feat(ansible): add mysql-rollback playbook for instance cleanup

Add a compensating playbook that removes a single delivered MySQL
instance from a target host. The rollback scope is pinned by
target_hosts + instance_name + data_disk, with pre-task assertions
rejecting instance names or disk paths outside the delivery layout
to prevent accidental deletion.

- stop and disable mysql-delivery@<instance>.service, reset failed state
- remove instance data dir, install dir, config file and run dir

ansible/mysql-rollback.yml

@@ -0,0 +1,79 @@
+---
+- name: Roll back native MySQL delivery instance
+  hosts: "{{ target_hosts }}"
+  become: true
+  gather_facts: false
+  any_errors_fatal: true
+  vars:
+    mysql_instance: "{{ instance_name }}"
+    mysql_data_disk: "{{ data_disk }}"
+    mysql_base_dir: "{{ mysql_data_disk }}/mysql-delivery/{{ mysql_instance }}"
+    mysql_install_dir: "/opt/mysql-delivery/{{ mysql_instance }}"
+    mysql_config_file: "/etc/mysql/mysql-delivery/{{ mysql_instance }}.cnf"
+    mysql_run_dir: "/run/mysql-delivery-{{ mysql_instance }}"
+
+  pre_tasks:
+    - name: Validate rollback target
+      ansible.builtin.assert:
+        that:
+          - mysql_instance is match('^[a-z0-9][a-z0-9-]{0,62}$')
+          - mysql_data_disk is match('^/')
+          - mysql_data_disk != '/'
+          - "'..' not in mysql_data_disk"
+        fail_msg: "Rollback target is outside the native MySQL delivery layout"
+        quiet: true
+
+  tasks:
+    - name: Stop the delivery instance when present
+      ansible.builtin.systemd_service:
+        name: "mysql-delivery@{{ mysql_instance }}.service"
+        state: stopped
+        enabled: false
+      register: mysql_stop_result
+      failed_when: false
+
+    - name: Remove the instance systemd failure state
+      ansible.builtin.command:
+        argv:
+          - systemctl
+          - reset-failed
+          - "mysql-delivery@{{ mysql_instance }}.service"
+      changed_when: false
+      failed_when: false
+
+    - name: Remove the instance configuration
+      ansible.builtin.file:
+        path: "{{ mysql_config_file }}"
+        state: absent
+
+    - name: Remove instance-local binary links
+      ansible.builtin.file:
+        path: "{{ mysql_install_dir }}"
+        state: absent
+
+    - name: Remove the instance data and log tree
+      ansible.builtin.file:
+        path: "{{ mysql_base_dir }}"
+        state: absent
+
+    - name: Remove the instance runtime directory
+      ansible.builtin.file:
+        path: "{{ mysql_run_dir }}"
+        state: absent
+
+    - name: Confirm the instance artifacts are gone
+      ansible.builtin.stat:
+        path: "{{ item }}"
+      loop:
+        - "{{ mysql_config_file }}"
+        - "{{ mysql_install_dir }}"
+        - "{{ mysql_base_dir }}"
+        - "{{ mysql_run_dir }}"
+      register: mysql_rollback_artifacts
+
+    - name: Assert that all instance artifacts are gone
+      ansible.builtin.assert:
+        that:
+          - mysql_rollback_artifacts.results | selectattr('stat.exists') | list | length == 0
+        fail_msg: "One or more MySQL delivery artifacts remain after rollback"
+        quiet: true