Story

RHDH allows plugins to extend application-level behaviour like the application header, Reqact content providers & application listeners via the mount points `application/header` , `application/provider` & `application/listener` respectively. As part of adopting Backstage’s New Frontend System, we need to migrate these and create new extensions as per the NFS model or use Blueprint wherever needed.

Background

Dependencies and Blockers

QE impacted work

Documentation impacted work

Acceptance Criteria

• Design the Blueprint first and get approval from the team
• The existing `application/header` , `application/provider`, & `application/listener` mount point is replaced with new extensions implemented using NFS
• Existing functionality must continue to work with no regression after the migration
• Should move the legacy app to app-legacy and the new app with NFS model should be in app
• The header should be displayed in rhdh-plugins, with playwright tests

Note: Check if we can use `AppRootWrapperBlueprint` for the application/provider

Refs:

WG notes: https://docs.google.com/document/d/14G569uZZjST3j--cEX3_IZcwe3iRU091ETcwZ773GXE/edit?tab=t.0#heading=h.bvqw57j2nbwz

NFS migration spike : https://docs.google.com/document/d/1Qb0T1Iu3ego50iO4V7NErSD44NdWSvk5n70pZvj-EmU/edit?tab=t.0#heading=h.zc5io9fn4km1

Backstage docs:
https://backstage.io/docs/frontend-system/architecture/extensions#creating-an-extension