fix: comma-join array attributes in editor preview postMessage

.changeset/tabbed-posts-preview-category-fix.md

@@ -0,0 +1,5 @@
+---
+"@devgateway/dvz-ui-react": patch
+---
+
+Fix TCDICORE-601: the Gutenberg block editor's live preview for Tabbed Posts (and other blocks with array attributes such as `categories`) sent array attribute values to the preview iframe as JSON-stringified arrays (e.g. `"[5,7]"`), while the published front end joins them as comma-separated strings (`"5,7"`). The mismatch produced malformed REST query parameters (`&category=[5,7]`) that WordPress could not parse, so the live preview showed incorrectly-filtered posts even though the published page rendered correctly. Array attributes are now comma-joined in `PreviewComponent.tsx` to match the front-end save format; non-array object attributes are unaffected.

packages/dvz-ui/src/layout/PreviewComponent.tsx

@@ -28,7 +28,9 @@ const PreviewComponentParameterParser = () => {
             const newParams: Record<string, string> = { ...paramPropsRef.current };
             Object.keys(data).forEach(k => {
                 newParams["data-" + k.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase()] =
-                    typeof data[k] === 'object' ? JSON.stringify(data[k]) : data[k];
+                    typeof data[k] === 'object'
+                        ? (Array.isArray(data[k]) ? data[k].join(',') : JSON.stringify(data[k]))
+                        : data[k];
             });
             setParamProps(newParams);
         }