core-compat-api: hide page header for compat-wrapped legacy pages

Legacy plugins already render their own headers, so the additional
PageLayout header from the PageBlueprint results in duplicate headers.
Pass noHeader: true in both convertLegacyPageExtension and
collectLegacyRoutes to suppress the outer header.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

.changeset/hide-compat-wrapper-headers.md

@@ -0,0 +1,5 @@
+---
+'@backstage/core-compat-api': patch
+---
+
+Hide the default page header for pages created through the compatibility wrappers, since legacy plugins already render their own headers.

packages/core-compat-api/src/collectLegacyRoutes.tsx

@@ -236,6 +236,7 @@ export function collectLegacyRoutes(
           // todo(blam): why do we not use the inputs here?
           return originalFactory({
             path: normalizeRoutePath(path),
+            noHeader: true,
             routeRef: routeRef ? convertLegacyRouteRef(routeRef) : undefined,
             loader: async () =>
               compatWrapper(

packages/core-compat-api/src/convertLegacyPageExtension.tsx

@@ -60,6 +60,7 @@ export function convertLegacyPageExtension(
     name: overrides?.name ?? kebabName,
     params: {
       path: overrides?.path ?? `/${kebabName}`,
+      noHeader: true,
       routeRef: mountPoint && convertLegacyRouteRef(mountPoint),
       loader: async () => compatWrapper(element),
     },