ansible-role-ssh_host_key/tasks/save.yml

---

- name: make sure host_vars directory is present for host
  local_action: file
  args:
    path: "{{inventory_dir}}/host_vars/{{inventory_hostname}}"
    state: directory

- name: record ssh host key in host_vars
  local_action: copy
  args:
    content:
      ssh_host_key_ed25519_public: "{{ ssh_host_key_ed25519_public }}"
    dest: "{{inventory_dir}}/host_vars/{{inventory_hostname}}/ssh_host_key.auto.json"