feat(poll): reorder options without invalidating answers

src/govoplan_poll/backend/service.py

@@ -1382,6 +1382,61 @@ def update_poll_option(
     return option
 
 
+def reorder_poll_options(
+    session: Session,
+    *,
+    tenant_id: str,
+    poll_id: str,
+    option_ids: tuple[str, ...],
+    mutation_owner: PollMutationOwner | None = None,
+) -> Poll:
+    """Atomically replace the complete active option order.
+
+    Position is presentation state, so existing answers remain attached to
+    their stable option identities. The Poll row is locked first to keep the
+    lock order consistent with response and option mutations.
+    """
+
+    poll = _lock_poll_for_response(
+        session,
+        tenant_id=tenant_id,
+        poll_id=poll_id,
+    )
+    _assert_poll_mutation_owner(poll, mutation_owner=mutation_owner)
+    requested_ids = tuple(option_ids)
+    if len(requested_ids) != len(set(requested_ids)):
+        raise PollError("Poll option order cannot contain duplicate options")
+    options = (
+        session.query(PollOption)
+        .filter(
+            PollOption.tenant_id == tenant_id,
+            PollOption.poll_id == poll.id,
+            PollOption.deleted_at.is_(None),
+        )
+        .order_by(PollOption.id.asc())
+        .populate_existing()
+        .with_for_update()
+        .all()
+    )
+    by_id = {option.id: option for option in options}
+    if set(requested_ids) != set(by_id):
+        raise PollError(
+            "Poll option order must contain every active option exactly once"
+        )
+    current_ids = tuple(
+        option.id
+        for option in sorted(options, key=lambda item: (item.position, item.id))
+    )
+    if requested_ids == current_ids:
+        return poll
+    if poll.status not in {"draft", "open"}:
+        raise PollError("Only draft or open poll options can be reordered")
+    for position, option_id in enumerate(requested_ids):
+        by_id[option_id].position = position
+    session.flush()
+    return poll
+
+
 def _locked_active_poll_responses(session: Session, *, poll: Poll) -> list[PollResponse]:
     return (
         session.query(PollResponse)