Address Greptile review feedback:
1. Wrap os.userInfo() in try/catch — it throws SystemError when the
current UID has no /etc/passwd entry (e.g. `docker run --user 1234`
with a minimal image). Falls back to process.env.HOME gracefully.
2. Add HOME to VOLATILE_ENV_KEY_EXACT so the discovery cache key is
not affected by the caller-supplied HOME vs the resolved HOME.
os.userInfo().homedir is constant for the process lifetime, so
HOME adds no useful cache differentiation.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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