diff --git a/roles/web-app-matrix/tasks/flavor/ansible/05_proxy_wiring.yml b/roles/web-app-matrix/tasks/flavor/ansible/05_proxy_wiring.yml
index 48390e8be2..5645763917 100644
--- a/roles/web-app-matrix/tasks/flavor/ansible/05_proxy_wiring.yml
+++ b/roles/web-app-matrix/tasks/flavor/ansible/05_proxy_wiring.yml
@@ -183,16 +183,6 @@
     http_port: "{{ MATRIX_SYNAPSE_PORT }}"
     proxy_internal_port: "{{ MATRIX_SYNAPSE_CONTAINER_PORT }}"
 
-- name: "🔀 front-proxy: Synapse federation listener and Matrix RTC paths"
-  stack_host_template:
-    src: "flavor/ansible/synapse.conf.j2"
-    dest: "{{ lookup('nginx', 'files.domain', MATRIX_SYNAPSE_DOMAIN) }}"
-  vars:
-    domain: "{{ MATRIX_SYNAPSE_DOMAIN }}"
-    http_port: "{{ MATRIX_SYNAPSE_PORT }}"
-    proxy_internal_port: "{{ MATRIX_SYNAPSE_CONTAINER_PORT }}"
-  notify: restart-openresty
-
 - name: "🔀 front-proxy: federation delegation"
   ansible.builtin.include_tasks: "{{ role_path }}/tasks/utils/well_known.yml"
 
diff --git a/roles/web-app-matrix/templates/proxy.conf.j2 b/roles/web-app-matrix/templates/proxy.conf.j2
index 36a1c0abd3..1f10f608a2 100644
--- a/roles/web-app-matrix/templates/proxy.conf.j2
+++ b/roles/web-app-matrix/templates/proxy.conf.j2
@@ -1,4 +1,6 @@
-{% if domain == MATRIX_SYNAPSE_DOMAIN %}
+{% if domain == MATRIX_SYNAPSE_DOMAIN and matrix_flavor == 'ansible' %}
+{% include 'roles/web-app-matrix/templates/flavor/ansible/synapse.conf.j2' %}
+{% elif domain == MATRIX_SYNAPSE_DOMAIN %}
 {% include 'roles/web-app-matrix/templates/synapse.conf.j2' %}
 {% else %}
 {% include 'roles/sys-svc-proxy/templates/vhost/basic.conf.j2' %}
diff --git a/tests/unit/python/roles/web-app-matrix/test_synapse_vhost_single_writer.py b/tests/unit/python/roles/web-app-matrix/test_synapse_vhost_single_writer.py
new file mode 100644
index 0000000000..d4062e84c3
--- /dev/null
+++ b/tests/unit/python/roles/web-app-matrix/test_synapse_vhost_single_writer.py
@@ -0,0 +1,91 @@
+from __future__ import annotations
+
+import unittest
+
+from jinja2 import (
+    ChoiceLoader,
+    DictLoader,
+    Environment,
+    FileSystemLoader,
+    StrictUndefined,
+)
+
+from utils.cache.files import PROJECT_ROOT, read_text
+
+PROXY_TEMPLATE = "roles/web-app-matrix/templates/proxy.conf.j2"
+TASKS_DIR = PROJECT_ROOT / "roles/web-app-matrix/tasks"
+SYNAPSE_VHOST_DEST = "lookup('nginx', 'files.domain', MATRIX_SYNAPSE_DOMAIN)"
+
+STUBS = {
+    "roles/web-app-matrix/templates/flavor/ansible/synapse.conf.j2": "ANSIBLE_SYNAPSE",
+    "roles/web-app-matrix/templates/synapse.conf.j2": "COMPOSE_SYNAPSE",
+    "roles/sys-svc-proxy/templates/vhost/basic.conf.j2": "BASIC",
+}
+
+SYNAPSE_DOMAIN = "matrix.example.test"
+
+
+def _render(*, domain: str, flavor: str) -> str:
+    """Render the front-proxy template of web-app-matrix with stubbed includes.
+
+    Args:
+        domain: vhost domain the front proxy renders.
+        flavor: value of the matrix_flavor fact.
+
+    Returns:
+        The rendered marker of the included vhost template.
+    """
+    env = Environment(
+        autoescape=True,
+        undefined=StrictUndefined,
+        loader=ChoiceLoader([DictLoader(STUBS), FileSystemLoader(str(PROJECT_ROOT))]),
+    )
+    return (
+        env.get_template(PROXY_TEMPLATE)
+        .render(
+            domain=domain,
+            matrix_flavor=flavor,
+            MATRIX_SYNAPSE_DOMAIN=SYNAPSE_DOMAIN,
+        )
+        .strip()
+    )
+
+
+class TestSynapseVhostSingleWriter(unittest.TestCase):
+    def test_ansible_flavor_front_proxy_renders_the_ansible_synapse_vhost(
+        self,
+    ) -> None:
+        self.assertEqual(
+            _render(domain=SYNAPSE_DOMAIN, flavor="ansible"), "ANSIBLE_SYNAPSE"
+        )
+
+    def test_compose_flavor_front_proxy_renders_the_compose_synapse_vhost(
+        self,
+    ) -> None:
+        self.assertEqual(
+            _render(domain=SYNAPSE_DOMAIN, flavor="compose"), "COMPOSE_SYNAPSE"
+        )
+
+    def test_other_domains_render_the_basic_vhost(self) -> None:
+        for flavor in ("ansible", "compose"):
+            with self.subTest(flavor=flavor):
+                self.assertEqual(
+                    _render(domain="element.example.test", flavor=flavor), "BASIC"
+                )
+
+    def test_no_matrix_task_rewrites_the_front_proxy_synapse_vhost(self) -> None:
+        writers = [
+            str(path.relative_to(PROJECT_ROOT))
+            for path in sorted(TASKS_DIR.rglob("*.yml"))
+            if SYNAPSE_VHOST_DEST in read_text(str(path))
+        ]
+        self.assertEqual(
+            writers,
+            [],
+            "sys-stk-front-proxy owns the Synapse vhost; a second writer flips "
+            "its content every deploy and forces an OpenResty redeploy",
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()