Fix up some EL10 compatibility

* EL9 has python3.9 as system Python
* EL10 has bumped up this to python3.12
* Added a short novel for future archaeologists.

Change-Id: Ie9ee25207cee5b5aed773c2dc89a05bf6243069e

roles/ensure-python/tasks/main.yaml

@@ -36,18 +36,49 @@
       become: yes
 
     - name: Install specified version of python interpreter and development files (RPM)
+      # NOTE(jan.gutter): this section has many pitfalls, and lacks test
+      # coverage. Rather than rewrite the logic to be more pleasing, and risk
+      # changing the behavior for folks who depend on edge cases, it has been
+      # preferrable to amend this with special cases, for the time being.
+      #
+      # RPM distros have diverged in behavior: packages and aliases are not
+      # consistent. The following example illustrates some known behavior for
+      # python_version "3.12"
+      #
+      # Fedora/EL9/EL10 (manually tested):
+      #   working:
+      #     - python312
+      #     - python3.12
+      #     - python3.12-devel
+      #   not working:
+      #     - python312-devel
+      #
+      # OpenSuSE (inferred from rpmfind.net):
+      #   working:
+      #     - python312
+      #     - python312-devel
+      #   not working:
+      #     - python3.12
+      #     - python3.12-devel
       when:
         - ansible_distribution == 'CentOS' or ansible_distribution == 'RedHat'
       block:
         - name: Set default RPM package name
+          # NOTE(jan.gutter): this is likely faulty - but, without testing,
+          # touching it would taunt Hyrum's law. EL9/EL10 paths override the
+          # exception below this task for system python versions.
           set_fact:
             rpm_python_pkg_name: python{{ python_version | replace('.', '') }}-devel
-        - name: Set RPM package name for CentOS/RHEL 9 and Python 3.9
+        - name: Set RPM package name for CentOS/RHEL 9/10
+          # Special case when the default system python is being used.
           set_fact:
             rpm_python_pkg_name: python3-devel
-          when:
-            - ansible_distribution_major_version == '9'
-            - python_version|string == '3.9'
+          when: >-
+            (ansible_distribution_major_version == '9' and
+            python_version|string == '3.9')
+            or
+            (ansible_distribution_major_version == '10' and
+            python_version|string == '3.12')
         - name: Install RPM package
           package:
             name: "{{ rpm_python_pkg_name }}"