Ansible ERROR! 'retries' is not a valid attribute for a TaskInclude - ansible

Question

My requirement is to run the script stop-all as many times (5 retries) until the output of ps -fu user1 |wc -l becomes less than 2.
I wrote the below ansible playbook for the same:
cat stop.yml
- hosts: dest_nodes
tasks:
- name: Start service
include_tasks: "{{ playbook-dir }}/inner.yml"
retries: 5
delay: 4
until: stopprocesscount.stdout is version('2', '<')
cat inner.yml
- name: Start service
shell: ~/stop-all
register: stopprocess
- name: Start service
shell: ps -fu user1 |wc -l
register: stopprocesscount
However, I get the below error running the playbook.
ERROR! 'retries' is not a valid attribute for a TaskInclude
The error appears to be in '/app/playbook/stop.yml': line 19, column 9, but may
be elsewhere in the file depending on the exact syntax problem.
The offending line appears to be:
- name: Start service
^ here
Can you please suggest?

Answer 1

First of all, correct the indentation of tasks in inner.yml. Secondly, remove retries, delay and until from stop.yml and move them to specific task as these are task level parameters.
Since you need to retry one task based on another task, you can just combine the script and command and extract the result of wc -l command like below:
Since stdout_lines will contain list of strings and version requires int hence the conversion.
inner.yml
- name: Start service
shell: ~/stop-all; ps -fu user1 | wc -l
register: stopprocesscount
retries: 5
delay: 4
until: stopprocesscount.stdout_lines[stopprocesscount.stdout_lines | length - 1] | int is version('2', '<')
stop.yml
- hosts: dest_nodes
tasks:
- name: Start service
include_tasks: "{{ playbook-dir }}/inner.yml"

Answer 2

Not all task attributes work with all task (here TaskInclude task).
There is no clear documentation, such a compatibility matrix, but the error message here is quite clear "is not a valid attribute".
By instance:
You cant loop a Block: 'with_items' is not a valid attribute for a Block
You cant async a TaskInclude, see https://github.com/ansible/ansible/issues/57051.