Function validate_remote_schema 

fn validate_remote_schema(
    expected: &Schema,
    actual: &Schema,
    source: &str,
) -> Result<()>

Validates the remote schema before positional column handling.

Field metadata (indexing/encoding/compression hints) is non-semantic at this boundary and is ignored: two fields are equal when their name and data type match and their nullability is compatible (see fields_semantically_equal). A timestamp timezone difference is the only intentional exception, accepted when the fields share the same timestamp unit, distinct timezones, equal name, and compatible nullability. Top-level Arrow schema metadata is non-semantic at this boundary as well. JSON columns are compared semantically (see json_fields_compatible) because their wire and decoded representations use different physical arrow types.