tl;dr: Does Ansible have a variable containing the current Python interpreter?
As part of my playbook, I am creating a Python script on the controller (to be run by another command), and I want that script to be run by the Python interpreter being used by Ansible. To do this I am trying to set the interpreter in the shebang of the script.
If I were to set the interpreter manually, I could use the ansible_python_interpreter variable (and I have had it working that way). If I don't set the interpreter manually, then Ansible will auto-discover an interpreter, but I can no longer use the ansible_python_interpreter variable because it is not set.
From looking through the documentation I have been unable to find any way to see which interpreter Ansible has auto-detected. Is there something I've missed?
(Ansible version 2.9.10, Python 3.6)

The complete situation:
I am running Ansible on AWX (open-source Ansible Tower), using a custom virtual environment as the runner. I use Hashicorp Vault as a secret management system, rather than keeping secrets in AWX. For access to Vault I use short-lived access tokens, which doesn't work well with AWX's built-in support for pulling secrets from Vault, so instead I do it manually (so that I can supply a Vault token at job launch time). That works well for me, generally.
In this particular case, I am running ansible-vault (yes, there are too many things called 'vault') on the controller to decrypt a secret. I am using the --vault-password-file argument to supply the decryption password via a script. Since the virtual env that I am using already has the hvac package installed, I wish to just use a brief Python script to pull the password from Hashicorp Vault. All works fine, except that I can't figure out how to set the shebang on this script to point at the virtual environment that Ansible is using.
If I can't get a useable answer to this, I suppose I can change to instead pull the password directly into Ansible and then use the --ask-vault-pass flag to pass the password that way. It just seems to me that the interpreter should really be exposed somewhere by Ansible, so I'm trying that first.
With gather_facts: yes you should be able to get the active python using the ansible_facts.python variable.
Does Ansible expose its auto-discovered Python interpreter?