Invalid many — showcase/invalid-many

# Expected to fail validation and list every problem, not just the first:
# unknown node type, duplicate node id, dangling non-Terminal leaf, and a
# publish that names a missing destination.
server:
  addr: ":8080"
  max_body_bytes: 1024

destinations:
  primary:
    type: webhook
    webhook:
      url: "https://example.test/hooks"

flows:
  broken:
    nodes:
      - {id: in, type: http_trigger, path: /w, methods: [POST]}
      - {id: in, type: read_body, max_bytes: 1024}
      - {id: ghost, type: not_a_real_node}
      - {id: dangling, type: envelope}
      - {id: out, type: publish, destination: missing-dest, target: t}
    edges: [in>ghost]