"parallel output buffering" is nice because

parallel build output is much more useful when several processes' output isn't garbled up together. (source)

but this becomes a problem when workers block (hang forever)
so i dont see their output, and i cant debug them

in debug mode, instead of "block-buffered"
the output should be line-buffered, with the PID as line prefix

similar issue: #545

relevant code

quickfix: always print live output → branch (diff)

edit:
broken: printing garbage <F8>TD instead of line_prefix
fixed by mallocing the line_prefix