feat(2): enroll mattermost-lts (Q4.5) — recipe_meta (HTTP-native, self-contained postgres) + health_check (root + /api/v4/system/ping) + PARITY (no corpus → P2 vacuous; create-message §4.3 + P4 ops planned)

tests/mattermost-lts/functional/test_health_check.py

@@ -0,0 +1,37 @@
+"""mattermost-lts — Phase-2 health_check (recipe-maintainer corpus has no parity test for this recipe).
+
+Two real assertions on app state, not a bare root 200:
+  1. The web app is served at `/` (200/302 — SPA shell or redirect toward login).
+  2. The dedicated API liveness endpoint GET /api/v4/system/ping returns {"status":"OK"} — this
+     proves the mattermost server process (not just Traefik) is up and its API router is live.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "..", "runner"))
+from harness import http as harness_http  # noqa: E402
+
+
+def test_root_serves(live_app):
+    """GET / → 200 or 302 (mattermost web app shell / login redirect)."""
+    url = f"https://{live_app}/"
+    status, _ = harness_http.retry_http_get(
+        url, expect_status=(200, 302), max_wait=60, interval=3
+    )
+    assert status in (200, 302), f"GET {url} HTTP {status} (expected 200/302)"
+
+
+def test_system_ping_ok(live_app):
+    """GET /api/v4/system/ping → 200 with JSON {"status":"OK"} — the mattermost server's own
+    liveness endpoint (distinguishes a live mattermost API from a Traefik fallback / dead backend)."""
+    url = f"https://{live_app}/api/v4/system/ping"
+    status, body = harness_http.retry_http_get(
+        url, expect_status=200, max_wait=120, interval=3
+    )
+    assert status == 200, f"GET {url} HTTP {status} (expected 200)"
+    assert isinstance(body, dict) and body.get("status") == "OK", (
+        f"/api/v4/system/ping did not report status=OK; got {body!r}"
+    )