diff --git a/testing/tests/test_hermes_public_host_continuity.py b/testing/tests/test_hermes_public_host_continuity.py
new file mode 100644
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--- /dev/null
+++ b/testing/tests/test_hermes_public_host_continuity.py
@@ -0,0 +1,153 @@
+"""Public chat/triage hostnames stay served on every layer during a rename.
+
+PR #34 renamed the chat and triage public hosts in place: the legacy names left
+the certificate SANs, the Ingress rules, the CoreDNS overrides and the Keycloak
+ensure script in one change. The legacy hosts began answering 404 with Traefik's
+default certificate while the renamed hosts could not finish a login, because
+Keycloak matches ``redirect_uri`` exactly and still held the old callback. Chat
+and triage were unreachable on every hostname at once.
+
+These tests pin the contract that makes that outage impossible to reintroduce
+silently: a public host is either served by all four layers or by none of them.
+"""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+import pytest
+import yaml
+
+REPO = Path(__file__).parents[2]
+HERMES = REPO / "services/hermes"
+KEYCLOAK = REPO / "services/keycloak"
+COREDNS = REPO / "infrastructure/core/coredns-custom.yaml"
+ENSURE_SCRIPT = KEYCLOAK / "scripts/hermes_access_oidc_ensure.sh"
+
+# Every hostname the chat/triage surfaces must answer on, with the oauth2-proxy
+# backend that serves it. Both the renamed and the legacy names belong here
+# until a deliberate retirement change removes a row from this table.
+PUBLIC_HOSTS = {
+    "chat.bstein.dev": "oauth2-proxy-hermes-chat",
+    "chat.hermes.bstein.dev": "oauth2-proxy-hermes-chat",
+    "triage.bstein.dev": "oauth2-proxy-hermes-triage",
+    "triage.hermes.bstein.dev": "oauth2-proxy-hermes-triage",
+}
+
+# The agent surface was deliberately untouched by the rename.
+AGENT_HOST = "agent.hermes.bstein.dev"
+
+
+def _docs(path: Path) -> list[dict]:
+    return [doc for doc in yaml.safe_load_all(path.read_text()) if doc]
+
+
+def _named(path: Path, kind: str, name: str) -> dict:
+    for doc in _docs(path):
+        if doc.get("kind") == kind and doc["metadata"]["name"] == name:
+            return doc
+    raise AssertionError(f"{kind}/{name} missing from {path}")
+
+
+@pytest.fixture(scope="module")
+def certificate() -> dict:
+    return _named(HERMES / "agent-certificate.yaml", "Certificate", "hermes-sites-tls")
+
+
+@pytest.fixture(scope="module")
+def sites_ingress() -> dict:
+    return _named(HERMES / "agent-ingress.yaml", "Ingress", "hermes-sites")
+
+
+@pytest.fixture(scope="module")
+def coredns_hosts() -> set[str]:
+    block = yaml.safe_load(COREDNS.read_text())["data"]["bstein-dev.server"]
+    return {
+        line.split()[1]
+        for line in block.splitlines()
+        if len(line.split()) == 2 and re.fullmatch(r"[\d.]+", line.split()[0])
+    }
+
+
+@pytest.fixture(scope="module")
+def ensure_script() -> str:
+    return ENSURE_SCRIPT.read_text()
+
+
+@pytest.mark.parametrize("host", sorted(PUBLIC_HOSTS))
+def test_host_is_on_the_shared_certificate(host: str, certificate: dict):
+    """A host without a SAN serves Traefik's default self-signed certificate."""
+    assert host in certificate["spec"]["dnsNames"]
+
+
+@pytest.mark.parametrize("host", sorted(PUBLIC_HOSTS))
+def test_host_resolves_inside_the_cluster(host: str, coredns_hosts: set[str]):
+    assert host in coredns_hosts
+
+
+@pytest.mark.parametrize("host", sorted(PUBLIC_HOSTS))
+def test_host_has_an_ingress_rule_and_tls_entry(host: str, sites_ingress: dict):
+    """A host without a rule answers 404 even though DNS and TLS look healthy."""
+    spec = sites_ingress["spec"]
+    assert host in {name for entry in spec["tls"] for name in entry["hosts"]}
+
+    rule = next((item for item in spec["rules"] if item["host"] == host), None)
+    assert rule is not None, f"no hermes-sites rule serves {host}"
+
+    backends = {
+        path["backend"]["service"]["name"] for path in rule["http"]["paths"]
+    }
+    assert backends == {PUBLIC_HOSTS[host]}
+
+
+@pytest.mark.parametrize("host", sorted(PUBLIC_HOSTS))
+def test_host_is_registered_with_keycloak(host: str, ensure_script: str):
+    """Keycloak matches redirect_uri exactly, so every served host needs one."""
+    assert f"https://{host}" in ensure_script
+
+
+def test_agent_surface_was_not_touched_by_the_rename(
+    certificate: dict, coredns_hosts: set[str], ensure_script: str
+):
+    assert AGENT_HOST in certificate["spec"]["dnsNames"]
+    assert AGENT_HOST in coredns_hosts
+    assert f"https://{AGENT_HOST}" in ensure_script
+
+
+def test_ensure_script_registers_legacy_and_renamed_origins_together(
+    ensure_script: str,
+):
+    """The renamed proxies must carry both origins; the agent proxy only one."""
+    for client, canonical, legacy in (
+        ("hermes-chat-proxy", "chat.bstein.dev", "chat.hermes.bstein.dev"),
+        ("hermes-triage-proxy", "triage.bstein.dev", "triage.hermes.bstein.dev"),
+    ):
+        call = re.search(
+            rf'ensure_proxy_client "{client}".*?(?=\nensure_)',
+            ensure_script,
+            re.DOTALL,
+        )
+        assert call, f"{client} is never ensured"
+        assert f"https://{canonical}" in call.group(0)
+        assert f"https://{legacy}" in call.group(0)
+
+
+def test_ensure_job_is_rerun_whenever_the_script_changes():
+    """The Job is immutable, so a stale name silently skips the rerun."""
+    job = _named(
+        KEYCLOAK / "bootstrap-jobs/hermes-access-oidc-client-job.yaml",
+        "Job",
+        # The suffix moves with every rerun; resolve it from the manifest.
+        _job_name(),
+    )
+    assert job["spec"]["template"]["spec"]["containers"][0]["command"] == [
+        "/scripts/hermes_access_oidc_ensure.sh"
+    ]
+
+
+def _job_name() -> str:
+    path = KEYCLOAK / "bootstrap-jobs/hermes-access-oidc-client-job.yaml"
+    name = yaml.safe_load(path.read_text())["metadata"]["name"]
+    assert re.fullmatch(r"hermes-access-oidc-client-ensure-\d+", name), name
+    return name