"Child process STDOUT is trimmed to 100 lines" is useless in most cases. In most cases, this message has no value.
jtreg doesn't tell us whether trimming of STDOUT took place.

I want for jtreg to write
"STDOUT was trimmed to 100 lines. Find full STDOUT in <file_name>" in .jtr file when stdout was actually trimmed, otherwise to write nothing in that regard.