os/exec's StdoutPipe Footgun: How cmd.Wait() Ate My Last Frame (Twice)

Thu, 17 Sep 2026 20:12:00 -0700

shipmates spends most of its life spawning claude (and codex) processes and reading newline-delimited JSON off their stdout. The last frame of a turn is the important one. It’s a result frame with the cost, the model and the final text. Stderr matters too, because that’s where Claude Code tells you Invalid API key · Please run /login. For a while I was throwing both away under load. The cause is documented right there in the os/exec godoc. I fixed it in one package and then found the exact same bug again a month later in another.

Os-Exec on Luther Monson

os/exec's StdoutPipe Footgun: How cmd.Wait() Ate My Last Frame (Twice)