pkg install nodejs
npm -v
node -v
pkg install git
if above can work doors open much more beyond python - python is lightest best
Discussion
I have `nodejs-lts` installed on my termux env, but have yet to try any serious projects on it. Python nostr_relay was a must-have for my needs because it supports so many NIPS out of the box (and isn't particularly bloated once installed as some other langs implementations).
Agree though that having some nodejs nostr tools on termux *would* be nifty.
try bostr n see if works lts
Would be a worthy experiment - termux handles using nginx reverse proxies just fine.
"degree of mobility n portability with self custody + secure" with hardware price as key factor can be easily solved by buying dirt cheap new/used HEADLESS minipc minimal RAM CPU X64 - full ubuntu / other linux - hence wasting time on andriod is useless if not work in one shot try - no need reinventing wheel - 12V from car or battery take it anywhere in camping or vacation or in backpack - just not in pocket - far cheaper than high RAM HDD expensive phone device 
Oh I already tinker with small machines, especially the rockchip boards w/ gentoo. Getting relay on a device I already had laying around (and are ubiquitous) was simply a fun and interesting exercise.
If you are adventurous and your model of phone has unlocked bootloader, entirely possible to do away with Android completely and just load up a busybox based kernel!
exactly -> purpose / power / price