diff --git a/tests/mattermost-lts/ops.py b/tests/mattermost-lts/ops.py
new file mode 100644
index 0000000..1f33c85
--- /dev/null
+++ b/tests/mattermost-lts/ops.py
@@ -0,0 +1,46 @@
+"""mattermost-lts — pre-op seed hooks (Phase 1e HC3). The orchestrator runs these BEFORE each op; the
+matching test_<op>.py asserts post-op (assertion-only). The marker is a dedicated `ci_marker` row in
+postgres (mattermost's own schema migrations don't touch it), written via psql in the `db` service
+(POSTGRES_USER=mattermost, POSTGRES_DB=mattermost, password /run/secrets/postgres_password). The
+recipe's `db` service is backupbot-labelled (pg_dump pre-hook + the whole PGDATA dir at
+backup.path=/var/lib/postgresql/data/), so the marker rides the backup→restore cycle."""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
+
+def _psql(domain, sql):
+    cmd = (
+        "PGPASSWORD=$(cat /run/secrets/postgres_password) "
+        f'psql -U mattermost -d mattermost -tAc "{sql}"'
+    )
+    return lifecycle.exec_in_app(domain, ["sh", "-c", cmd], service="db").strip()
+
+
+def _seed(domain, value):
+    _psql(
+        domain,
+        "CREATE TABLE IF NOT EXISTS ci_marker(v text); DELETE FROM ci_marker; "
+        f"INSERT INTO ci_marker VALUES('{value}');",
+    )
+    assert _psql(domain, "SELECT v FROM ci_marker;") == value
+
+
+def pre_upgrade(domain, meta):
+    _seed(domain, "upgrade-survives")
+
+
+def pre_backup(domain, meta):
+    _seed(domain, "original")
+
+
+def pre_restore(domain, meta):
+    # drop the marker table (diverge from the backup) so a successful restore is observable
+    _psql(domain, "DROP TABLE ci_marker;")
+    assert _psql(domain, "SELECT to_regclass('public.ci_marker');") in (
+        "",
+        "NULL",
+    ), "drop did not take"
diff --git a/tests/mattermost-lts/test_backup.py b/tests/mattermost-lts/test_backup.py
new file mode 100644
index 0000000..30b0716
--- /dev/null
+++ b/tests/mattermost-lts/test_backup.py
@@ -0,0 +1,23 @@
+"""mattermost-lts — BACKUP overlay (Phase 1e HC3): assertion-only + additive.
+ops.pre_backup wrote "original" into postgres before the backup op (the recipe's db pre-hook dumps
+the DB + archives the PGDATA dir). This overlay ADDS: the seeded row is intact at backup time."""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
+
+def _psql(domain, sql):
+    cmd = (
+        "PGPASSWORD=$(cat /run/secrets/postgres_password) "
+        f'psql -U mattermost -d mattermost -tAc "{sql}"'
+    )
+    return lifecycle.exec_in_app(domain, ["sh", "-c", cmd], service="db").strip()
+
+
+def test_backup_captures_state(live_app):
+    assert (
+        _psql(live_app, "SELECT v FROM ci_marker;") == "original"
+    ), "the seeded postgres state was not present at backup time"
diff --git a/tests/mattermost-lts/test_install.py b/tests/mattermost-lts/test_install.py
new file mode 100644
index 0000000..fd73f9b
--- /dev/null
+++ b/tests/mattermost-lts/test_install.py
@@ -0,0 +1,20 @@
+"""mattermost-lts — INSTALL overlay (Phase 1d, DG4): override + extend-by-composition.
+Reuses the generic "really serving" assertion, then ADDS a recipe-specific check: mattermost's REST
+liveness endpoint /api/v4/system/ping answers 200 over real HTTPS through Traefik (proves the app +
+its DB-backed API are up, not just a proxy 200). Assertion-only on the shared deployment."""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import generic, lifecycle  # noqa: E402
+
+
+def test_serving_and_api(live_app, meta):
+    # extend-by-composition: reuse the generic "really serving" assertion first ...
+    generic.assert_serving(live_app, meta)
+    # ... then the recipe-specific assertion: the mattermost REST liveness endpoint answers 200.
+    status = lifecycle.http_get(live_app, "/api/v4/system/ping")
+    assert status == 200, (
+        f"expected 200 from {live_app}/api/v4/system/ping, got {status}"
+    )
diff --git a/tests/mattermost-lts/test_restore.py b/tests/mattermost-lts/test_restore.py
new file mode 100644
index 0000000..c537a59
--- /dev/null
+++ b/tests/mattermost-lts/test_restore.py
@@ -0,0 +1,24 @@
+"""mattermost-lts — RESTORE overlay (Phase 1e HC3): data-integrity, assertion-only + additive.
+ops.pre_restore dropped the marker table (diverge); the orchestrator restored once (the recipe's db
+backup is the whole PGDATA dir). This overlay ADDS: the restored DB matches the pre-mutation
+"original". Read via psql in the `db` service."""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
+
+def _psql(domain, sql):
+    cmd = (
+        "PGPASSWORD=$(cat /run/secrets/postgres_password) "
+        f'psql -U mattermost -d mattermost -tAc "{sql}"'
+    )
+    return lifecycle.exec_in_app(domain, ["sh", "-c", cmd], service="db").strip()
+
+
+def test_restore_returns_state(live_app):
+    assert (
+        _psql(live_app, "SELECT v FROM ci_marker;") == "original"
+    ), "restore did not return the pre-mutation postgres state"
diff --git a/tests/mattermost-lts/test_upgrade.py b/tests/mattermost-lts/test_upgrade.py
new file mode 100644
index 0000000..ab26c93
--- /dev/null
+++ b/tests/mattermost-lts/test_upgrade.py
@@ -0,0 +1,23 @@
+"""mattermost-lts — UPGRADE overlay (Phase 1e HC3): data-continuity, assertion-only + additive.
+ops.pre_upgrade wrote a postgres marker row before the upgrade; this overlay ADDS: the postgres data
+survived the chaos crossover. Read via psql in the `db` service."""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
+
+def _psql(domain, sql):
+    cmd = (
+        "PGPASSWORD=$(cat /run/secrets/postgres_password) "
+        f'psql -U mattermost -d mattermost -tAc "{sql}"'
+    )
+    return lifecycle.exec_in_app(domain, ["sh", "-c", cmd], service="db").strip()
+
+
+def test_upgrade_preserves_data(live_app):
+    assert (
+        _psql(live_app, "SELECT v FROM ci_marker;") == "upgrade-survives"
+    ), "postgres data did not survive the upgrade"