Answer architecture round 3: New loads only sources without an index and what they read, an entry drops reads, ErrLoad sits beside New, the manifest decoder moves to manifest.go and names each mistake once as jsonvalue.Kind words it

datatype.go

@@ -7,6 +7,7 @@ import (
 	"github.com/larvit/fejkdata/internal/datatype"
 	"github.com/larvit/fejkdata/internal/grammar"
 	"github.com/larvit/fejkdata/internal/invariant"
+	"github.com/larvit/fejkdata/internal/jsonvalue"
 )
 
 // DataType is what a record column holds, which decides how a record writes its value. It
@@ -29,7 +30,7 @@ func datatypeOf(m map[string]any, pos position) (*DataType, error) {
 	}
 	name, ok := v.(string)
 	if !ok {
-		return nil, fmt.Errorf("datatype must be a string, not %s", jsonKind(v))
+		return nil, fmt.Errorf("datatype must be a string, not %s", jsonvalue.Kind(v))
 	}
 	for d := DataTypeString; d < datatype.Count; d++ {
 		if name != d.String() {