The salvaged helper cleared its line buffer on entry. Inside run_script's
tokio::select! loop, a stdout line arrival cancels the in-flight stderr
read (and vice versa); read_until had already consumed bytes into the
buffer, and the next call's clear() silently dropped that partial line.
Keep partially-read bytes across cancellation (clear only after a full
line is decoded) and emit an unterminated final line at EOF instead of
swallowing it. Adds a cancellation regression test (fails against the
clear-on-entry version) and an EOF-tail test.
teknium1
8fe9706da8