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

node.go

@@ -193,22 +193,6 @@ func typedOrText(text string, ds ...DataType) error {
 
 // jsonKind names the kind of a JSON value an option cannot take, in the data format's own
 // terms rather than the decoding library's.
-func jsonKind(v any) string {
-	switch v.(type) {
-	case json.Number:
-		return "a number"
-	case bool:
-		return "a boolean"
-	case string:
-		return "a string"
-	case []any:
-		return "a list"
-	case map[string]any:
-		return "an object"
-	}
-	return fmt.Sprintf("%T", v)
-}
-
 func compileString(s string) (*template, error) {
 	toks, unbound, err := parseChecked(s, nil)
 	if err != nil {
@@ -332,7 +316,7 @@ func readOptions(m map[string]any, pos position) (templateOptions, error) {
 	}
 	if sv, ok := m["separator"]; ok {
 		if o.separator, ok = sv.(string); !ok {
-			return o, fmt.Errorf("separator must be a string, not %s", jsonKind(sv))
+			return o, fmt.Errorf("separator must be a string, not %s", jsonvalue.Kind(sv))
 		}
 	}
 	return o, nil
@@ -365,7 +349,7 @@ func repeatOf(m map[string]any) (int, error) {
 	}
 	r, ok := numberOf(rv)
 	if !ok {
-		return 0, fmt.Errorf("repeat must be a number, not %s", jsonKind(rv))
+		return 0, fmt.Errorf("repeat must be a number, not %s", jsonvalue.Kind(rv))
 	}
 	if err := notTiny("repeat", rv, r); err != nil {
 		return 0, err
@@ -392,7 +376,7 @@ func weightOf(raw any) (float64, error) {
 	}
 	w, ok := numberOf(wv)
 	if !ok {
-		return 0, fmt.Errorf(`weight is an option and takes a number, not %s; a field cannot be named "weight"`, jsonKind(wv))
+		return 0, fmt.Errorf(`weight is an option and takes a number, not %s; a field cannot be named "weight"`, jsonvalue.Kind(wv))
 	}
 	if w < 0 || math.IsInf(w, 0) {
 		return 0, fmt.Errorf("weight must be a finite number of 0 or more, got %v", wv)