c39703ed0d
Fixes #69 ## Why `getenv` returned the fallback whenever `os.Getenv` was empty, so an intentionally-empty env var could not override a non-empty default. ## Changes - Use `os.LookupEnv` to distinguish unset from set-but-empty. ## Validation - `make e2e` passes. Reviewed-on: #85 Co-authored-by: Ben Vincent <ben@unkin.net> Co-committed-by: Ben Vincent <ben@unkin.net>