azure-bicep already deploys custom_nested_stacks (arm/linked_deployment_custom.go), but their outputs never reach the phone-home payload — so {{ .nuon.install_stack.outputs.custom_nested_stacks.* }} resolves on aws and silently never populates on azure.

• collect each custom deployment's template output keys during composition
• add them to the phone-home script as env vars ([string(reference('<deployment>').outputs.<key>.value)]) and a custom_nested_stacks payload field mirroring the aws lambda shape, with dependsOn on each custom deployment
• reorder template composition so the phone-home resource is built after custom deployments
• reject custom_nested_stacks on gcp-terraform at config parse — the gcp renderer ignores them, so today they validate, upload, and then silently do nothing

Non-string ARM outputs are serialized with string().