merge 56005 56320 56319 thanks This doesn't look Guix System-specific to me and looks to have the same issue (i.e., something about write_wait_fd) as <https://issues.guix.gnu.org/56005>, so merging into 56005.
Also, is the substitute server being down a hypothesis for the error but not actually known to actually have hapend, or something you have noticed the substitute server being down via other methods and believe it to be a plausible hypothesis for the error cause? In all cases, I believe write_wait_fd: unimplemented to be a bug that needs to be investigated for the root cause and fixed, not something to accumulate work-arounds for and ignore by automatic retries. Greetings, Maxime.
