perf(question-feed): memoize contested-card lookups within a single feed request

MPCAutofill/cardpicker/question_feed.py

@@ -473,6 +473,8 @@ def _tier_2_contested(
     answered_artist_card_ids: Optional[set[int]] = None,
     answered_tag_card_ids_by_tag: Optional[dict[str, set[int]]] = None,
     not_official_art_card_ids: Optional[set[int]] = None,
+    contested_card_ids: Optional[list[int]] = None,
+    contested_artist_card_ids: Optional[list[int]] = None,
 ) -> Optional[tuple[QuestionFeedItem, str]]:
     if answered_card_ids is None:
         answered_card_ids = _voter_answered_printing_card_ids(anonymous_id)
@@ -482,9 +484,13 @@ def _tier_2_contested(
         answered_tag_card_ids_by_tag = _voter_answered_tag_card_ids_by_tag(anonymous_id)
     if not_official_art_card_ids is None:
         not_official_art_card_ids = _not_official_art_card_ids()
+    if contested_card_ids is None:
+        contested_card_ids = get_contested_card_ids()
+    if contested_artist_card_ids is None:
+        contested_artist_card_ids = get_contested_artist_card_ids()
 
     printing_card = (
-        Card.objects.filter(printing_tag_status=PrintingTagStatus.UNRESOLVED, pk__in=get_contested_card_ids())
+        Card.objects.filter(printing_tag_status=PrintingTagStatus.UNRESOLVED, pk__in=contested_card_ids)
         .exclude(pk__in=answered_card_ids)
         .order_by("-date_created")
         .first()
@@ -493,7 +499,7 @@ def _tier_2_contested(
         return _identify_printing_item(printing_card), "tier_2_contested_printing"
 
     artist_card = (
-        Card.objects.filter(artist_vote_status=ArtistVoteStatus.CONTESTED, pk__in=get_contested_artist_card_ids())
+        Card.objects.filter(artist_vote_status=ArtistVoteStatus.CONTESTED, pk__in=contested_artist_card_ids)
         .exclude(pk__in=answered_artist_card_ids)
         .exclude(pk__in=not_official_art_card_ids)
         .order_by("-date_created")
@@ -537,6 +543,7 @@ def _tier_4_fresh(
     anonymous_id: str,
     answered_card_ids: Optional[set[int]] = None,
     not_official_art_card_ids: Optional[set[int]] = None,
+    contested_card_ids: Optional[list[int]] = None,
 ) -> Optional[tuple[QuestionFeedItem, str]]:
     # named "tier 4" (not renumbered to 3) even though moderation's former tier 3 was removed
     # (see module docstring) - keeps this name stable against every docstring/test/comment
@@ -563,9 +570,11 @@ def _tier_4_fresh(
         answered_card_ids = _voter_answered_printing_card_ids(anonymous_id)
     if not_official_art_card_ids is None:
         not_official_art_card_ids = _not_official_art_card_ids()
+    if contested_card_ids is None:
+        contested_card_ids = get_contested_card_ids()
     printing_card = (
         Card.objects.filter(printing_tag_status=PrintingTagStatus.UNRESOLVED)
-        .exclude(pk__in=get_contested_card_ids())
+        .exclude(pk__in=contested_card_ids)
         .exclude(pk__in=answered_card_ids)
         .annotate(vote_count=Count("printing_tags", distinct=True))
         .annotate(origin_reason=_latest_stage_d_origin_reason_subquery())
@@ -679,18 +688,33 @@ def get_next_question_feed_item(anonymous_id: str) -> Optional[QuestionFeedItem]
     if tier_1_item is not None:
         return _log_served(anonymous_id, tier_1_item, QuestionFeedServedPool.REMAINDER, "tier_1_confirm_suggestion")
 
+    # `contested_card_ids`/`contested_artist_card_ids` are resolved ONCE here, only once we've
+    # actually fallen through to the tiers that consult them (tier 1 and the likely-resolve pool
+    # above never touch either), and reused by both tier 2 and tier 4 below - each is otherwise
+    # identical on repeat calls within this same request (no vote can be cast mid-request), so
+    # recomputing it once per tier just paid the same cost twice for one answer.
+    contested_card_ids = get_contested_card_ids()
+    contested_artist_card_ids = get_contested_artist_card_ids()
+
     tier_2_result = _tier_2_contested(
         anonymous_id,
         answered_card_ids,
         answered_artist_card_ids=answered_artist_card_ids,
         answered_tag_card_ids_by_tag=answered_tag_card_ids_by_tag,
         not_official_art_card_ids=not_official_art_card_ids,
+        contested_card_ids=contested_card_ids,
+        contested_artist_card_ids=contested_artist_card_ids,
     )
     if tier_2_result is not None:
         tier_2_item, tier_2_reason = tier_2_result
         return _log_served(anonymous_id, tier_2_item, QuestionFeedServedPool.REMAINDER, tier_2_reason)
 
-    tier_4_result = _tier_4_fresh(anonymous_id, answered_card_ids, not_official_art_card_ids=not_official_art_card_ids)
+    tier_4_result = _tier_4_fresh(
+        anonymous_id,
+        answered_card_ids,
+        not_official_art_card_ids=not_official_art_card_ids,
+        contested_card_ids=contested_card_ids,
+    )
     if tier_4_result is not None:
         tier_4_item, tier_4_reason = tier_4_result
         return _log_served(anonymous_id, tier_4_item, QuestionFeedServedPool.REMAINDER, tier_4_reason)

MPCAutofill/cardpicker/tests/test_question_feed.py

@@ -1,7 +1,12 @@
+from unittest.mock import patch
+
 from django.urls import reverse
 
 from cardpicker import views
-from cardpicker.artist_consensus import resolve_and_persist_artist
+from cardpicker.artist_consensus import (
+    get_contested_artist_card_ids,
+    resolve_and_persist_artist,
+)
 from cardpicker.local_calculate_verdicts import (
     JOIN_KEY_ANONYMOUS_ID,
     JOIN_KEY_UNKNOWN_SET_CODE_SKIP_REASON,
@@ -17,7 +22,10 @@
     VotePolarity,
     VoteSource,
 )
-from cardpicker.printing_consensus import resolve_and_persist_printing
+from cardpicker.printing_consensus import (
+    get_contested_card_ids,
+    resolve_and_persist_printing,
+)
 from cardpicker.question_feed import (
     _artist_item,
     _scryfall_illustration_url,
@@ -213,6 +221,43 @@ def test_own_vote_exclusion_is_scoped_to_the_specific_tag_not_the_whole_card(sel
         assert item.tagName == tag_b.name
 
 
+class TestContestedIdsMemoizedPerRequest:
+    """`get_contested_card_ids`/`get_contested_artist_card_ids` are expensive (issue #726:
+    330-400ms each on production data) and, before this fix, were recomputed once per tier that
+    consulted them instead of once per `get_next_question_feed_item` call."""
+
+    def test_get_contested_card_ids_computed_once_when_tier_2_and_tier_4_are_both_consulted(self, db):
+        # a plain unresolved card with no votes: tier 2 finds nothing contested and falls
+        # through to tier 4, which - before this fix - called get_contested_card_ids() a
+        # second time for the same answer within the same request
+        card = CardFactory(printing_tag_status=PrintingTagStatus.UNRESOLVED)
+
+        with (
+            patch("cardpicker.question_feed.get_contested_card_ids", wraps=get_contested_card_ids) as mock_contested,
+            patch(
+                "cardpicker.question_feed.get_contested_artist_card_ids", wraps=get_contested_artist_card_ids
+            ) as mock_contested_artist,
+        ):
+            item = get_next_question_feed_item("anon-1")
+
+        assert item is not None
+        assert item.card.identifier == card.identifier
+        assert mock_contested.call_count == 1
+        assert mock_contested_artist.call_count == 1
+
+    def test_get_contested_card_ids_not_called_when_tier_1_serves_the_item(self, db):
+        # tier 1 (confirm_suggestion) and the likely-resolve pool both resolve before tier 2 is
+        # ever reached, so neither contested-ids function should run at all
+        make_ai_suggested_card()
+
+        with patch("cardpicker.question_feed.get_contested_card_ids", wraps=get_contested_card_ids) as mock_contested:
+            item = get_next_question_feed_item("anon-1")
+
+        assert item is not None
+        assert item.type.value == "confirm_suggestion"
+        assert mock_contested.call_count == 0
+
+
 class TestPhaseCNotOfficialArtRouting:
     """
     2026-08-04 gate on the phase-C/md5 routing brief (item 2): a card carrying a positive,