Pack logic cleanup

SVSim.EmulatedEntrypoint/Services/ICardPoolProvider.cs

@@ -6,4 +6,12 @@ namespace SVSim.EmulatedEntrypoint.Services;
 public interface ICardPoolProvider
 {
     IReadOnlyList<ShadowverseCardEntry> GetPool(PackConfigEntry pack);
+
+    /// <summary>
+    /// Returns the foil twin of <paramref name="baseCardId"/> if it exists in master data
+    /// (foil card_id = base card_id + 1 by the cards.json convention), else null. One DB
+    /// hit per call; expected ~0.64 calls per 8-card pack at the default 8% rate.
+    /// TODO(caching): folds into the broader caching wave once one exists.
+    /// </summary>
+    ShadowverseCardEntry? TryGetFoilTwin(long baseCardId);
 }