feat(fc2c-i): migration 0004 enables tsm_system_rows

tests/test_migration_0004.py

@@ -0,0 +1,27 @@
+"""Integration: the tsm_system_rows extension is installed by migration 0004.
+
+Needs a real Postgres (CI does not provision one), so integration-marked.
+"""
+
+import pytest
+from sqlalchemy import text
+
+pytestmark = pytest.mark.integration
+
+
+@pytest.mark.asyncio
+async def test_tsm_system_rows_extension_present(db):
+    row = (
+        await db.execute(
+            text("SELECT 1 FROM pg_extension WHERE extname = 'tsm_system_rows'")
+        )
+    ).first()
+    assert row is not None
+
+
+@pytest.mark.asyncio
+async def test_system_rows_sampling_is_usable(db):
+    # Should parse and execute even on an empty table.
+    await db.execute(
+        text("SELECT * FROM image_record TABLESAMPLE SYSTEM_ROWS(1)")
+    )