Address reviewer findings: reference hint, consumer-terms type errors, misuse exit code, immutability and parity docs

render.go

@@ -32,6 +32,9 @@ func (f *Generator) Fake(path string) (string, error) {
 
 // Template is an inline template compiled, referenced and validated against a
 // generator's loaded data once, ready to render many times with [Template.Fake].
+// It is safe for concurrent use: Fake serializes on its generator's lock, so a
+// seeded sequence is reproducible only when a generator — and its templates — are
+// drawn from one goroutine.
 type Template struct {
 	g *Generator
 	n node
@@ -48,6 +51,10 @@ func (t *Template) Fake() string {
 // binds its references against the loaded tree, so repeated renders pay the
 // compile and validation once. It shares [New]'s guarantees: a bad template errors
 // here, and rendering cannot fail.
+// NewTemplate runs the same fences loadData does for a category, scoped to one
+// inline node with everything but checkNoCycles: a reference binds only into the
+// loaded tree, which has no path into this node, so rendering it cannot reach
+// itself. A new fence belongs in both places (loadData and here).
 func (f *Generator) NewTemplate(input string) (*Template, error) {
 	n, err := compileInput(input)
 	if err != nil {
@@ -56,8 +63,6 @@ func (f *Generator) NewTemplate(input string) (*Template, error) {
 	if err := linkNodeRefs(n, f.categories); err != nil {
 		return nil, fmt.Errorf("fejkdata: %w", err)
 	}
-	// No cycle is possible: a reference binds only into the loaded tree, which has
-	// no path into this node, so rendering it cannot reach itself.
 	if err := checkNodeRepeatReach(n); err != nil {
 		return nil, fmt.Errorf("fejkdata: %w", err)
 	}