, I fear). Does 
anyone else have this issue?

Warmly,

Ada