Two discoveries from exercising the capture path live:
- docker exec prints its 'executable file not found' OCI error to STDOUT
(a docker quirk), i.e. into the tar pipe — so the exit code (126/127)
is the only trustworthy no-tar signal, and the host-side 'not a tar
archive' noise is a symptom, not the cause. Detect on the code and say
plainly that the image has no tar.
- The two pipe halves shared one stderr file through an O_TRUNC fd and
an O_APPEND fd, racing and overwriting each other's lines — one file
per half, concatenated after.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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