Add transform resolver wiring

internal/publish/output.go

@@ -19,7 +19,11 @@ func PlanOutputs(ctx context.Context, req Request) ([]Output, error) {
 		outputs = append(outputs, sourceOutputs...)
 	}
 	if req.Publish.HTML {
-		generatedOutputs, err := markdownTransformer().Generate(ctx, transform.Request{
+		transformer, err := resolveTransformer(req.Transformers, transform.MarkdownToHTML)
+		if err != nil {
+			return nil, err
+		}
+		generatedOutputs, err := transformer.Generate(ctx, transform.Request{
 			SourceBundle:  req.SourceBundle,
 			SourceBackend: req.SourceBackend,
 		})
@@ -47,6 +51,17 @@ func PlanOutputs(ctx context.Context, req Request) ([]Output, error) {
 	return outputs, nil
 }
 
+func resolveTransformer(resolver TransformerResolver, name string) (transform.Transformer, error) {
+	if resolver == nil {
+		return nil, fmt.Errorf("transformer resolver is required for %s", name)
+	}
+	transformer, ok := resolver.Get(name)
+	if !ok {
+		return nil, fmt.Errorf("transformer %s is not registered", name)
+	}
+	return transformer, nil
+}
+
 func PlanSourceOutputs(req Request) ([]Output, error) {
 	outputs := make([]Output, 0, len(req.SourceBundle.Manifest.Files))
 	for _, file := range req.SourceBundle.Manifest.Files {