Report a Task outcome; drives the existing update_background_task FSM.

MODULE-token only, restricted to the expanse module via AUTHENTICATION_ALLOWED_MODULES (mirrors AccountInstallationViewSet). "Internal" means service-to-service, NOT a private network path: like every module-authenticated endpoint in Connect it is reached THROUGH Kong (mounted under public/v1/devops/tasks), which validates the ApiKey MODULE:<expanse-token> and injects the Connect-Auth context this auth class decodes. No portal user or account token can authenticate (a non-module context fails validate_context), so it is never user-reachable.