diff --git a/SVSim.EmulatedEntrypoint/Controllers/BuildDeckController.cs b/SVSim.EmulatedEntrypoint/Controllers/BuildDeckController.cs
index 01e12df..414befd 100644
--- a/SVSim.EmulatedEntrypoint/Controllers/BuildDeckController.cs
+++ b/SVSim.EmulatedEntrypoint/Controllers/BuildDeckController.cs
@@ -1,10 +1,9 @@
 using Microsoft.AspNetCore.Mvc;
-using Microsoft.EntityFrameworkCore;
-using SVSim.Database;
 using SVSim.Database.Enums;
 using SVSim.Database.Models;
 using SVSim.Database.Repositories.BuildDeck;
 using SVSim.Database.Services;
+using SVSim.Database.Services.Inventory;
 using SVSim.EmulatedEntrypoint.Models.Dtos;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Requests.BuildDeck;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Responses.BuildDeck;
@@ -20,39 +19,16 @@ namespace SVSim.EmulatedEntrypoint.Controllers;
 public class BuildDeckController : SVSimController
 {
     private readonly IBuildDeckRepository _repo;
-    private readonly SVSimDbContext _db;
-    private readonly RewardGrantService _rewards;
-    private readonly ICurrencySpendService _spend;
+    private readonly IInventoryService _inv;
 
     public BuildDeckController(
         IBuildDeckRepository repo,
-        SVSimDbContext db,
-        RewardGrantService rewards,
-        ICurrencySpendService spend)
+        IInventoryService inv)
     {
         _repo = repo;
-        _db = db;
-        _rewards = rewards;
-        _spend = spend;
+        _inv = inv;
     }
 
-    /// <summary>
-    /// Loads the viewer with the full cosmetic / inventory graph + BuildDeckPurchases. This is
-    /// the single load /build_deck/buy makes; every subsequent mutation operates on the returned
-    /// instance and the controller saves once at the end.
-    /// </summary>
-    private Task<Viewer> LoadViewerGraphAsync(long viewerId) => _db.Viewers
-        .Include(v => v.Cards).ThenInclude(c => c.Card)
-        .Include(v => v.LeaderSkins)
-        .Include(v => v.Sleeves)
-        .Include(v => v.Emblems)
-        .Include(v => v.Degrees)
-        .Include(v => v.MyPageBackgrounds)
-        .Include(v => v.Items).ThenInclude(i => i.Item)
-        .Include(v => v.BuildDeckPurchases)
-        .AsSplitQuery()
-        .FirstAsync(v => v.Id == viewerId);
-
     // The wire shape for /build_deck/info has `data` as a bare collection of series, not a
     // DTO with a `series_list` field. The client (BuildDeckPurchaseInfoTask.Parse) iterates
     // `data` directly via numeric indexer:
@@ -194,60 +170,45 @@ public class BuildDeckController : SVSimController
                 break;
         }
 
-        // Single viewer load with the full graph — every subsequent mutation (currency debit,
-        // purchase counter, card grants, cosmetic grants) operates on this one in-memory instance
-        // so we can save once at the end.
-        var viewer = await LoadViewerGraphAsync(viewerId);
-        var rewardList = new List<RewardListEntry>();
+        // Open the inventory transaction — loads canonical graph + BuildDeckPurchases.
+        await using var tx = await _inv.BeginAsync(viewerId, HttpContext.RequestAborted,
+            cfg => cfg.WithInclude(v => v.BuildDeckPurchases));
+        var viewer = tx.Viewer;
 
-        // Debit + post-state currency entry
+        // Debit currency
         if (request.SalesType == 1)
         {
-            var r = await _spend.TrySpendAsync(viewer, SpendCurrency.Crystal, priceCrystal!.Value);
+            var r = await tx.TrySpendAsync(SpendCurrency.Crystal, priceCrystal!.Value);
             if (!r.Success) return BadRequest(new { error = "insufficient_crystals" });
-            rewardList.Add(new RewardListEntry { RewardType = 2, RewardId = 0, RewardNum = (int)r.PostStateTotal });
         }
         else if (request.SalesType == 2)
         {
-            var r = await _spend.TrySpendAsync(viewer, SpendCurrency.Rupee, priceRupy!.Value);
+            var r = await tx.TrySpendAsync(SpendCurrency.Rupee, priceRupy!.Value);
             if (!r.Success) return BadRequest(new { error = "insufficient_rupees" });
-            rewardList.Add(new RewardListEntry { RewardType = 9, RewardId = 0, RewardNum = (int)r.PostStateTotal });
         }
-        // sales_type == 0 (free): no debit, no currency entry
+        // sales_type == 0 (free): no debit
 
         // Compute series purchase total BEFORE this buy
         int prevSeriesCount = product.Series!.Products
             .Sum(p => purchases.TryGetValue(p.Id, out var v) ? v.PurchaseCount : 0);
         int newSeriesCount = prevSeriesCount + 1;
 
-        // Increment purchase counter directly on the tracked viewer (we already loaded
-        // BuildDeckPurchases via LoadViewerGraphAsync). The repo's IncrementPurchaseCount would
-        // re-attach to the same instance and trigger an extra save — inlining keeps the
-        // controller's single-save model intact.
+        // Increment purchase counter on tx.Viewer (tx loaded BuildDeckPurchases via WithInclude).
         var purchaseRow = viewer.BuildDeckPurchases.FirstOrDefault(p => p.ProductId == product.Id);
         if (purchaseRow is null)
             viewer.BuildDeckPurchases.Add(new ViewerBuildDeckProductPurchase { ProductId = product.Id, PurchaseCount = 1 });
         else
             purchaseRow.PurchaseCount += 1;
 
-        // Grant the 40 deck cards. Bucket by CardId so duplicate (CardId, IsSpot) rows don't
-        // emit redundant reward_list entries — ApplyAsync(Card, ...) runs the cosmetic cascade
-        // and returns a post-state-total entry per call.
-        var deckGrants = product.Cards
-            .GroupBy(c => c.CardId)
-            .Select(g => (UserGoodsType.Card, g.Key, g.Sum(c => c.Number)));
-        await ApplyRewardsAsync(viewer, deckGrants, rewardList);
+        // Grant deck cards (grouped by CardId)
+        foreach (var grp in product.Cards.GroupBy(c => c.CardId))
+            await tx.GrantAsync(UserGoodsType.Card, grp.Key, grp.Sum(c => c.Number));
 
-        // Per-buy rewards from the product catalog: sleeve, emblem, skin, sometimes extra cards
-        // (Set 4 grants 3 copies of the featured card as a type=5 reward).
-        await ApplyRewardsAsync(viewer, product.Rewards
-            .OrderBy(r => r.RewardIndex)
-            .Select(r => ((UserGoodsType)r.RewardType, r.RewardDetailId, r.RewardNumber)),
-            rewardList);
+        // Per-buy rewards
+        foreach (var r in product.Rewards.OrderBy(r => r.RewardIndex))
+            await tx.GrantAsync((UserGoodsType)r.RewardType, r.RewardDetailId, r.RewardNumber);
 
-        // Series-reward tier crossings: tiers where prevSeriesCount < TierIndex <= newSeriesCount.
-        // Captured tiers include type 4 (Item), 5 (Card), 6 (Sleeve), 7 (Emblem) — granting them
-        // all uniformly avoids the earlier card-only path that dropped non-card tier rewards.
+        // Series-reward tier crossings
         var crossedTiers = product.Series.SeriesRewards
             .Where(r => r.TierIndex > prevSeriesCount && r.TierIndex <= newSeriesCount)
             .GroupBy(r => r.TierIndex)
@@ -257,13 +218,9 @@ public class BuildDeckController : SVSimController
         var seriesRewards = new List<BuildDeckProductRewardDto>();
         foreach (var tier in crossedTiers)
         {
-            await ApplyRewardsAsync(viewer, tier
-                .OrderBy(r => r.ItemIndex)
-                .Select(r => ((UserGoodsType)r.RewardType, r.RewardDetailId, r.RewardNumber)),
-                rewardList);
-
             foreach (var item in tier.OrderBy(r => r.ItemIndex))
             {
+                await tx.GrantAsync((UserGoodsType)item.RewardType, item.RewardDetailId, item.RewardNumber);
                 seriesRewards.Add(new BuildDeckProductRewardDto
                 {
                     RewardType = item.RewardType,
@@ -274,39 +231,17 @@ public class BuildDeckController : SVSimController
             }
         }
 
-        await _db.SaveChangesAsync();
+        var result = await tx.CommitAsync(HttpContext.RequestAborted);
 
         return new BuildDeckBuyResponse
         {
-            RewardList = rewardList,
+            RewardList = result.RewardList
+                .Select(g => new RewardListEntry { RewardType = g.RewardType, RewardId = g.RewardId, RewardNum = g.RewardNum })
+                .ToList(),
             SeriesRewards = seriesRewards,
         };
     }
 
-    /// <summary>
-    /// Dispatches each (type, id, num) tuple through <see cref="RewardGrantService.ApplyAsync"/>
-    /// and appends the resulting wire entries to <paramref name="rewardList"/>. Caller saves.
-    /// </summary>
-    private async Task ApplyRewardsAsync(
-        Viewer viewer,
-        IEnumerable<(UserGoodsType Type, long DetailId, int Number)> rewards,
-        List<RewardListEntry> rewardList)
-    {
-        foreach (var (type, detailId, number) in rewards)
-        {
-            var granted = await _rewards.ApplyAsync(viewer, type, detailId, number);
-            foreach (var g in granted)
-            {
-                rewardList.Add(new RewardListEntry
-                {
-                    RewardType = g.RewardType,
-                    RewardId = g.RewardId,
-                    RewardNum = g.RewardNum,
-                });
-            }
-        }
-    }
-
     [HttpPost("get_purchase_count")]
     public async Task<ActionResult<BuildDeckGetPurchaseCountResponse>> GetPurchaseCount(
         BuildDeckGetPurchaseCountRequest request)