Reserve the reference prefix in authored names, and report one compile error

data.go

@@ -67,6 +67,10 @@ func loadDir(dir string) (*group, error) {
 		if !strings.HasSuffix(e.Name(), ".json") {
 			continue
 		}
+		name := strings.TrimSuffix(e.Name(), ".json")
+		if isRef(name) {
+			return nil, fmt.Errorf("%s: category %q starts with %q, which is reserved for {..path} bindings", full, name, refPrefix)
+		}
 		b, err := os.ReadFile(full)
 		if err != nil {
 			return nil, err
@@ -79,7 +83,7 @@ func loadDir(dir string) (*group, error) {
 		if err != nil {
 			return nil, fmt.Errorf("%s: %w", full, err)
 		}
-		g.children[strings.TrimSuffix(e.Name(), ".json")] = n
+		g.children[name] = n
 	}
 	return g, nil
 }

node.go

@@ -3,6 +3,7 @@ package fakes
 import (
 	"fmt"
 	"math"
+	"sort"
 )
 
 // node is a compiled template element: literal, choice, or template. Compiling
@@ -106,11 +107,19 @@ func compileTemplate(m map[string]any) (node, error) {
 		}
 	}
 	t := &template{format: format, fields: make(map[string]node, len(m)), repeat: repeat, separator: sep}
-	for k, v := range m {
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys) // so which of several bad fields is reported does not vary
+	for _, k := range keys {
 		if k == "format" || k == "weight" || k == "repeat" || k == "separator" {
 			continue
 		}
-		n, err := compile(v)
+		if isRef(k) {
+			return nil, fmt.Errorf("field %q starts with %q, which is reserved for {..path} bindings", k, refPrefix)
+		}
+		n, err := compile(m[k])
 		if err != nil {
 			return nil, fmt.Errorf("field %q: %w", k, err)
 		}

reference.go

@@ -38,8 +38,7 @@ func linkRefs(root map[string]node) error {
 
 // walkNodes calls fn once per contained node, passing the dot path that reaches it,
 // visiting keys in sorted order so which of several broken nodes gets reported does
-// not depend on map iteration. fn runs before a node's children, so a binding it
+// not depend on map iteration.
-// adds to a template's fields is walked too.
 func walkNodes(root map[string]node, fn func(path string, n node) error) error {
 	seen := map[node]bool{}
 	var visit func(string, node) error