envName.toUpperCase() alone turned env 'drill-b' into
CAST_AGE_KEY_FILE_DRILL-B — a variable no POSIX shell can export, so the
injected-key channel (and its process-substitution trick) was unreachable
for every hyphenated environment name, while the refusal advertised it
anyway. Characters outside [A-Z0-9] now map to _; the standing-key path
keeps the exact env name, so names that collide on the variable still
resolve their own keys on disk.
Fixes#102
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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