fix(tooltips): handle unreferenced aura upgrade values

src/BazaarPlusPlus/Game/Tooltips/UpgradePreviewValueRegistry.cs

@@ -8,6 +8,12 @@ namespace BazaarPlusPlus.Game.Tooltips;
 
 internal static class UpgradePreviewValueRegistry
 {
+    [ThreadStatic]
+    private static int _tooltipRenderDepth;
+
+    [ThreadStatic]
+    private static ITooltipComponent? _fallbackComponent;
+
     private static readonly ConditionalWeakTable<
         CardTooltipData,
         UpgradePreviewValueProjection
@@ -25,11 +31,39 @@ out float value
     )
     {
         value = default;
+        component ??= TakeFallbackComponent();
         return tooltipData != null
             && Projections.TryGetValue(tooltipData, out var projection)
             && projection.TryResolve(component, out value);
     }
 
+    internal static void BeginTooltipRender() => _tooltipRenderDepth++;
+
+    internal static void EndTooltipRender()
+    {
+        if (_tooltipRenderDepth > 0)
+            _tooltipRenderDepth--;
+
+        if (_tooltipRenderDepth == 0)
+            _fallbackComponent = null;
+    }
+
+    internal static void CaptureFallbackComponent(ITooltipComponent component)
+    {
+        // Native RenderTooltip omits the component argument for styled tokens whose
+        // ReferencedAttribute is null. Resolve() runs immediately before that formatter,
+        // so retain the token only for the duration of this synchronous render scope.
+        if (_tooltipRenderDepth > 0)
+            _fallbackComponent = component;
+    }
+
+    private static ITooltipComponent? TakeFallbackComponent()
+    {
+        var component = _fallbackComponent;
+        _fallbackComponent = null;
+        return component;
+    }
+
     internal static bool TryResolveEffectiveCooldowns(
         CardTooltipData tooltipData,
         out float currentSeconds,

src/BazaarPlusPlus/Patches/Tooltips/UpgradePreviewValuePatch.cs

@@ -2,13 +2,40 @@
 using System.Reflection;
 using BazaarGameClient.Domain.Tooltips;
 using BazaarGameShared.Domain.Core.Types;
+using BazaarGameShared.Domain.Effect.AuraActions;
 using BazaarPlusPlus.Game.Tooltips;
 using HarmonyLib;
 using TheBazaar;
 using TheBazaar.Tooltips;
 
 namespace BazaarPlusPlus.Patches.Tooltips;
 
+[HarmonyPatch(typeof(CardTooltipData), "RenderTooltip", [typeof(TooltipBuilder)])]
+internal static class UpgradePreviewTooltipRenderScopePatch
+{
+    [HarmonyPrefix]
+    private static void Prefix() => UpgradePreviewValueRegistry.BeginTooltipRender();
+
+    [HarmonyFinalizer]
+    private static void Finalizer() => UpgradePreviewValueRegistry.EndTooltipRender();
+}
+
+[HarmonyPatch(typeof(TooltipComponentAura), nameof(TooltipComponentAura.Resolve))]
+internal static class UpgradePreviewAuraValueContextPatch
+{
+    [HarmonyPostfix]
+    private static void Postfix(TooltipComponentAura __instance)
+    {
+        if (
+            !__instance.ReferencedAttribute.HasValue
+            && __instance.Aura.Action
+                is TAuraActionCardModifyAttribute
+                    or TAuraActionPlayerModifyAttribute
+        )
+            UpgradePreviewValueRegistry.CaptureFallbackComponent(__instance);
+    }
+}
+
 [HarmonyPatch]
 internal static class UpgradePreviewValuePatch
 {

tests/UpgradePreviewTooltip.Tests/Program.cs

@@ -104,6 +104,101 @@ out var projection
 );
 AssertFloatEqual(3f, upgradedBurn, "Derived Burn should be recomputed as 20% of 15, not 2 + 5.");
 
+var guzhengAura = new TCardAura
+{
+    Id = "guzheng-damage-per-tempo",
+    Action = new TAuraActionCardModifyAttribute
+    {
+        AttributeType = ECardAttributeType.DamageAmount,
+        Operation = EAttributeModifierOperation.Add,
+        Target = new TTargetCardSelf(),
+        Value = new TReferenceValuePlayerAttribute
+        {
+            AttributeType = EPlayerAttributeType.Tempo,
+            Modifier = new TValueModifier
+            {
+                ModifyMode = EValueModifierMode.Multiply,
+                Value = new TReferenceValueCardAttribute
+                {
+                    AttributeType = ECardAttributeType.Custom_0,
+                    Target = new TTargetCardSelf(),
+                    Modifier = new TValueModifier
+                    {
+                        ModifyMode = EValueModifierMode.Multiply,
+                        Value = new TFixedValue { Value = 1f },
+                    },
+                },
+            },
+        },
+    },
+};
+var guzhengTemplate = new TCardItem
+{
+    Type = ECardType.Item,
+    StartingTier = ETier.Gold,
+    Auras = new Dictionary<string, TCardAura> { [guzhengAura.Id] = guzhengAura },
+    Tiers = new Dictionary<ETier, TCardTier>
+    {
+        [ETier.Gold] = new TCardTier
+        {
+            Attributes = new Dictionary<ECardAttributeType, int>
+            {
+                [ECardAttributeType.Custom_0] = 15,
+            },
+        },
+        [ETier.Diamond] = new TCardTier
+        {
+            Attributes = new Dictionary<ECardAttributeType, int>
+            {
+                [ECardAttributeType.Custom_0] = 30,
+            },
+        },
+    },
+};
+var guzhengCard = new ItemCard
+{
+    Template = guzhengTemplate,
+    Type = ECardType.Item,
+    Tier = ETier.Gold,
+    Attributes = new Dictionary<ECardAttributeType, int> { [ECardAttributeType.Custom_0] = 15 },
+};
+var guzhengContext = new TooltipContext(
+    guzhengCard,
+    guzhengTemplate,
+    new ValueContext(null!, guzhengCard)
+);
+var guzhengToken = TooltipComponentAura.Create(
+    guzhengContext,
+    guzhengAura.Id,
+    ETooltipAccessorType.Mod,
+    0
+);
+
+AssertNotNull(guzhengToken, "Guzheng aura token should be created.");
+AssertTrue(
+    !guzhengToken!.ReferencedAttribute.HasValue,
+    "Guzheng's player-attribute aura intentionally has no native referenced card attribute."
+);
+AssertFloatEqual(15f, guzhengToken.Resolve()!.Value, "Current Guzheng multiplier should be 15.");
+AssertTrue(
+    UpgradePreviewValueProjection.TryCreate(
+        guzhengCard,
+        guzhengTemplate,
+        guzhengContext.ValueContext,
+        out var guzhengProjection
+    ),
+    "Guzheng upgrade projection should be created."
+);
+AssertTrue(
+    guzhengProjection.TryResolve(guzhengToken, out var upgradedGuzhengMultiplier),
+    "Projected Guzheng aura token should resolve."
+);
+AssertFloatEqual(
+    30f,
+    upgradedGuzhengMultiplier,
+    "Guzheng Damage and Shield per Tempo should upgrade from 15 to 30."
+);
+
 card.Attributes[ECardAttributeType.Custom_1] = 12;
 AssertTrue(
     UpgradePreviewValueProjection.TryCreate(