Fixed portal preview resize and cached page bugs

no issue

- moved `@onLoad` trigger from `load` event to the `makeVisible()` task so that consumer code isn't called before load has fully finished
  - fixes issue with portal sometimes not being ready when we perform the resize on the membership screen
- added guid as a cache-busting `?v={guid}` query param
  - fixes issue where preview iframe can load stale data after a settings change resulting in a blank preview after going from "nobody" to "invite/anybody" because the loaded homepage is stale and doesn't have the portal script injected

ghost/admin/app/components/gh-site-iframe.js

@@ -18,7 +18,13 @@ export default class GhSiteIframeComponent extends Component {
     }
 
     get srcUrl() {
-        return this.args.src || `${this.config.get('blogUrl')}/`;
+        const srcUrl = new URL(this.args.src || `${this.config.get('blogUrl')}/`);
+
+        if (this.args.guid) {
+            srcUrl.searchParams.set('v', this.args.guid);
+        }
+
+        return srcUrl.href;
     }
 
     @action
@@ -43,10 +49,13 @@ export default class GhSiteIframeComponent extends Component {
 
     @action
     onLoad(event) {
+        this.iframe = event.target;
+
         if (this.args.invisibleUntilLoaded && typeof this.args.invisibleUntilLoaded === 'boolean') {
             this.makeVisible.perform();
+        } else {
+            this.args.onLoad?.(this.iframe);
         }
-        this.args.onLoad?.(event);
     }
 
     @action
@@ -73,5 +82,6 @@ export default class GhSiteIframeComponent extends Component {
         // allows portal to render it's overlay and prevent site background flashes
         yield timeout(100);
         this.isInvisible = false;
+        this.args.onLoad?.(this.iframe);
     }
 }

ghost/admin/app/controllers/settings/membership.js

@@ -239,8 +239,8 @@ export default class MembersAccessController extends Controller {
     }
 
     @action
-    portalPreviewLoaded(event) {
-        this.portalPreviewIframe = event.target;
+    portalPreviewLoaded(iframe) {
+        this.portalPreviewIframe = iframe;
         this.resizePortalPreviewTask.perform();
     }