ADD type property to indicate the iframe.html was reachable && test i…

…f it's reachable from node

lib/core/src/server/manager/manager-config.js

@@ -2,6 +2,7 @@ import path from 'path';
 import fs from 'fs-extra';
 import findUp from 'find-up';
 import resolveFrom from 'resolve-from';
+import fetch from 'node-fetch';
 
 import { logger } from '@storybook/node-logger';
 
@@ -91,6 +92,17 @@ async function getManagerWebpackConfig(options, presets) {
   }
   if (autoRefs || definedRefs) {
     entries.push(path.resolve(path.join(options.configDir, `generated-refs.js`)));
+
+    // verify the refs are publicly reachable, if they are not we'll require stories.json at runtime, otherwise the ref won't work
+    await Promise.all(
+      Object.entries(refs).map(async ([k, value]) => {
+        const { ok } = await fetch(`${value.url}/iframe.html`).catch((e) => ({
+          ok: false,
+        }));
+
+        refs[k] = { ...value, type: ok ? 'server-checked' : 'unknown' };
+      })
+    );
   }
 
   return presets.apply('managerWebpack', {}, { ...options, babelOptions, entries, refs });