add csfloat api usage

BlueLaminate/BlueLaminate.EFCore/Entities/SkinInstance.cs

@@ -1,20 +1,50 @@
 namespace BlueLaminate.EFCore.Entities;
 
+/// <summary>
+/// One physical CS2 item, identified by its fingerprint
+/// (Skin + FloatValue + PaintSeed + StatTrak + Souvenir) rather than its Steam
+/// asset id, which changes on every trade. Decoupled from Steam inventories on
+/// purpose: an instance exists from market observation alone, and the optional
+/// <see cref="InventoryItem"/> bridge ties it to a <c>SteamUser</c> only once we
+/// crawl inventories.
+///
+/// Duping note: a duplicated item is a byte-for-byte copy with an identical
+/// fingerprint, so a fingerprint is NOT guaranteed unique to one physical item.
+/// We treat the fingerprint as the item, and flag <see cref="SuspectedDupe"/>
+/// when the same fingerprint is seen live under two or more different asset ids
+/// at once (see the sweep's dupe detection).
+/// </summary>
 public class SkinInstance
 {
     public int Id { get; set; }
     public int SkinId { get; set; }
     public Skin Skin { get; set; } = null!;
-    public int ConditionId { get; set; }
-    public SkinCondition Condition { get; set; } = null!;
 
-    // FloatValue + PaintSeed form a stable fingerprint across trades; the Steam
-    // asset_id changes on every trade but these do not.
+    // Nullable: market observation gives a float but not a derived wear bucket.
+    // Condition can be backfilled later from the float without blocking ingest.
+    public int? ConditionId { get; set; }
+    public SkinCondition? Condition { get; set; }
+
+    // The fingerprint. FloatValue is stored at full precision (see config) so
+    // that exact-match dupe detection isn't fooled by rounding.
     public decimal FloatValue { get; set; }
     public string PaintSeed { get; set; } = null!;
     public bool StatTrak { get; set; }
     public bool Souvenir { get; set; }
     public DateTimeOffset FirstSeenAt { get; set; }
+    public DateTimeOffset LastSeenAt { get; set; }
+
+    /// <summary>
+    /// True once this fingerprint was observed live under 2+ distinct asset ids
+    /// simultaneously — the signature of duplication.
+    /// </summary>
+    public bool SuspectedDupe { get; set; }
+
+    /// <summary>When the dupe condition was first detected. Null until then.</summary>
+    public DateTimeOffset? DupeFirstSeenAt { get; set; }
+
+    /// <summary>Every market listing observed for this physical item over time.</summary>
+    public ICollection<Listing> Listings { get; set; } = new List<Listing>();
 
     public ICollection<InventoryItem> InventoryItems { get; set; } = new List<InventoryItem>();
 }