feat: add checksummed database migrations

tests/integration/__init__.py

@@ -0,0 +1 @@
+"""PostgreSQL-backed integration tests."""

tests/integration/test_migrations.py

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+"""PostgreSQL migration acceptance checks."""
+
+import os
+import uuid
+
+import asyncpg  # type: ignore[import-untyped]
+import pytest
+
+from app.db.migrations import migrate
+
+pytestmark = [
+    pytest.mark.integration,
+    pytest.mark.skipif(not os.getenv("TEST_DATABASE_URL"), reason="TEST_DATABASE_URL is required"),
+]
+
+
+async def test_migration_is_repeatable_and_constraints_hold() -> None:
+    connection = await asyncpg.connect(os.environ["TEST_DATABASE_URL"])
+    try:
+        await migrate(connection)
+        assert await migrate(connection) == 0
+        node_id = uuid.uuid4()
+        await connection.execute(
+            "INSERT INTO nodes(id, name, status) VALUES($1, $2, 'online') ON CONFLICT DO NOTHING",
+            node_id,
+            f"test-{node_id}",
+        )
+        with pytest.raises(asyncpg.CheckViolationError):
+            async with connection.transaction():
+                await connection.execute(
+                    "INSERT INTO nodes(id, name, status) VALUES($1, $2, 'invalid')",
+                    uuid.uuid4(),
+                    f"invalid-{node_id}",
+                )
+    finally:
+        await connection.close()