Add previewArgs support for template functions and enhance validation logic for form inputs

plugins/template-function-cookie/src/index.ts

@@ -5,15 +5,18 @@ export const plugin: PluginDefinition = {
     {
       name: 'cookie.value',
       description: 'Read the value of a cookie in the jar, by name',
+      previewArgs: ['name'],
       args: [
         {
           type: 'text',
-          name: 'cookie_name',
+          name: 'name',
           label: 'Cookie Name',
         },
       ],
       async onRender(ctx: Context, args: CallTemplateFunctionArgs): Promise<string | null> {
-        return ctx.cookies.getValue({ name: String(args.values.cookie_name) });
+        // The legacy name was cookie_name, but we changed it
+        const name = args.values.cookie_name ?? args.values.name;
+        return ctx.cookies.getValue({ name: String(name) });
       },
     },
   ],