feat(poll): extend response editing contract

tests/test_poll_contract.py

@@ -0,0 +1,36 @@
+from __future__ import annotations
+
+import unittest
+from datetime import datetime, timezone
+
+from govoplan_core.core.poll import PollAnswerRef, PollOptionUpdateCommand, PollResponseRef
+
+
+class PollContractTests(unittest.TestCase):
+    def test_response_ref_remains_backwards_compatible_and_can_carry_answers(self) -> None:
+        submitted_at = datetime(2026, 7, 20, tzinfo=timezone.utc)
+
+        legacy = PollResponseRef(None, submitted_at)
+        detailed = PollResponseRef(
+            invitation_id="invitation-1",
+            submitted_at=submitted_at,
+            respondent_id="person-1",
+            answers=(PollAnswerRef(option_id="option-1", option_key="slot-1", value="available"),),
+        )
+
+        self.assertEqual(legacy.answers, ())
+        self.assertEqual(detailed.answers[0].value, "available")
+
+    def test_option_update_command_is_a_complete_immutable_snapshot(self) -> None:
+        command = PollOptionUpdateCommand(
+            label="Tuesday 10:00",
+            value={"slot_id": "slot-1"},
+            metadata={"source": "scheduling"},
+        )
+
+        self.assertEqual(command.label, "Tuesday 10:00")
+        self.assertEqual(command.value, {"slot_id": "slot-1"})
+
+
+if __name__ == "__main__":
+    unittest.main()