Mark matrix_client_cinny_path_prefix as not supported anymore

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3701

We can restore support for it by making a non-/ path prefix trigger a
self-build with a modified build config, so that a Cinny version with
path-prefix support would be produced. Traefik label changes may also be
required.

For now, we're not doing all that work, but simply dropping support for path
prefixes for Cinny.

docs/configuring-playbook-client-cinny.md

@@ -16,27 +16,25 @@ matrix_client_cinny_enabled: true
 
 By default, this playbook installs Cinny on the `cinny.` subdomain (`cinny.example.com`) and requires you to [adjust your DNS records](#adjusting-dns-records).
 
-By tweaking the `matrix_client_cinny_hostname` and `matrix_client_cinny_path_prefix` variables, you can easily make the service available at a **different hostname and/or path** than the default one.
+By tweaking the `matrix_client_cinny_hostname` variable, you can easily make the service available at a **different hostname** than the default one.
+
+While a `matrix_client_cinny_path_prefix` variable exists for tweaking the path-prefix, it's [not supported anymore](https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3701), because Cinny requires an application rebuild (with a tweaked build config) to be functional under a custom path.
 
 Example additional configuration for your `inventory/host_vars/matrix.example.com/vars.yml` file:
 
 ```yaml
-# Switch to the domain used for Matrix services (`matrix.example.com`),
-# so we won't need to add additional DNS records for Cinny.
-matrix_client_cinny_hostname: "{{ matrix_server_fqn_matrix }}"
-
-# Expose under the /cinny subpath
-matrix_client_cinny_path_prefix: /cinny
+# Switch to a different domain (`app.example.com`) than the default one (`cinny.example.com`)
+matrix_client_cinny_hostname: "app.{{ matrix_domain }}"
 ```
 
 ## Adjusting DNS records
 
-Once you've decided on the domain and path, **you may need to adjust your DNS** records to point the Cinny domain to the Matrix server.
+Once you've decided on the domain, **you may need to adjust your DNS** records to point the Cinny domain to the Matrix server.
 
 By default, you will need to create a CNAME record for `cinny`. See [Configuring DNS](configuring-dns.md) for details about DNS changes.
 
-If you've decided to reuse the `matrix.` domain, you won't need to do any extra DNS configuration.
+If you've adjusted `matrix_client_cinny_hostname`, you will need to adjust your DNS configuration accordingly.
 
 ## Installing
 
-After configuring the playbook and potentially [adjusting your DNS records](#adjusting-dns-records), run the [installation](installing.md) command: `just install-all` or `just setup-all`
+After configuring the playbook and [adjusting your DNS records](#adjusting-dns-records), run the [installation](installing.md) command: `just install-all` or `just setup-all`

roles/custom/matrix-client-cinny/tasks/validate_config.yml

@@ -8,6 +8,14 @@
     - matrix_client_cinny_default_hs_url
     - matrix_client_cinny_container_network
 
+- name: Fail if matrix_client_cinny_path_prefix is not /
+  ansible.builtin.fail:
+    msg: >-
+      `matrix_client_cinny_path_prefix` is set to `{{ matrix_client_cinny_path_prefix }}` in your configuration, but Cinny no longer supports hosting under a path prefix without an application rebuild.
+      Consider removing your `matrix_client_cinny_path_prefix` override and adjusting the Cinny hostname via `matrix_server_fqn_cinny` or `matrix_client_cinny_hostname`.
+      See https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3701
+  when: "matrix_client_cinny_path_prefix != '/'"
+
 - when: matrix_client_cinny_container_labels_traefik_enabled | bool
   block:
     - name: Fail if required matrix-client-cinny Traefik settings not defined