i have made progress on bisecting the issue i posted. the host is
   behind cloudflare :/ . that seems like a big possible related factor.
   the error does not happen when i run curl simultaneously to the failing
   request (prior, terminates after start, or after, terminates before
   end). so big suspects include triggering on headers, personal
   hallucination, system compromise.
   as it try to diagnose it my muscles contract and begin kind of
   vibrating, in ways that pull me away from what i'm doing. my body
   constantly tries to make errors that harm my work: i already ctrl-c'd
   one long-running process when i was trying to just rerun a test without
   ctrl-c'ing anything.
   i'd really like to video or eeg these weird personal misbehaviors. log
   storage first, though, or i'll just delete the log!