Create custom list of dicts in Ansible

I need to create in Ansible a variable with set_fact as a list of dictionaries.

In particular I have previous.results as:

{
  path: /aaa
  files: [f1.txt, f2.txt]
  [other dict content]
},
{
  path: /bbb
  files: [f3.txt]
  [other dict content]
}

and I want to have:

[{path: /aaa, files:[f1.txt, f2.txt]}, {path: /bbb, files: [f3.txt]}]

I tried with the following code:

  - name: init
    ansible.builtin.set_fact:
      files: "{{ files|default([]) + [ { path: item['path'], files: item.keys() } ] }}"
    with_items: "{{ previous.results }}"

But I get:

fatal: [localhost]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: 'path' is undefined. 'path' is undefined\n\nThe error appears to be in 'test-playbook.yaml': line 47, column 5, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n  - name: init\n    ^ here\n"}

My objective is to create these files locally and then add content (item.values()) following this stackoverflow solution. I'm treating files var as objs in the solution I linked.

You don't need any step to transform your initial list of dicts, you can use it as it is:

---
- hosts: localhost
  gather_facts: false

  vars:
    previous:
      results:
        - path: /aaa
          files: [f1.txt, f2.txt]
          toto: 1
          pipo: 2
        - path: /bbb
          files: [f3.txt]
          toto: 3
          pipo: 4

  tasks:
    - name: Show the result in a debug task
      ansible.builtin.debug:
        msg: "I would create {{ item.0.path }}/{{ item.1 }}"
      # Note the below line is strictly equivalent to:
      # with_subelements:
      #   - "{{ previous.results }}"
      #   - files
      loop: "{{ previous.results | subelements('files') }}"
      # Adding control to limit loop output to only a few data
      loop_control:
        label: "{{ item.0.path }}, {{ item.1 }}"

The above playbook gives:

PLAY [localhost] **************************************************************************************************************************************************************************************************

TASK [Show the result in a debug task] ****************************************************************************************************************************************************************************
ok: [localhost] => (item=/aaa, f1.txt) => {
    "msg": "I would create /aaa/f1.txt"
}
ok: [localhost] => (item=/aaa, f2.txt) => {
    "msg": "I would create /aaa/f2.txt"
}
ok: [localhost] => (item=/bbb, f3.txt) => {
    "msg": "I would create /bbb/f3.txt"
}

PLAY RECAP ********************************************************************************************************************************************************************************************************
localhost                  : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0