Api Limit Policies List Update

Minimal pre-enrichment serializer for the /list/ route.

DataEnrichmentMixin.list() serializes the page once with the view's serializer_class before enrich_results rebuilds each row from scratch (one PG IN-refetch + one pipelined Redis HGET + one TagManager IN-query for the whole page). If we used the full LimitPolicyListSerializer for that first pass, every row's current_state SerializerMethodField would fire a Redis HGET and every tags SerializerMethodField would fire a TagManager query — N+1 work that enrich_results immediately discards.

This serializer emits only id because that is all LimitPoliciesListView.enrich_results reads off the dict (policy_ids = [row.get("id") for row in results …]). The OpenAPI response contract is declared via @extend_schema( responses=LimitPolicyStateRowSerializer) on the view, so codegen types still reflect the merged shape.