diff --git a/src/govoplan_core/core/poll.py b/src/govoplan_core/core/poll.py
index 9918dc4..d394e28 100644
--- a/src/govoplan_core/core/poll.py
+++ b/src/govoplan_core/core/poll.py
@@ -58,6 +58,21 @@ class PollUpdateCommand:
     closes_at: datetime | None
 
 
+@dataclass(frozen=True, slots=True)
+class PollOptionUpdateCommand:
+    """Complete mutable option snapshot supplied by an owning module.
+
+    Providers must treat an exact repeat as a no-op.  When the snapshot
+    changes, answers for this option are invalidated while answers for other
+    options are retained.
+    """
+
+    label: str
+    description: str | None = None
+    value: Mapping[str, object] | None = None
+    metadata: Mapping[str, object] = field(default_factory=dict)
+
+
 @dataclass(frozen=True, slots=True)
 class PollInvitationCommand:
     respondent_id: str | None = None
@@ -102,6 +117,14 @@ class PollInvitationRef:
     token: str
 
 
+@dataclass(frozen=True, slots=True)
+class PollAnswerRef:
+    option_id: str | None = None
+    option_key: str | None = None
+    value: object = None
+    rank: int | None = None
+
+
 @dataclass(frozen=True, slots=True)
 class PollResponseRef:
     invitation_id: str | None
@@ -110,6 +133,9 @@ class PollResponseRef:
     # consumer can use it to reconcile an authenticated response without
     # trusting client-supplied invitation metadata.
     respondent_id: str | None = None
+    # Optional for backwards compatibility.  Providers that support response
+    # editing expose the authoritative, still-valid answers here.
+    answers: tuple[PollAnswerRef, ...] = ()
 
 
 @runtime_checkable
@@ -144,6 +170,19 @@ class PollSchedulingProvider(Protocol):
     ) -> PollRef:
         ...
 
+    def update_option(
+        self,
+        session: object,
+        *,
+        tenant_id: str,
+        poll_id: str,
+        option_id: str,
+        command: PollOptionUpdateCommand,
+    ) -> PollOptionRef:
+        """Update one option and invalidate only answers for that option."""
+
+        ...
+
     def open_poll(self, session: object, *, tenant_id: str, poll_id: str) -> PollRef:
         ...
 
diff --git a/tests/test_poll_contract.py b/tests/test_poll_contract.py
new file mode 100644
index 0000000..af7fe49
--- /dev/null
+++ b/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()