diff --git a/tests/plausible/ops.py b/tests/plausible/ops.py
new file mode 100644
index 0000000..010db93
--- /dev/null
+++ b/tests/plausible/ops.py
@@ -0,0 +1,37 @@
+"""plausible — pre-op seed hooks (Phase 1e HC3). Marker is a `ci_marker` row in the metadata postgres
+(`db` service; POSTGRES_USER/DB/PASSWORD are plausible/plausible/plausible, read from the container's
+own env). plausible's recipe backs up postgres via a real pg_dump hook (backupbot pre-hook pg_dump -Fc
+| gzip; restore post-hook pg_restore --clean), so the marker survives backup→restore."""
+
+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 = f'PGPASSWORD="$POSTGRES_PASSWORD" psql -U "$POSTGRES_USER" -d "$POSTGRES_DB" -tAc "{sql}"'
+    return lifecycle.exec_in_app(domain, ["sh", "-c", cmd], service="db").strip()
+
+
+def _seed(domain, value):
+    _psql(
+        domain,
+        "CREATE TABLE IF NOT EXISTS ci_marker(v text); DELETE FROM ci_marker; "
+        f"INSERT INTO ci_marker VALUES('{value}');",
+    )
+    assert _psql(domain, "SELECT v FROM ci_marker;") == value
+
+
+def pre_upgrade(domain, meta):
+    _seed(domain, "upgrade-survives")
+
+
+def pre_backup(domain, meta):
+    _seed(domain, "original")
+
+
+def pre_restore(domain, meta):
+    _psql(domain, "DROP TABLE ci_marker;")
+    assert _psql(domain, "SELECT to_regclass('public.ci_marker');") in ("", "NULL"), "drop did not take"
diff --git a/tests/plausible/test_backup.py b/tests/plausible/test_backup.py
new file mode 100644
index 0000000..b3c7336
--- /dev/null
+++ b/tests/plausible/test_backup.py
@@ -0,0 +1,17 @@
+"""plausible — BACKUP overlay (Phase 1e HC3): data-integrity, assertion-only. Reads the postgres
+ci_marker via psql in the `db` service (plausible's metadata DB; pg_dump backup hook)."""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
+
+def _psql(domain, sql):
+    cmd = f'PGPASSWORD="$POSTGRES_PASSWORD" psql -U "$POSTGRES_USER" -d "$POSTGRES_DB" -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", "seeded postgres state not present at backup time"
diff --git a/tests/plausible/test_install.py b/tests/plausible/test_install.py
new file mode 100644
index 0000000..3fe3e06
--- /dev/null
+++ b/tests/plausible/test_install.py
@@ -0,0 +1,13 @@
+"""plausible — INSTALL overlay (Phase 1d): reuse generic serving, then assert the SPA shell serves."""
+
+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(live_app, meta):
+    generic.assert_serving(live_app, meta)
+    status = lifecycle.http_get(live_app, "/")
+    assert status in (200, 301, 302), f"expected 2xx/3xx from {live_app}, got {status}"
diff --git a/tests/plausible/test_restore.py b/tests/plausible/test_restore.py
new file mode 100644
index 0000000..5fc0d99
--- /dev/null
+++ b/tests/plausible/test_restore.py
@@ -0,0 +1,17 @@
+"""plausible — RESTORE overlay (Phase 1e HC3): data-integrity, assertion-only. Reads the postgres
+ci_marker via psql in the `db` service (plausible's metadata DB; pg_dump backup hook)."""
+
+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 = f'PGPASSWORD="$POSTGRES_PASSWORD" psql -U "$POSTGRES_USER" -d "$POSTGRES_DB" -tAc "{sql}"'
+    return lifecycle.exec_in_app(domain, ["sh", "-c", cmd], service="db").strip()
+
+
+def test_restore_returns_state(live_app):
+    assert _psql(live_app, "SELECT v FROM ci_marker;") == "original", "restore did not return the pre-mutation postgres state"
diff --git a/tests/plausible/test_upgrade.py b/tests/plausible/test_upgrade.py
new file mode 100644
index 0000000..cbdb872
--- /dev/null
+++ b/tests/plausible/test_upgrade.py
@@ -0,0 +1,17 @@
+"""plausible — UPGRADE overlay (Phase 1e HC3): data-integrity, assertion-only. Reads the postgres
+ci_marker via psql in the `db` service (plausible's metadata DB; pg_dump backup hook)."""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
+
+def _psql(domain, sql):
+    cmd = f'PGPASSWORD="$POSTGRES_PASSWORD" psql -U "$POSTGRES_USER" -d "$POSTGRES_DB" -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"