tests/fixtures/{minimal,full}/configs/*.yaml + checked-in expected.bin
golden files, added to test_config_build.py. Catches representation
drift (bytes changing even when decoded content stays correct) that
the existing structural/decode-based assertions can't detect.
config build pipeline: scan the 7 known YAML filenames, validate
each present file, run cross-file business-rule checks, map to
ClusterConfig, serialize. Missing files become empty sections;
schema-valid-but-unmapped fields and undefined references warn to
stderr instead of failing. write_output() handles -o <path>/-o -
and returns the hex SHA-256 digest (printing it is the CLI's job).
