Record subprocess return code, stdout/stderr byte counts and tails, plus raw stdout/stderr/meta files when benchmark CLI subprocesses fail. Surface the structured details in benchmark JSON reports so failed runs can be diagnosed without rerunning expensive cases.
Keep artifacts under each benchmark work root's failures directory, with a temp fallback only when no CBM_CACHE_DIR is present.
Validation: py_compile with cfile in /private/tmp passed, expected-failure wrapper produced error_detail.returncode=37 and raw artifacts, tiny success benchmark returned rc=0 and passed under --min-speedup 0. Temporary work roots and wrapper were cleaned after standalone evidence was saved.
Signed-off-by: Andrew Hundt <ATHundt@gmail.com>
Andrew Hundt
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