feat(inventory): add ViewerAcquireHistoryEntry entity + DbSet

Adds the ViewerAcquireHistoryEntry model (8 fields: Id, ViewerId,
RewardType, RewardDetailId, RewardCount, AcquireType, Message,
AcquireTime), registers DbSet<ViewerAcquireHistoryEntry> on
SVSimDbContext, configures model (PK, FK cascade to Viewer, MaxLength
64 on Message, composite index on ViewerId/AcquireTime/Id), and adds a
DbSet round-trip integration test.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.Database/Models/ViewerAcquireHistoryEntry.cs

@@ -0,0 +1,30 @@
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// One row per grant emitted by <c>InventoryTransaction.CommitAsync</c>. Rendered as the
+/// <c>histories[]</c> array on <c>POST /item_acquire_history/info</c>. Capped at 300 rows
+/// per viewer; oldest pruned on commit.
+/// </summary>
+public sealed class ViewerAcquireHistoryEntry
+{
+    public long Id { get; set; }
+    public long ViewerId { get; set; }
+
+    /// <summary>UserGoodsType cast to int; matches the wire <c>reward_type</c>.</summary>
+    public int RewardType { get; set; }
+
+    /// <summary>Detail id for the goods; 0 for wallet currencies.</summary>
+    public long RewardDetailId { get; set; }
+
+    /// <summary>Delta granted in this row — NOT a post-state total.</summary>
+    public int RewardCount { get; set; }
+
+    /// <summary>GrantSource cast to int; matches the wire <c>acquire_type</c>.</summary>
+    public int AcquireType { get; set; }
+
+    /// <summary>Pre-localized text the client renders verbatim. Capped at 64 chars.</summary>
+    public string Message { get; set; } = string.Empty;
+
+    /// <summary>Server UTC at commit time. Stamped once per <c>CommitAsync</c>, identical across all rows in that commit.</summary>
+    public DateTime AcquireTime { get; set; }
+}

SVSim.Database/SVSimDbContext.cs

@@ -103,6 +103,7 @@ public class SVSimDbContext : DbContext
 
     public DbSet<ViewerPresent> ViewerPresents => Set<ViewerPresent>();
     public DbSet<TutorialPresentEntry> TutorialPresentEntries => Set<TutorialPresentEntry>();
+    public DbSet<ViewerAcquireHistoryEntry> ViewerAcquireHistory => Set<ViewerAcquireHistoryEntry>();
 
     public DbSet<ArenaTwoPickReward> ArenaTwoPickRewards { get; set; } = null!;
     public DbSet<ViewerArenaTwoPickRun> ViewerArenaTwoPickRuns { get; set; } = null!;
@@ -398,6 +399,19 @@ public class SVSimDbContext : DbContext
             b.Property(p => p.PresentId).HasMaxLength(64);
         });
 
+        modelBuilder.Entity<ViewerAcquireHistoryEntry>(b =>
+        {
+            b.HasKey(e => e.Id);
+            b.Property(e => e.Id).ValueGeneratedOnAdd();
+            b.Property(e => e.Message).HasMaxLength(64).IsRequired();
+            b.HasOne<Viewer>()
+                .WithMany()
+                .HasForeignKey(e => e.ViewerId)
+                .OnDelete(DeleteBehavior.Cascade);
+            b.HasIndex(e => new { e.ViewerId, e.AcquireTime, e.Id })
+                .HasDatabaseName("IX_ViewerAcquireHistory_ViewerId_AcquireTime_Id");
+        });
+
         base.OnModelCreating(modelBuilder);
     }
 

SVSim.UnitTests/Services/Inventory/InventoryHistoryTests.cs

@@ -1,3 +1,5 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
 using SVSim.Database.Services.Inventory;
 
 namespace SVSim.UnitTests.Services.Inventory;
@@ -37,4 +39,31 @@ public class InventoryHistoryTests
         var cfg = new InventoryLoadConfig { Source = GrantSource.PackOpen };
         Assert.That(cfg.Source, Is.EqualTo(GrantSource.PackOpen));
     }
+
+    [Test]
+    public async Task ViewerAcquireHistory_DbSet_round_trips_a_row()
+    {
+        using var factory = new SVSim.UnitTests.Infrastructure.SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        using var scope = factory.Services.CreateScope();
+        var ctx = scope.ServiceProvider.GetRequiredService<SVSim.Database.SVSimDbContext>();
+
+        ctx.ViewerAcquireHistory.Add(new SVSim.Database.Models.ViewerAcquireHistoryEntry
+        {
+            ViewerId = viewerId,
+            RewardType = (int)SVSim.Database.Enums.UserGoodsType.Rupy,
+            RewardDetailId = 0,
+            RewardCount = 50,
+            AcquireType = (int)GrantSource.DailyBonus,
+            Message = "Daily Bonus",
+            AcquireTime = new DateTime(2026, 6, 9, 12, 0, 0, DateTimeKind.Utc),
+        });
+        await ctx.SaveChangesAsync();
+
+        var roundtrip = await ctx.ViewerAcquireHistory.AsNoTracking()
+            .Where(h => h.ViewerId == viewerId).ToListAsync();
+        Assert.That(roundtrip, Has.Count.EqualTo(1));
+        Assert.That(roundtrip[0].RewardCount, Is.EqualTo(50));
+        Assert.That(roundtrip[0].AcquireType, Is.EqualTo((int)GrantSource.DailyBonus));
+    }
 }