feat(inventory): prune acquire history above 300-row cap

Adds PruneAcquireHistoryAsync to InventoryTransaction.CommitAsync; runs
inside the open DB transaction after history rows are flushed, keeping at
most 300 rows per viewer (oldest discarded). Adds a covering test that
verifies the cap and per-viewer isolation.

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

SVSim.Database/Services/Inventory/InventoryTransaction.cs

@@ -9,6 +9,8 @@ namespace SVSim.Database.Services.Inventory;
 
 internal sealed class InventoryTransaction : IInventoryTransaction
 {
+    private const int AcquireHistoryRetention = 300;
+
     private readonly SVSimDbContext _db;
     private readonly IDbContextTransaction _dbTx;
     private readonly ILogger _log;
@@ -282,6 +284,8 @@ internal sealed class InventoryTransaction : IInventoryTransaction
         WriteAcquireHistory();
         await _db.SaveChangesAsync(ct);
 
+        await PruneAcquireHistoryAsync(ct);
+
         await _dbTx.CommitAsync(ct);
         _committed = true;
 
@@ -290,6 +294,22 @@ internal sealed class InventoryTransaction : IInventoryTransaction
         return new InventoryCommitResult(rewardList, deltas);
     }
 
+    private async Task PruneAcquireHistoryAsync(CancellationToken ct)
+    {
+        var overflowIds = await _db.ViewerAcquireHistory
+            .Where(h => h.ViewerId == Viewer.Id)
+            .OrderByDescending(h => h.AcquireTime).ThenByDescending(h => h.Id)
+            .Skip(AcquireHistoryRetention)
+            .Select(h => h.Id)
+            .ToListAsync(ct);
+
+        if (overflowIds.Count == 0) return;
+
+        await _db.ViewerAcquireHistory
+            .Where(h => overflowIds.Contains(h.Id))
+            .ExecuteDeleteAsync(ct);
+    }
+
     private void WriteAcquireHistory()
     {
         var now = DateTime.UtcNow;

SVSim.UnitTests/Services/Inventory/InventoryHistoryTests.cs

@@ -241,4 +241,38 @@ public class InventoryHistoryTests
             .Where(h => h.ViewerId == viewerId).FirstAsync();
         Assert.That(row.RewardDetailId, Is.EqualTo(0));
     }
+
+    [Test]
+    public async Task Commit_prunes_history_above_retention_cap_per_viewer()
+    {
+        using var factory = new SVSim.UnitTests.Infrastructure.SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync(steamId: 76_561_198_000_000_001UL);
+        long otherViewerId = await factory.SeedViewerAsync(steamId: 76_561_198_000_000_002UL);
+        using var scope = factory.Services.CreateScope();
+        var inv = scope.ServiceProvider.GetRequiredService<SVSim.Database.Services.Inventory.IInventoryService>();
+
+        // Pre-seed 305 rows for the primary viewer via 305 single-grant commits.
+        for (int i = 0; i < 305; i++)
+        {
+            await using var tx = await inv.BeginAsync(viewerId, configure: c => c.Source = GrantSource.DailyBonus);
+            await tx.GrantAsync(SVSim.Database.Enums.UserGoodsType.Rupy, 0, 1);
+            await tx.CommitAsync();
+        }
+
+        // Seed 50 rows for an unrelated viewer to verify pruning is per-viewer.
+        for (int i = 0; i < 50; i++)
+        {
+            await using var tx = await inv.BeginAsync(otherViewerId, configure: c => c.Source = GrantSource.DailyBonus);
+            await tx.GrantAsync(SVSim.Database.Enums.UserGoodsType.Rupy, 0, 1);
+            await tx.CommitAsync();
+        }
+
+        using var verifyScope = factory.Services.CreateScope();
+        var ctx = verifyScope.ServiceProvider.GetRequiredService<SVSim.Database.SVSimDbContext>();
+        var primaryCount = await ctx.ViewerAcquireHistory.CountAsync(h => h.ViewerId == viewerId);
+        var otherCount = await ctx.ViewerAcquireHistory.CountAsync(h => h.ViewerId == otherViewerId);
+
+        Assert.That(primaryCount, Is.EqualTo(300), "primary viewer pruned to cap");
+        Assert.That(otherCount, Is.EqualTo(50), "other viewer untouched by primary's prune");
+    }
 }