Group::attrs now leaves out an attribute it cannot decode. The agent read
its settings through it, so a store whose float16 (or compression,
quantized_index, WAL mark, signature...) attribute could not be decoded
opened with the default in its place, and no error. /meta is now read
with attrs_with_errors and any unreadable attribute is a Schema error,
as it was before attrs became tolerant. Found by the adversarial review.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>