Distribution/Data/AppDBContext.cs

@@ -41,6 +41,12 @@ public class AppDBContext(DbContextOptions<AppDBContext> options) : DbContext(op
     public DbSet<SchemeBundleComponent> SchemeBundleComponents { get; set; }
     public DbSet<LoadingSheet> LoadingSheets { get; set; }
     public DbSet<LoadingSheetItem> LoadingSheetItems { get; set; }
+    public DbSet<PurchaseOrder> PurchaseOrders { get; set; }
+    public DbSet<PurchaseOrderItem> PurchaseOrderItems { get; set; }
+    public DbSet<GoodsReceipt> GoodsReceipts { get; set; }
+    public DbSet<GoodsReceiptItem> GoodsReceiptItems { get; set; }
+    public DbSet<PurchaseReturn> PurchaseReturns { get; set; }
+    public DbSet<PurchaseReturnItem> PurchaseReturnItems { get; set; }
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
@@ -160,6 +166,78 @@ public class AppDBContext(DbContextOptions<AppDBContext> options) : DbContext(op
             .HasForeignKey(i => i.FK_ItemId)
             .OnDelete(DeleteBehavior.Restrict);
 
+        modelBuilder.Entity<PurchaseOrder>()
+            .HasOne(po => po.Supplier)
+            .WithMany()
+            .HasForeignKey(po => po.FK_SupplierId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        modelBuilder.Entity<PurchaseOrderItem>()
+            .HasOne(i => i.PurchaseOrder)
+            .WithMany(po => po.Items)
+            .HasForeignKey(i => i.FK_PurchaseOrderId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        modelBuilder.Entity<PurchaseOrderItem>()
+            .HasOne(i => i.Item)
+            .WithMany()
+            .HasForeignKey(i => i.FK_ItemId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        modelBuilder.Entity<GoodsReceipt>()
+            .HasOne(gr => gr.PurchaseOrder)
+            .WithMany()
+            .HasForeignKey(gr => gr.FK_PurchaseOrderId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        modelBuilder.Entity<GoodsReceipt>()
+            .HasOne(gr => gr.Warehouse)
+            .WithMany()
+            .HasForeignKey(gr => gr.FK_WarehouseId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        modelBuilder.Entity<GoodsReceiptItem>()
+            .HasOne(i => i.GoodsReceipt)
+            .WithMany(gr => gr.Items)
+            .HasForeignKey(i => i.FK_GoodsReceiptId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        modelBuilder.Entity<GoodsReceiptItem>()
+            .HasOne(i => i.PurchaseOrderItem)
+            .WithMany()
+            .HasForeignKey(i => i.FK_PurchaseOrderItemId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        modelBuilder.Entity<PurchaseReturn>()
+            .HasOne(pr => pr.PurchaseOrder)
+            .WithMany()
+            .HasForeignKey(pr => pr.FK_PurchaseOrderId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        modelBuilder.Entity<PurchaseReturnItem>()
+            .HasOne(i => i.PurchaseReturn)
+            .WithMany(pr => pr.Items)
+            .HasForeignKey(i => i.FK_PurchaseReturnId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        modelBuilder.Entity<PurchaseReturnItem>()
+            .HasOne(i => i.Item)
+            .WithMany()
+            .HasForeignKey(i => i.FK_ItemId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        modelBuilder.Entity<PurchaseOrderItem>()
+            .HasIndex(i => i.FK_PurchaseOrderId);
+
+        modelBuilder.Entity<GoodsReceiptItem>()
+            .HasIndex(i => i.FK_GoodsReceiptId);
+
+        modelBuilder.Entity<GoodsReceiptItem>()
+            .HasIndex(i => i.FK_PurchaseOrderItemId);
+
+        modelBuilder.Entity<PurchaseReturnItem>()
+            .HasIndex(i => i.FK_PurchaseReturnId);
+
         Seed.RoleAndPermissionSeed.Apply(modelBuilder);
     }
 }

Distribution/Features/Grn/GrnController.cs

@@ -0,0 +1,33 @@
+using Distribution.Infra.Authorization;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Distribution.Features.Grn;
+
+[ApiController]
+[Authorize]
+public class GrnController(GrnService service, ICurrentUserService currentUser) : ControllerBase
+{
+    [HttpGet("api/goods-receipts/{id:guid}")]
+    public async Task<IActionResult> GetById(Guid id)
+    {
+        var result = await service.GetByIdAsync(id);
+        return result is null ? NotFound() : Ok(result);
+    }
+
+    [HttpGet("api/purchase-orders/{id:guid}/goods-receipts")]
+    public async Task<IActionResult> GetByPurchaseOrder(Guid id) =>
+        Ok(await service.GetByPurchaseOrderIdAsync(id));
+
+    [HttpPost("api/purchase-orders/{id:guid}/goods-receipts")]
+    public async Task<IActionResult> Create(Guid id, CreateGrnRequest request, CancellationToken ct)
+    {
+        var userId = currentUser.UserId ?? throw new UnauthorizedAccessException();
+        try
+        {
+            var result = await service.CreateAsync(id, request, userId, ct);
+            return CreatedAtAction(nameof(GetById), new { id = result.Id }, result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+}

Distribution/Features/Grn/GrnDTOs.cs

@@ -0,0 +1,24 @@
+namespace Distribution.Features.Grn;
+
+public record GrnItemRequest(Guid PurchaseOrderItemId, int AcceptedQuantity, int RejectedQuantity);
+
+public record CreateGrnRequest(Guid WarehouseId, List<GrnItemRequest> Items);
+
+public record GrnItemResponse(
+    Guid Id,
+    Guid PurchaseOrderItemId,
+    Guid ItemId,
+    string Sku,
+    string ItemName,
+    int AcceptedQuantity,
+    int RejectedQuantity);
+
+public record GrnResponse(
+    Guid Id,
+    Guid PurchaseOrderId,
+    Guid ReceivedByUserId,
+    Guid WarehouseId,
+    string WarehouseName,
+    DateTime ReceivedAt,
+    DateTime CreatedAt,
+    List<GrnItemResponse> Items);

Distribution/Features/Grn/GrnRepository.cs

@@ -0,0 +1,35 @@
+using Distribution.Data;
+using Microsoft.EntityFrameworkCore;
+
+namespace Distribution.Features.Grn;
+
+public class GrnRepository(AppDBContext context) : IGrnRepository
+{
+    public async Task<Models.GoodsReceipt?> GetByIdAsync(Guid id) =>
+        await context.GoodsReceipts
+            .Include(gr => gr.Warehouse)
+            .Include(gr => gr.Items).ThenInclude(i => i.PurchaseOrderItem).ThenInclude(poi => poi.Item)
+            .FirstOrDefaultAsync(gr => gr.Id == id);
+
+    public async Task<List<Models.GoodsReceipt>> GetByPurchaseOrderIdAsync(Guid purchaseOrderId) =>
+        await context.GoodsReceipts
+            .Include(gr => gr.Warehouse)
+            .Include(gr => gr.Items).ThenInclude(i => i.PurchaseOrderItem).ThenInclude(poi => poi.Item)
+            .Where(gr => gr.FK_PurchaseOrderId == purchaseOrderId && gr.IsActive)
+            .OrderByDescending(gr => gr.ReceivedAt)
+            .ToListAsync();
+
+    public async Task AddAsync(Models.GoodsReceipt entity) =>
+        await context.GoodsReceipts.AddAsync(entity);
+
+    public async Task<bool> HasAnyForPurchaseOrderAsync(Guid purchaseOrderId) =>
+        await context.GoodsReceipts.AnyAsync(gr => gr.FK_PurchaseOrderId == purchaseOrderId && gr.IsActive);
+
+    public async Task<Dictionary<Guid, int>> GetAcceptedTotalsByItemAsync(Guid purchaseOrderId) =>
+        await context.GoodsReceiptItems
+            .Include(i => i.PurchaseOrderItem)
+            .Where(i => i.PurchaseOrderItem.FK_PurchaseOrderId == purchaseOrderId && i.IsActive)
+            .GroupBy(i => i.PurchaseOrderItem.FK_ItemId)
+            .Select(g => new { ItemId = g.Key, Total = g.Sum(i => i.AcceptedQuantity) })
+            .ToDictionaryAsync(x => x.ItemId, x => x.Total);
+}

Distribution/Features/Grn/GrnService.cs

@@ -0,0 +1,137 @@
+using Distribution.Features.Po;
+using Distribution.Features.Stock;
+using Distribution.Infra.UoW;
+using Distribution.Models;
+
+namespace Distribution.Features.Grn;
+
+public class GrnService(
+    IGrnRepository repo,
+    IPoRepository poRepo,
+    IStockRepository stockRepo,
+    IUnitOfWork uow)
+{
+    private static GrnItemResponse MapItem(Models.GoodsReceiptItem i) =>
+        new(i.Id, i.FK_PurchaseOrderItemId, i.PurchaseOrderItem.FK_ItemId, i.PurchaseOrderItem.Item.Sku,
+            i.PurchaseOrderItem.Item.Name, i.AcceptedQuantity, i.RejectedQuantity);
+
+    private static GrnResponse Map(Models.GoodsReceipt gr) =>
+        new(gr.Id, gr.FK_PurchaseOrderId, gr.FK_ReceivedByUserId, gr.FK_WarehouseId, gr.Warehouse?.Name ?? string.Empty,
+            gr.ReceivedAt, gr.CreatedAt, gr.Items.Where(i => i.IsActive).Select(MapItem).ToList());
+
+    public async Task<GrnResponse?> GetByIdAsync(Guid id)
+    {
+        var gr = await repo.GetByIdAsync(id);
+        if (gr is null || !gr.IsActive) return null;
+        return Map(gr);
+    }
+
+    public async Task<List<GrnResponse>> GetByPurchaseOrderIdAsync(Guid purchaseOrderId) =>
+        (await repo.GetByPurchaseOrderIdAsync(purchaseOrderId)).Select(Map).ToList();
+
+    /// <summary>
+    /// Validates the Po status, increments PurchaseOrderItem.ReceivedQuantity, writes StockBalance/
+    /// StockMovement for AcceptedQuantity only (RejectedQuantity never touches stock), and
+    /// transitions the Po to PartiallyReceived/Received. All in one unit of work.
+    /// </summary>
+    public async Task<GrnResponse> CreateAsync(Guid purchaseOrderId, CreateGrnRequest request, Guid receivedByUserId, CancellationToken ct = default)
+    {
+        var po = await poRepo.GetByIdAsync(purchaseOrderId)
+            ?? throw new InvalidOperationException("Purchase order not found.");
+
+        if (!po.IsActive)
+            throw new InvalidOperationException("Purchase order not found.");
+
+        if (po.Status is not (PurchaseOrderStatus.Issued or PurchaseOrderStatus.PartiallyReceived))
+            throw new InvalidOperationException(
+                $"Cannot receive goods against a purchase order in {po.Status} status.");
+
+        if (request.Items is null || request.Items.Count == 0)
+            throw new InvalidOperationException("A goods receipt must have at least one line item.");
+
+        var goodsReceipt = new Models.GoodsReceipt
+        {
+            FK_PurchaseOrderId = po.Id,
+            FK_ReceivedByUserId = receivedByUserId,
+            FK_WarehouseId = request.WarehouseId,
+            ReceivedAt = DateTime.Now
+        };
+
+        foreach (var line in request.Items)
+        {
+            var poItem = po.Items.FirstOrDefault(i => i.Id == line.PurchaseOrderItemId && i.IsActive)
+                ?? throw new InvalidOperationException($"Purchase order line {line.PurchaseOrderItemId} not found on this Po.");
+
+            if (poItem.IsCancelled)
+                throw new InvalidOperationException($"Line for item {poItem.FK_ItemId} is cancelled and cannot receive stock.");
+
+            if (line.AcceptedQuantity < 0 || line.RejectedQuantity < 0)
+                throw new InvalidOperationException("Accepted/rejected quantities cannot be negative.");
+
+            if (line.AcceptedQuantity + line.RejectedQuantity + poItem.ReceivedQuantity > poItem.Quantity)
+                throw new InvalidOperationException(
+                    $"Accepted + rejected quantity for item {poItem.FK_ItemId} would exceed the ordered quantity.");
+
+            poItem.ReceivedQuantity += line.AcceptedQuantity;
+
+            goodsReceipt.Items.Add(new Models.GoodsReceiptItem
+            {
+                FK_PurchaseOrderItemId = poItem.Id,
+                AcceptedQuantity = line.AcceptedQuantity,
+                RejectedQuantity = line.RejectedQuantity
+            });
+        }
+
+        var activeLines = po.Items.Where(i => i.IsActive && !i.IsCancelled).ToList();
+        po.Status = activeLines.Count > 0 && activeLines.All(i => i.ReceivedQuantity >= i.Quantity)
+            ? PurchaseOrderStatus.Received
+            : PurchaseOrderStatus.PartiallyReceived;
+
+        await uow.BeginAsync(ct);
+        try
+        {
+            await repo.AddAsync(goodsReceipt);
+
+            foreach (var line in goodsReceipt.Items.Where(i => i.AcceptedQuantity > 0))
+            {
+                var poItem = po.Items.First(i => i.Id == line.FK_PurchaseOrderItemId);
+
+                var balance = await stockRepo.GetBalanceAsync(poItem.FK_ItemId, request.WarehouseId);
+                if (balance is null)
+                {
+                    await stockRepo.AddBalanceAsync(new StockBalance
+                    {
+                        FK_ItemId = poItem.FK_ItemId,
+                        LocationId = request.WarehouseId,
+                        LocationType = LocationType.Warehouse,
+                        Quantity = line.AcceptedQuantity
+                    });
+                }
+                else
+                {
+                    balance.Quantity += line.AcceptedQuantity;
+                    balance.UpdatedAt = DateTime.Now;
+                    stockRepo.UpdateBalance(balance);
+                }
+
+                await stockRepo.AddMovementAsync(new StockMovement
+                {
+                    FK_ItemId = poItem.FK_ItemId,
+                    ToLocationId = request.WarehouseId,
+                    ToLocationType = LocationType.Warehouse,
+                    Quantity = line.AcceptedQuantity,
+                    Type = MovementType.PurchaseReceipt,
+                    ReferenceId = goodsReceipt.Id,
+                    CreatedBy = receivedByUserId
+                });
+            }
+
+            poRepo.Update(po);
+            await uow.CommitAsync(ct);
+        }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        var saved = await repo.GetByIdAsync(goodsReceipt.Id);
+        return Map(saved!);
+    }
+}

Distribution/Features/Grn/IGrnRepository.cs

@@ -0,0 +1,14 @@
+namespace Distribution.Features.Grn;
+
+public interface IGrnRepository
+{
+    Task<Models.GoodsReceipt?> GetByIdAsync(Guid id);
+    Task<List<Models.GoodsReceipt>> GetByPurchaseOrderIdAsync(Guid purchaseOrderId);
+    Task AddAsync(Models.GoodsReceipt entity);
+
+    /// <summary>True if at least one GoodsReceipt exists against this Po (createPurchaseReturn guard).</summary>
+    Task<bool> HasAnyForPurchaseOrderAsync(Guid purchaseOrderId);
+
+    /// <summary>Sum of AcceptedQuantity per ItemId across all receipts for a Po.</summary>
+    Task<Dictionary<Guid, int>> GetAcceptedTotalsByItemAsync(Guid purchaseOrderId);
+}

Distribution/Features/Order/OrderService.cs

@@ -1,6 +1,7 @@
 using Distribution.Features.Item;
 using Distribution.Features.PriceList;
 using Distribution.Features.Store;
+using Distribution.Features.Stock;
 using Distribution.Infra.Authorization;
 using Distribution.Infra.UoW;
 using Distribution.Models;
@@ -12,6 +13,7 @@ public class OrderService(
     IOrderRepository repo,
     IStoreRepository storeRepo,
     IItemRepository itemRepo,
+    IStockRepository stockRepo,
     PriceListService priceListService,
     IUnitOfWork uow,
     ICurrentUserService currentUser,
@@ -56,6 +58,19 @@ public class OrderService(
         return requestedUnitPrice.Value;
     }
 
+    /// <summary>
+    /// checkStockAvailability (mainPlan.md §1): confirms the requested quantity does not exceed
+    /// total on-hand stock for the item, summed across every warehouse/vehicle location. Does not
+    /// reserve or decrement stock — actual decrement happens later at loading/delivery time
+    /// (04_loading_event.md / future 05-06 ride execution), not at order placement.
+    /// </summary>
+    private async Task<bool> HasSufficientStockAsync(Guid itemId, decimal quantity)
+    {
+        var balances = await stockRepo.GetBalancesByItemAsync(itemId);
+        var totalAvailable = balances.Sum(b => b.Quantity);
+        return quantity <= totalAvailable;
+    }
+
     public async Task<List<OrderResponse>> GetAllAsync()
     {
         var orders = (await repo.GetAllAsync()).Where(o => o.IsActive).ToList();
@@ -116,6 +131,8 @@ public class OrderService(
         var orderItems = new List<Models.OrderItem>();
         foreach (var i in request.Items)
         {
+            if (!await HasSufficientStockAsync(i.ItemId, i.Quantity)) return null;
+
             var unitPrice = await ResolveUnitPriceAsync(i.ItemId, i.UnitPrice, store, request.OrderDate);
             if (unitPrice is null) return null;
 

Distribution/Features/PurchaseOrder/IPoRepository.cs

@@ -0,0 +1,19 @@
+using Distribution.Models;
+
+namespace Distribution.Features.Po;
+
+public interface IPoRepository
+{
+    Task<Models.PurchaseOrder?> GetByIdAsync(Guid id);
+    Task<List<Models.PurchaseOrder>> GetAllAsync(Guid? supplierId, PurchaseOrderStatus? status);
+    Task AddAsync(Models.PurchaseOrder entity);
+    void Update(Models.PurchaseOrder entity);
+
+    Task AddItemAsync(PurchaseOrderItem entity);
+
+    /// <summary>True if any active (non-cancelled, non-closed-and-void) PurchaseOrder references this supplier.</summary>
+    Task<bool> HasActiveForSupplierAsync(Guid supplierId);
+
+    /// <summary>All active PurchaseOrders for a supplier, with items, used by evaluateSupplier.</summary>
+    Task<List<Models.PurchaseOrder>> GetBySupplierAsync(Guid supplierId);
+}

Distribution/Features/PurchaseOrder/PoController.cs

@@ -0,0 +1,97 @@
+using Distribution.Infra.Authorization;
+using Distribution.Models;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Distribution.Features.Po;
+
+[ApiController]
+[Route("api/purchase-orders")]
+[Authorize]
+public class PoController(PoService service, ICurrentUserService currentUser) : ControllerBase
+{
+    [HttpGet]
+    public async Task<IActionResult> GetAll([FromQuery] Guid? supplierId, [FromQuery] PurchaseOrderStatus? status) =>
+        Ok(await service.GetAllAsync(supplierId, status));
+
+    [HttpGet("{id:guid}")]
+    public async Task<IActionResult> GetById(Guid id)
+    {
+        var result = await service.GetByIdAsync(id);
+        return result is null ? NotFound() : Ok(result);
+    }
+
+    [HttpPost]
+    public async Task<IActionResult> Create(CreatePoRequest request, CancellationToken ct)
+    {
+        var userId = currentUser.UserId ?? throw new UnauthorizedAccessException();
+        try
+        {
+            var result = await service.CreateAsync(request, userId, ct);
+            return CreatedAtAction(nameof(GetById), new { id = result.Id }, result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPut("{id:guid}")]
+    public async Task<IActionResult> Update(Guid id, UpdatePoRequest request, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.UpdateAsync(id, request, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPost("{id:guid}/close")]
+    public async Task<IActionResult> Close(Guid id, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.CloseAsync(id, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPost("{id:guid}/cancel")]
+    public async Task<IActionResult> Cancel(Guid id, CancelPoRequest request, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.CancelAsync(id, request, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPost("{id:guid}/items/{itemId:guid}/cancel")]
+    public async Task<IActionResult> CancelLine(Guid id, Guid itemId, CancelPoLineRequest request, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.CancelLineAsync(id, itemId, request, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPost("{id:guid}/match-invoice")]
+    public async Task<IActionResult> MatchInvoice(Guid id, [FromQuery] Guid? invoiceId, [FromQuery] Guid? grnId)
+    {
+        var result = await service.MatchInvoiceToPoAsync(id, invoiceId, grnId);
+        return result is null ? NotFound() : Ok(result);
+    }
+
+    [HttpPost("{id:guid}/resolve-variance")]
+    public async Task<IActionResult> ResolveVariance(Guid id, ResolveInvoiceVarianceRequest request, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.ResolveInvoiceVarianceAsync(id, request, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+}

Distribution/Features/PurchaseOrder/PoDTOs.cs

@@ -0,0 +1,54 @@
+using Distribution.Models;
+
+namespace Distribution.Features.Po;
+
+public record PoItemRequest(Guid ItemId, int Quantity, decimal UnitCost);
+
+public record CreatePoRequest(Guid SupplierId, List<PoItemRequest> Items);
+
+/// <summary>
+/// Update line: PurchaseOrderItemId set = update an existing unreceived line (Quantity/UnitCost),
+/// null = add a new line to the Po. Only valid while the Po is Issued.
+/// </summary>
+public record UpdatePoLineRequest(Guid? PurchaseOrderItemId, Guid ItemId, int Quantity, decimal UnitCost);
+
+public record UpdatePoRequest(List<UpdatePoLineRequest> Items);
+
+public record CancelPoRequest(string Reason);
+
+public record CancelPoLineRequest(string? Reason);
+
+public record PoItemResponse(
+    Guid Id,
+    Guid ItemId,
+    string Sku,
+    string ItemName,
+    int Quantity,
+    decimal UnitCost,
+    int ReceivedQuantity,
+    int CancelledQuantity,
+    bool IsCancelled);
+
+public record PoResponse(
+    Guid Id,
+    Guid SupplierId,
+    string SupplierName,
+    Guid CreatedByUserId,
+    PurchaseOrderStatus Status,
+    string? CancelReason,
+    bool IsActive,
+    DateTime CreatedAt,
+    List<PoItemResponse> Items);
+
+/// <summary>
+/// Minimal Po-vs-Grn quantity/cost reconciliation. Full 3-way match (Po + Grn + Invoice) activates
+/// once Finance's Invoice entity (step 19, not yet built) exists — until then this compares only
+/// PurchaseOrderItem vs GoodsReceiptItem.
+/// </summary>
+public record InvoiceMatchLineResult(Guid PurchaseOrderItemId, Guid ItemId, int OrderedQuantity, int AcceptedQuantity, decimal UnitCost, bool QuantityMatches);
+
+public record InvoiceMatchResult(Guid PurchaseOrderId, Guid? GoodsReceiptId, Guid? InvoiceId, bool IsMatched, List<InvoiceMatchLineResult> Lines, string Note);
+
+public record ResolveInvoiceVarianceRequest(string Variance, string Resolution, decimal? AdjustedUnitCost, Guid? PurchaseOrderItemId);
+
+public record InvoiceVarianceResolutionResponse(Guid PurchaseOrderId, string Variance, string Resolution, DateTime ResolvedAt);

Distribution/Features/PurchaseOrder/PoRepository.cs

@@ -0,0 +1,49 @@
+using Distribution.Data;
+using Distribution.Models;
+using Microsoft.EntityFrameworkCore;
+
+namespace Distribution.Features.Po;
+
+public class PoRepository(AppDBContext context) : IPoRepository
+{
+    public async Task<Models.PurchaseOrder?> GetByIdAsync(Guid id) =>
+        await context.PurchaseOrders
+            .Include(po => po.Supplier)
+            .Include(po => po.Items).ThenInclude(i => i.Item)
+            .FirstOrDefaultAsync(po => po.Id == id);
+
+    public async Task<List<Models.PurchaseOrder>> GetAllAsync(Guid? supplierId, PurchaseOrderStatus? status)
+    {
+        var query = context.PurchaseOrders
+            .Include(po => po.Supplier)
+            .Include(po => po.Items).ThenInclude(i => i.Item)
+            .Where(po => po.IsActive)
+            .AsQueryable();
+
+        if (supplierId.HasValue) query = query.Where(po => po.FK_SupplierId == supplierId.Value);
+        if (status.HasValue) query = query.Where(po => po.Status == status.Value);
+
+        return await query.OrderByDescending(po => po.CreatedAt).ToListAsync();
+    }
+
+    public async Task AddAsync(Models.PurchaseOrder entity) =>
+        await context.PurchaseOrders.AddAsync(entity);
+
+    public void Update(Models.PurchaseOrder entity) =>
+        context.PurchaseOrders.Update(entity);
+
+    public async Task AddItemAsync(PurchaseOrderItem entity) =>
+        await context.PurchaseOrderItems.AddAsync(entity);
+
+    public async Task<bool> HasActiveForSupplierAsync(Guid supplierId) =>
+        await context.PurchaseOrders.AnyAsync(po =>
+            po.FK_SupplierId == supplierId &&
+            po.IsActive &&
+            po.Status != PurchaseOrderStatus.Cancelled);
+
+    public async Task<List<Models.PurchaseOrder>> GetBySupplierAsync(Guid supplierId) =>
+        await context.PurchaseOrders
+            .Include(po => po.Items)
+            .Where(po => po.FK_SupplierId == supplierId && po.IsActive)
+            .ToListAsync();
+}

Distribution/Features/PurchaseOrder/PoService.cs

@@ -0,0 +1,245 @@
+using Distribution.Features.Grn;
+using Distribution.Infra.UoW;
+using Distribution.Models;
+
+namespace Distribution.Features.Po;
+
+public class PoService(
+    IPoRepository repo,
+    IGrnRepository goodsReceiptRepo,
+    IUnitOfWork uow)
+{
+    private static PoItemResponse MapItem(PurchaseOrderItem i) =>
+        new(i.Id, i.FK_ItemId, i.Item.Sku, i.Item.Name, i.Quantity, i.UnitCost, i.ReceivedQuantity, i.CancelledQuantity, i.IsCancelled);
+
+    private static PoResponse Map(Models.PurchaseOrder po) =>
+        new(po.Id, po.FK_SupplierId, po.Supplier?.Name ?? string.Empty, po.FK_CreatedByUserId,
+            po.Status, po.CancelReason, po.IsActive, po.CreatedAt,
+            po.Items.Where(i => i.IsActive).Select(MapItem).ToList());
+
+    public async Task<List<PoResponse>> GetAllAsync(Guid? supplierId, PurchaseOrderStatus? status) =>
+        (await repo.GetAllAsync(supplierId, status)).Select(Map).ToList();
+
+    public async Task<PoResponse?> GetByIdAsync(Guid id)
+    {
+        var po = await repo.GetByIdAsync(id);
+        if (po is null || !po.IsActive) return null;
+        return Map(po);
+    }
+
+    public async Task<PoResponse> CreateAsync(CreatePoRequest request, Guid createdByUserId, CancellationToken ct = default)
+    {
+        if (request.Items is null || request.Items.Count == 0)
+            throw new InvalidOperationException("A purchase order must have at least one line item.");
+
+        var po = new Models.PurchaseOrder
+        {
+            FK_SupplierId = request.SupplierId,
+            FK_CreatedByUserId = createdByUserId,
+            Status = PurchaseOrderStatus.Issued
+        };
+
+        foreach (var line in request.Items)
+        {
+            po.Items.Add(new PurchaseOrderItem
+            {
+                FK_ItemId = line.ItemId,
+                Quantity = line.Quantity,
+                UnitCost = line.UnitCost
+            });
+        }
+
+        await uow.BeginAsync(ct);
+        try { await repo.AddAsync(po); await uow.CommitAsync(ct); }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return (await GetByIdAsync(po.Id))!;
+    }
+
+    /// <summary>
+    /// May only change unreceived lines (ReceivedQuantity == 0) and only while the Po is Issued.
+    /// Lines with a PurchaseOrderItemId update an existing line; lines without one add a new line.
+    /// </summary>
+    public async Task<PoResponse?> UpdateAsync(Guid id, UpdatePoRequest request, CancellationToken ct = default)
+    {
+        var po = await repo.GetByIdAsync(id);
+        if (po is null || !po.IsActive) return null;
+
+        if (po.Status != PurchaseOrderStatus.Issued)
+            throw new InvalidOperationException($"Cannot update a purchase order in {po.Status} status; only an Issued Po can be updated.");
+
+        await uow.BeginAsync(ct);
+        try
+        {
+            foreach (var line in request.Items)
+            {
+                if (line.PurchaseOrderItemId.HasValue)
+                {
+                    var existing = po.Items.FirstOrDefault(i => i.Id == line.PurchaseOrderItemId.Value && i.IsActive)
+                        ?? throw new InvalidOperationException($"Purchase order line {line.PurchaseOrderItemId} not found on this Po.");
+
+                    if (existing.ReceivedQuantity > 0)
+                        throw new InvalidOperationException(
+                            $"Line for item {existing.FK_ItemId} has already received stock and cannot be edited; use cancelPurchaseOrderLine or createPurchaseReturn instead.");
+
+                    existing.FK_ItemId = line.ItemId;
+                    existing.Quantity = line.Quantity;
+                    existing.UnitCost = line.UnitCost;
+                }
+                else
+                {
+                    await repo.AddItemAsync(new PurchaseOrderItem
+                    {
+                        FK_PurchaseOrderId = po.Id,
+                        FK_ItemId = line.ItemId,
+                        Quantity = line.Quantity,
+                        UnitCost = line.UnitCost
+                    });
+                }
+            }
+
+            repo.Update(po);
+            await uow.CommitAsync(ct);
+        }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return (await GetByIdAsync(id))!;
+    }
+
+    /// <summary>
+    /// Only valid once a Po is Received, or manually closed early (outstanding quantity written off).
+    /// </summary>
+    public async Task<PoResponse?> CloseAsync(Guid id, CancellationToken ct = default)
+    {
+        var po = await repo.GetByIdAsync(id);
+        if (po is null || !po.IsActive) return null;
+
+        if (po.Status is PurchaseOrderStatus.Closed or PurchaseOrderStatus.Cancelled)
+            throw new InvalidOperationException($"Cannot close a purchase order already in {po.Status} status.");
+
+        po.Status = PurchaseOrderStatus.Closed;
+
+        await uow.BeginAsync(ct);
+        try { repo.Update(po); await uow.CommitAsync(ct); }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return Map(po);
+    }
+
+    /// <summary>Only valid before any goods receipt exists against the Po.</summary>
+    public async Task<PoResponse?> CancelAsync(Guid id, CancelPoRequest request, CancellationToken ct = default)
+    {
+        var po = await repo.GetByIdAsync(id);
+        if (po is null || !po.IsActive) return null;
+
+        if (po.Status is PurchaseOrderStatus.Closed or PurchaseOrderStatus.Cancelled)
+            throw new InvalidOperationException($"Cannot cancel a purchase order already in {po.Status} status.");
+
+        if (await goodsReceiptRepo.HasAnyForPurchaseOrderAsync(id))
+            throw new InvalidOperationException("Cannot cancel a purchase order that already has a goods receipt against it.");
+
+        po.Status = PurchaseOrderStatus.Cancelled;
+        po.CancelReason = request.Reason;
+
+        await uow.BeginAsync(ct);
+        try { repo.Update(po); await uow.CommitAsync(ct); }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return Map(po);
+    }
+
+    /// <summary>
+    /// Cancels a single line instead of the whole Po. Only valid while ReceivedQuantity &lt; Quantity
+    /// and the line isn't already fully received or cancelled. Auto-completes the Po to Received once
+    /// every non-cancelled line is fully received.
+    /// </summary>
+    public async Task<PoResponse?> CancelLineAsync(Guid id, Guid poItemId, CancelPoLineRequest request, CancellationToken ct = default)
+    {
+        var po = await repo.GetByIdAsync(id);
+        if (po is null || !po.IsActive) return null;
+
+        var line = po.Items.FirstOrDefault(i => i.Id == poItemId && i.IsActive)
+            ?? throw new InvalidOperationException("Purchase order line not found on this Po.");
+
+        if (line.IsCancelled)
+            throw new InvalidOperationException("This line is already cancelled.");
+
+        if (line.ReceivedQuantity >= line.Quantity)
+            throw new InvalidOperationException("This line is already fully received and cannot be cancelled.");
+
+        line.IsCancelled = true;
+        line.CancelledQuantity = line.Quantity - line.ReceivedQuantity;
+
+        var activeLines = po.Items.Where(i => i.IsActive).ToList();
+        if (activeLines.Where(i => !i.IsCancelled).All(i => i.ReceivedQuantity >= i.Quantity)
+            && activeLines.Any(i => !i.IsCancelled))
+        {
+            po.Status = PurchaseOrderStatus.Received;
+        }
+
+        await uow.BeginAsync(ct);
+        try { repo.Update(po); await uow.CommitAsync(ct); }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return Map(po);
+    }
+
+    /// <summary>
+    /// Minimal Po-vs-Grn reconciliation (matchInvoiceToPo). Full 3-way match against an Invoice
+    /// entity activates once Finance (step 19) exists; this only detects and reports, never adjusts.
+    /// </summary>
+    public async Task<InvoiceMatchResult?> MatchInvoiceToPoAsync(Guid poId, Guid? invoiceId, Guid? grnId)
+    {
+        var po = await repo.GetByIdAsync(poId);
+        if (po is null || !po.IsActive) return null;
+
+        var receipts = grnId.HasValue
+            ? (await goodsReceiptRepo.GetByPurchaseOrderIdAsync(poId)).Where(g => g.Id == grnId.Value).ToList()
+            : await goodsReceiptRepo.GetByPurchaseOrderIdAsync(poId);
+
+        var acceptedByItem = receipts
+            .SelectMany(g => g.Items.Where(i => i.IsActive))
+            .GroupBy(i => i.PurchaseOrderItem.FK_ItemId)
+            .ToDictionary(g => g.Key, g => g.Sum(i => i.AcceptedQuantity));
+
+        var lines = po.Items.Where(i => i.IsActive).Select(i =>
+        {
+            acceptedByItem.TryGetValue(i.FK_ItemId, out var accepted);
+            return new InvoiceMatchLineResult(i.Id, i.FK_ItemId, i.Quantity, accepted, i.UnitCost, accepted == i.Quantity);
+        }).ToList();
+
+        var isMatched = lines.All(l => l.QuantityMatches);
+
+        return new InvoiceMatchResult(
+            poId, grnId, invoiceId, isMatched, lines,
+            "Compares PurchaseOrderItem.Quantity against GoodsReceiptItem.AcceptedQuantity only; " +
+            "invoice line comparison activates once Finance's Invoice entity (step 19) exists.");
+    }
+
+    /// <summary>
+    /// Records a Po/Grn(/invoice) variance and its resolution. Never silently adjusts anything except
+    /// when the resolution explicitly requests a retroactive UnitCost adjustment on a named line.
+    /// </summary>
+    public async Task<InvoiceVarianceResolutionResponse?> ResolveInvoiceVarianceAsync(Guid poId, ResolveInvoiceVarianceRequest request, CancellationToken ct = default)
+    {
+        var po = await repo.GetByIdAsync(poId);
+        if (po is null || !po.IsActive) return null;
+
+        if (request.AdjustedUnitCost.HasValue)
+        {
+            if (!request.PurchaseOrderItemId.HasValue)
+                throw new InvalidOperationException("PurchaseOrderItemId is required when adjusting UnitCost.");
+
+            var line = po.Items.FirstOrDefault(i => i.Id == request.PurchaseOrderItemId.Value && i.IsActive)
+                ?? throw new InvalidOperationException("Purchase order line not found on this Po.");
+
+            line.UnitCost = request.AdjustedUnitCost.Value;
+
+            await uow.BeginAsync(ct);
+            try { repo.Update(po); await uow.CommitAsync(ct); }
+            catch { await uow.RollbackAsync(ct); throw; }
+        }
+
+        return new InvoiceVarianceResolutionResponse(poId, request.Variance, request.Resolution, DateTime.Now);
+    }
+}

Distribution/Features/PurchaseReturn/IPurchaseReturnRepository.cs

@@ -0,0 +1,11 @@
+namespace Distribution.Features.PurchaseReturn;
+
+public interface IPurchaseReturnRepository
+{
+    Task<Models.PurchaseReturn?> GetByIdAsync(Guid id);
+    Task<List<Models.PurchaseReturn>> GetByPurchaseOrderIdAsync(Guid purchaseOrderId);
+    Task AddAsync(Models.PurchaseReturn entity);
+
+    /// <summary>Sum of Quantity per ItemId across all prior returns for a Po.</summary>
+    Task<Dictionary<Guid, int>> GetReturnedTotalsByItemAsync(Guid purchaseOrderId);
+}

Distribution/Features/PurchaseReturn/PurchaseReturnController.cs

@@ -0,0 +1,33 @@
+using Distribution.Infra.Authorization;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Distribution.Features.PurchaseReturn;
+
+[ApiController]
+[Authorize]
+public class PurchaseReturnController(PurchaseReturnService service, ICurrentUserService currentUser) : ControllerBase
+{
+    [HttpGet("api/purchase-returns/{id:guid}")]
+    public async Task<IActionResult> GetById(Guid id)
+    {
+        var result = await service.GetByIdAsync(id);
+        return result is null ? NotFound() : Ok(result);
+    }
+
+    [HttpGet("api/purchase-orders/{id:guid}/returns")]
+    public async Task<IActionResult> GetByPurchaseOrder(Guid id) =>
+        Ok(await service.GetByPurchaseOrderIdAsync(id));
+
+    [HttpPost("api/purchase-orders/{id:guid}/returns")]
+    public async Task<IActionResult> Create(Guid id, CreatePurchaseReturnRequest request, CancellationToken ct)
+    {
+        var userId = currentUser.UserId ?? throw new UnauthorizedAccessException();
+        try
+        {
+            var result = await service.CreateAsync(id, request, userId, ct);
+            return CreatedAtAction(nameof(GetById), new { id = result.Id }, result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+}

Distribution/Features/PurchaseReturn/PurchaseReturnDTOs.cs

@@ -0,0 +1,15 @@
+namespace Distribution.Features.PurchaseReturn;
+
+public record PurchaseReturnItemRequest(Guid ItemId, int Quantity);
+
+public record CreatePurchaseReturnRequest(string Reason, List<PurchaseReturnItemRequest> Items);
+
+public record PurchaseReturnItemResponse(Guid Id, Guid ItemId, string Sku, string ItemName, int Quantity);
+
+public record PurchaseReturnResponse(
+    Guid Id,
+    Guid PurchaseOrderId,
+    string Reason,
+    bool IsActive,
+    DateTime CreatedAt,
+    List<PurchaseReturnItemResponse> Items);

Distribution/Features/PurchaseReturn/PurchaseReturnRepository.cs

@@ -0,0 +1,30 @@
+using Distribution.Data;
+using Microsoft.EntityFrameworkCore;
+
+namespace Distribution.Features.PurchaseReturn;
+
+public class PurchaseReturnRepository(AppDBContext context) : IPurchaseReturnRepository
+{
+    public async Task<Models.PurchaseReturn?> GetByIdAsync(Guid id) =>
+        await context.PurchaseReturns
+            .Include(pr => pr.Items).ThenInclude(i => i.Item)
+            .FirstOrDefaultAsync(pr => pr.Id == id);
+
+    public async Task<List<Models.PurchaseReturn>> GetByPurchaseOrderIdAsync(Guid purchaseOrderId) =>
+        await context.PurchaseReturns
+            .Include(pr => pr.Items).ThenInclude(i => i.Item)
+            .Where(pr => pr.FK_PurchaseOrderId == purchaseOrderId && pr.IsActive)
+            .OrderByDescending(pr => pr.CreatedAt)
+            .ToListAsync();
+
+    public async Task AddAsync(Models.PurchaseReturn entity) =>
+        await context.PurchaseReturns.AddAsync(entity);
+
+    public async Task<Dictionary<Guid, int>> GetReturnedTotalsByItemAsync(Guid purchaseOrderId) =>
+        await context.PurchaseReturnItems
+            .Include(i => i.PurchaseReturn)
+            .Where(i => i.PurchaseReturn.FK_PurchaseOrderId == purchaseOrderId && i.IsActive)
+            .GroupBy(i => i.FK_ItemId)
+            .Select(g => new { ItemId = g.Key, Total = g.Sum(i => i.Quantity) })
+            .ToDictionaryAsync(x => x.ItemId, x => x.Total);
+}

Distribution/Features/PurchaseReturn/PurchaseReturnService.cs

@@ -0,0 +1,122 @@
+using Distribution.Features.Grn;
+using Distribution.Features.Po;
+using Distribution.Features.Stock;
+using Distribution.Infra.UoW;
+using Distribution.Models;
+
+namespace Distribution.Features.PurchaseReturn;
+
+public class PurchaseReturnService(
+    IPurchaseReturnRepository repo,
+    IPoRepository poRepo,
+    IGrnRepository goodsReceiptRepo,
+    IStockRepository stockRepo,
+    IUnitOfWork uow)
+{
+    private static PurchaseReturnItemResponse MapItem(Models.PurchaseReturnItem i) =>
+        new(i.Id, i.FK_ItemId, i.Item.Sku, i.Item.Name, i.Quantity);
+
+    private static PurchaseReturnResponse Map(Models.PurchaseReturn pr) =>
+        new(pr.Id, pr.FK_PurchaseOrderId, pr.Reason, pr.IsActive, pr.CreatedAt,
+            pr.Items.Where(i => i.IsActive).Select(MapItem).ToList());
+
+    public async Task<PurchaseReturnResponse?> GetByIdAsync(Guid id)
+    {
+        var pr = await repo.GetByIdAsync(id);
+        if (pr is null || !pr.IsActive) return null;
+        return Map(pr);
+    }
+
+    public async Task<List<PurchaseReturnResponse>> GetByPurchaseOrderIdAsync(Guid purchaseOrderId) =>
+        (await repo.GetByPurchaseOrderIdAsync(purchaseOrderId)).Select(Map).ToList();
+
+    /// <summary>
+    /// Requires at least one prior GoodsReceipt against the Po; return quantities per item cannot
+    /// exceed the received-but-not-already-returned quantity for that item. Decrements StockBalance
+    /// and writes a StockMovement in the same unit of work.
+    /// </summary>
+    public async Task<PurchaseReturnResponse> CreateAsync(Guid purchaseOrderId, CreatePurchaseReturnRequest request, Guid createdByUserId, CancellationToken ct = default)
+    {
+        var po = await poRepo.GetByIdAsync(purchaseOrderId);
+        if (po is null || !po.IsActive)
+            throw new InvalidOperationException("Purchase order not found.");
+
+        if (!await goodsReceiptRepo.HasAnyForPurchaseOrderAsync(purchaseOrderId))
+            throw new InvalidOperationException("Cannot return items for a purchase order with no goods receipt against it.");
+
+        if (request.Items is null || request.Items.Count == 0)
+            throw new InvalidOperationException("A purchase return must have at least one line item.");
+
+        var receivedTotals = await goodsReceiptRepo.GetAcceptedTotalsByItemAsync(purchaseOrderId);
+        var returnedTotals = await repo.GetReturnedTotalsByItemAsync(purchaseOrderId);
+
+        // The receipt(s) for this Po share a single receiving warehouse per the current model
+        // (each GoodsReceipt carries FK_WarehouseId); use the most recent receipt's warehouse
+        // as the stock-decrement location for the return.
+        var receipts = await goodsReceiptRepo.GetByPurchaseOrderIdAsync(purchaseOrderId);
+        var warehouseId = receipts.First().FK_WarehouseId;
+
+        var purchaseReturn = new Models.PurchaseReturn
+        {
+            FK_PurchaseOrderId = purchaseOrderId,
+            Reason = request.Reason
+        };
+
+        foreach (var line in request.Items)
+        {
+            if (line.Quantity <= 0)
+                throw new InvalidOperationException("Return quantity must be greater than zero.");
+
+            receivedTotals.TryGetValue(line.ItemId, out var received);
+            returnedTotals.TryGetValue(line.ItemId, out var alreadyReturned);
+            var available = received - alreadyReturned;
+
+            if (line.Quantity > available)
+                throw new InvalidOperationException(
+                    $"Return quantity for item {line.ItemId} ({line.Quantity}) exceeds the received-but-not-already-returned quantity ({available}).");
+
+            purchaseReturn.Items.Add(new Models.PurchaseReturnItem
+            {
+                FK_ItemId = line.ItemId,
+                Quantity = line.Quantity
+            });
+        }
+
+        await uow.BeginAsync(ct);
+        try
+        {
+            await repo.AddAsync(purchaseReturn);
+
+            foreach (var line in purchaseReturn.Items)
+            {
+                var balance = await stockRepo.GetBalanceAsync(line.FK_ItemId, warehouseId)
+                    ?? throw new InvalidOperationException($"No stock balance found for item {line.FK_ItemId} at the receiving warehouse.");
+
+                if (balance.Quantity < line.Quantity)
+                    throw new InvalidOperationException($"Insufficient warehouse stock for item {line.FK_ItemId} to return.");
+
+                balance.Quantity -= line.Quantity;
+                balance.UpdatedAt = DateTime.Now;
+                stockRepo.UpdateBalance(balance);
+
+                await stockRepo.AddMovementAsync(new StockMovement
+                {
+                    FK_ItemId = line.FK_ItemId,
+                    FromLocationId = warehouseId,
+                    FromLocationType = LocationType.Warehouse,
+                    Quantity = line.Quantity,
+                    Type = MovementType.PurchaseReturn,
+                    ReasonCode = request.Reason,
+                    ReferenceId = purchaseReturn.Id,
+                    CreatedBy = createdByUserId
+                });
+            }
+
+            await uow.CommitAsync(ct);
+        }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        var saved = await repo.GetByIdAsync(purchaseReturn.Id);
+        return Map(saved!);
+    }
+}

Distribution/Features/Supplier/SupplierController.cs

@@ -36,7 +36,18 @@ public class SupplierController(SupplierService service) : ControllerBase
     [HttpDelete("{id:guid}")]
     public async Task<IActionResult> Delete(Guid id, CancellationToken ct)
     {
-        var deleted = await service.DeleteAsync(id, ct);
-        return deleted ? NoContent() : NotFound();
+        try
+        {
+            var deleted = await service.DeleteAsync(id, ct);
+            return deleted ? NoContent() : NotFound();
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPost("{id:guid}/evaluate")]
+    public async Task<IActionResult> Evaluate(Guid id, CancellationToken ct)
+    {
+        var result = await service.EvaluateAsync(id, ct);
+        return result is null ? NotFound() : Ok(result);
     }
 }

Distribution/Features/Supplier/SupplierService.cs

@@ -1,8 +1,14 @@
+using Distribution.Features.Grn;
+using Distribution.Features.Po;
 using Distribution.Infra.UoW;
 
 namespace Distribution.Features.Supplier;
 
-public class SupplierService(ISupplierRepository repo, IUnitOfWork uow)
+public class SupplierService(
+    ISupplierRepository repo,
+    IPoRepository purchaseOrderRepo,
+    IGrnRepository goodsReceiptRepo,
+    IUnitOfWork uow)
 {
     private static SupplierResponse Map(Models.Supplier s) =>
         new(s.Id, s.Name, s.ContactInfo, s.PerformanceScore, s.IsActive, s.CreatedAt);
@@ -52,10 +58,83 @@ public class SupplierService(ISupplierRepository repo, IUnitOfWork uow)
         var supplier = await repo.GetByIdAsync(id);
         if (supplier is null || !supplier.IsActive) return false;
 
+        if (await purchaseOrderRepo.HasActiveForSupplierAsync(id))
+            throw new InvalidOperationException(
+                "Cannot delete a supplier that is referenced by an active purchase order.");
+
         await uow.BeginAsync(ct);
         try { repo.Remove(supplier); await uow.CommitAsync(ct); }
         catch { await uow.RollbackAsync(ct); throw; }
 
         return true;
     }
+
+    /// <summary>
+    /// The only writer of Supplier.PerformanceScore. Computes a simple 0-100 score from this
+    /// supplier's own purchase-order history:
+    ///   - lineFulfillmentRatio: received (non-cancelled, fully-received) Po lines / all non-active
+    ///     Po lines seen (received + cancelled) - how reliably the supplier fulfils what it commits to.
+    ///   - acceptanceRatio: AcceptedQuantity / (AcceptedQuantity + RejectedQuantity) across every
+    ///     GoodsReceipt against this supplier's Pos - how much of what arrives is usable.
+    /// score = round(average(lineFulfillmentRatio, acceptanceRatio) * 100, 2).
+    /// Defaults to 50 (neutral) when there is no history yet, rather than hardcoding a fixed score.
+    /// </summary>
+    public async Task<SupplierResponse?> EvaluateAsync(Guid id, CancellationToken ct = default)
+    {
+        var supplier = await repo.GetByIdAsync(id);
+        if (supplier is null || !supplier.IsActive) return null;
+
+        var purchaseOrders = await purchaseOrderRepo.GetBySupplierAsync(id);
+
+        var receivedLines = 0;
+        var cancelledLines = 0;
+        foreach (var po in purchaseOrders)
+        {
+            foreach (var item in po.Items.Where(i => i.IsActive))
+            {
+                if (item.IsCancelled) cancelledLines++;
+                else if (item.ReceivedQuantity >= item.Quantity) receivedLines++;
+            }
+        }
+
+        var totalAccepted = 0;
+        var totalRejected = 0;
+        foreach (var po in purchaseOrders)
+        {
+            foreach (var receipt in await goodsReceiptRepo.GetByPurchaseOrderIdAsync(po.Id))
+            {
+                foreach (var item in receipt.Items.Where(i => i.IsActive))
+                {
+                    totalAccepted += item.AcceptedQuantity;
+                    totalRejected += item.RejectedQuantity;
+                }
+            }
+        }
+
+        var lineFulfillmentRatio = receivedLines + cancelledLines > 0
+            ? (decimal)receivedLines / (receivedLines + cancelledLines)
+            : (decimal?)null;
+
+        var acceptanceRatio = totalAccepted + totalRejected > 0
+            ? (decimal)totalAccepted / (totalAccepted + totalRejected)
+            : (decimal?)null;
+
+        decimal score;
+        if (lineFulfillmentRatio.HasValue && acceptanceRatio.HasValue)
+            score = Math.Round((lineFulfillmentRatio.Value + acceptanceRatio.Value) / 2m * 100m, 2);
+        else if (lineFulfillmentRatio.HasValue)
+            score = Math.Round(lineFulfillmentRatio.Value * 100m, 2);
+        else if (acceptanceRatio.HasValue)
+            score = Math.Round(acceptanceRatio.Value * 100m, 2);
+        else
+            score = 50m;
+
+        supplier.PerformanceScore = score;
+
+        await uow.BeginAsync(ct);
+        try { repo.Update(supplier); await uow.CommitAsync(ct); }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return Map(supplier);
+    }
 }

Distribution/Migrations/20260824110925_AddProcurement.cs

@@ -0,0 +1,257 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Distribution.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddProcurement : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "PurchaseOrders",
+                columns: table => new
+                {
+                    Id = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_SupplierId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_CreatedByUserId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    Status = table.Column<int>(type: "int", nullable: false),
+                    CancelReason = table.Column<string>(type: "longtext", nullable: true)
+                        .Annotation("MySql:CharSet", "utf8mb4"),
+                    CreatedAt = table.Column<DateTime>(type: "datetime(6)", nullable: false),
+                    IsActive = table.Column<bool>(type: "tinyint(1)", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_PurchaseOrders", x => x.Id);
+                    table.ForeignKey(
+                        name: "FK_PurchaseOrders_Suppliers_FK_SupplierId",
+                        column: x => x.FK_SupplierId,
+                        principalTable: "Suppliers",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Restrict);
+                })
+                .Annotation("MySql:CharSet", "utf8mb4");
+
+            migrationBuilder.CreateTable(
+                name: "GoodsReceipts",
+                columns: table => new
+                {
+                    Id = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_PurchaseOrderId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_ReceivedByUserId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_WarehouseId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    ReceivedAt = table.Column<DateTime>(type: "datetime(6)", nullable: false),
+                    CreatedAt = table.Column<DateTime>(type: "datetime(6)", nullable: false),
+                    IsActive = table.Column<bool>(type: "tinyint(1)", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_GoodsReceipts", x => x.Id);
+                    table.ForeignKey(
+                        name: "FK_GoodsReceipts_PurchaseOrders_FK_PurchaseOrderId",
+                        column: x => x.FK_PurchaseOrderId,
+                        principalTable: "PurchaseOrders",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Restrict);
+                    table.ForeignKey(
+                        name: "FK_GoodsReceipts_Warehouses_FK_WarehouseId",
+                        column: x => x.FK_WarehouseId,
+                        principalTable: "Warehouses",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Restrict);
+                })
+                .Annotation("MySql:CharSet", "utf8mb4");
+
+            migrationBuilder.CreateTable(
+                name: "PurchaseOrderItems",
+                columns: table => new
+                {
+                    Id = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_PurchaseOrderId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_ItemId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    Quantity = table.Column<int>(type: "int", nullable: false),
+                    UnitCost = table.Column<decimal>(type: "decimal(65,30)", nullable: false),
+                    ReceivedQuantity = table.Column<int>(type: "int", nullable: false),
+                    CancelledQuantity = table.Column<int>(type: "int", nullable: false),
+                    IsCancelled = table.Column<bool>(type: "tinyint(1)", nullable: false),
+                    CreatedAt = table.Column<DateTime>(type: "datetime(6)", nullable: false),
+                    IsActive = table.Column<bool>(type: "tinyint(1)", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_PurchaseOrderItems", x => x.Id);
+                    table.ForeignKey(
+                        name: "FK_PurchaseOrderItems_Items_FK_ItemId",
+                        column: x => x.FK_ItemId,
+                        principalTable: "Items",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Restrict);
+                    table.ForeignKey(
+                        name: "FK_PurchaseOrderItems_PurchaseOrders_FK_PurchaseOrderId",
+                        column: x => x.FK_PurchaseOrderId,
+                        principalTable: "PurchaseOrders",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Restrict);
+                })
+                .Annotation("MySql:CharSet", "utf8mb4");
+
+            migrationBuilder.CreateTable(
+                name: "PurchaseReturns",
+                columns: table => new
+                {
+                    Id = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_PurchaseOrderId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    Reason = table.Column<string>(type: "longtext", nullable: false)
+                        .Annotation("MySql:CharSet", "utf8mb4"),
+                    CreatedAt = table.Column<DateTime>(type: "datetime(6)", nullable: false),
+                    IsActive = table.Column<bool>(type: "tinyint(1)", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_PurchaseReturns", x => x.Id);
+                    table.ForeignKey(
+                        name: "FK_PurchaseReturns_PurchaseOrders_FK_PurchaseOrderId",
+                        column: x => x.FK_PurchaseOrderId,
+                        principalTable: "PurchaseOrders",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Restrict);
+                })
+                .Annotation("MySql:CharSet", "utf8mb4");
+
+            migrationBuilder.CreateTable(
+                name: "GoodsReceiptItems",
+                columns: table => new
+                {
+                    Id = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_GoodsReceiptId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_PurchaseOrderItemId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    AcceptedQuantity = table.Column<int>(type: "int", nullable: false),
+                    RejectedQuantity = table.Column<int>(type: "int", nullable: false),
+                    CreatedAt = table.Column<DateTime>(type: "datetime(6)", nullable: false),
+                    IsActive = table.Column<bool>(type: "tinyint(1)", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_GoodsReceiptItems", x => x.Id);
+                    table.ForeignKey(
+                        name: "FK_GoodsReceiptItems_GoodsReceipts_FK_GoodsReceiptId",
+                        column: x => x.FK_GoodsReceiptId,
+                        principalTable: "GoodsReceipts",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Restrict);
+                    table.ForeignKey(
+                        name: "FK_GoodsReceiptItems_PurchaseOrderItems_FK_PurchaseOrderItemId",
+                        column: x => x.FK_PurchaseOrderItemId,
+                        principalTable: "PurchaseOrderItems",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Restrict);
+                })
+                .Annotation("MySql:CharSet", "utf8mb4");
+
+            migrationBuilder.CreateTable(
+                name: "PurchaseReturnItems",
+                columns: table => new
+                {
+                    Id = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_PurchaseReturnId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    FK_ItemId = table.Column<Guid>(type: "char(36)", nullable: false, collation: "ascii_general_ci"),
+                    Quantity = table.Column<int>(type: "int", nullable: false),
+                    CreatedAt = table.Column<DateTime>(type: "datetime(6)", nullable: false),
+                    IsActive = table.Column<bool>(type: "tinyint(1)", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_PurchaseReturnItems", x => x.Id);
+                    table.ForeignKey(
+                        name: "FK_PurchaseReturnItems_Items_FK_ItemId",
+                        column: x => x.FK_ItemId,
+                        principalTable: "Items",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Restrict);
+                    table.ForeignKey(
+                        name: "FK_PurchaseReturnItems_PurchaseReturns_FK_PurchaseReturnId",
+                        column: x => x.FK_PurchaseReturnId,
+                        principalTable: "PurchaseReturns",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Restrict);
+                })
+                .Annotation("MySql:CharSet", "utf8mb4");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_GoodsReceiptItems_FK_GoodsReceiptId",
+                table: "GoodsReceiptItems",
+                column: "FK_GoodsReceiptId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_GoodsReceiptItems_FK_PurchaseOrderItemId",
+                table: "GoodsReceiptItems",
+                column: "FK_PurchaseOrderItemId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_GoodsReceipts_FK_PurchaseOrderId",
+                table: "GoodsReceipts",
+                column: "FK_PurchaseOrderId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_GoodsReceipts_FK_WarehouseId",
+                table: "GoodsReceipts",
+                column: "FK_WarehouseId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_PurchaseOrderItems_FK_ItemId",
+                table: "PurchaseOrderItems",
+                column: "FK_ItemId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_PurchaseOrderItems_FK_PurchaseOrderId",
+                table: "PurchaseOrderItems",
+                column: "FK_PurchaseOrderId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_PurchaseOrders_FK_SupplierId",
+                table: "PurchaseOrders",
+                column: "FK_SupplierId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_PurchaseReturnItems_FK_ItemId",
+                table: "PurchaseReturnItems",
+                column: "FK_ItemId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_PurchaseReturnItems_FK_PurchaseReturnId",
+                table: "PurchaseReturnItems",
+                column: "FK_PurchaseReturnId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_PurchaseReturns_FK_PurchaseOrderId",
+                table: "PurchaseReturns",
+                column: "FK_PurchaseOrderId");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "GoodsReceiptItems");
+
+            migrationBuilder.DropTable(
+                name: "PurchaseReturnItems");
+
+            migrationBuilder.DropTable(
+                name: "GoodsReceipts");
+
+            migrationBuilder.DropTable(
+                name: "PurchaseOrderItems");
+
+            migrationBuilder.DropTable(
+                name: "PurchaseReturns");
+
+            migrationBuilder.DropTable(
+                name: "PurchaseOrders");
+        }
+    }
+}

Distribution/Migrations/AppDBContextModelSnapshot.cs

@@ -187,6 +187,72 @@ namespace Distribution.Migrations
                     b.ToTable("DriverProfiles");
                 });
 
+            modelBuilder.Entity("Distribution.Models.GoodsReceipt", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("char(36)");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.Property<Guid>("FK_PurchaseOrderId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<Guid>("FK_ReceivedByUserId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<Guid>("FK_WarehouseId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<bool>("IsActive")
+                        .HasColumnType("tinyint(1)");
+
+                    b.Property<DateTime>("ReceivedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("FK_PurchaseOrderId");
+
+                    b.HasIndex("FK_WarehouseId");
+
+                    b.ToTable("GoodsReceipts");
+                });
+
+            modelBuilder.Entity("Distribution.Models.GoodsReceiptItem", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("char(36)");
+
+                    b.Property<int>("AcceptedQuantity")
+                        .HasColumnType("int");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.Property<Guid>("FK_GoodsReceiptId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<Guid>("FK_PurchaseOrderItemId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<bool>("IsActive")
+                        .HasColumnType("tinyint(1)");
+
+                    b.Property<int>("RejectedQuantity")
+                        .HasColumnType("int");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("FK_GoodsReceiptId");
+
+                    b.HasIndex("FK_PurchaseOrderItemId");
+
+                    b.ToTable("GoodsReceiptItems");
+                });
+
             modelBuilder.Entity("Distribution.Models.Item", b =>
                 {
                     b.Property<Guid>("Id")
@@ -471,6 +537,135 @@ namespace Distribution.Migrations
                     b.ToTable("PriceListItems");
                 });
 
+            modelBuilder.Entity("Distribution.Models.PurchaseOrder", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("char(36)");
+
+                    b.Property<string>("CancelReason")
+                        .HasColumnType("longtext");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.Property<Guid>("FK_CreatedByUserId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<Guid>("FK_SupplierId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<bool>("IsActive")
+                        .HasColumnType("tinyint(1)");
+
+                    b.Property<int>("Status")
+                        .HasColumnType("int");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("FK_SupplierId");
+
+                    b.ToTable("PurchaseOrders");
+                });
+
+            modelBuilder.Entity("Distribution.Models.PurchaseOrderItem", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("char(36)");
+
+                    b.Property<int>("CancelledQuantity")
+                        .HasColumnType("int");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.Property<Guid>("FK_ItemId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<Guid>("FK_PurchaseOrderId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<bool>("IsActive")
+                        .HasColumnType("tinyint(1)");
+
+                    b.Property<bool>("IsCancelled")
+                        .HasColumnType("tinyint(1)");
+
+                    b.Property<int>("Quantity")
+                        .HasColumnType("int");
+
+                    b.Property<int>("ReceivedQuantity")
+                        .HasColumnType("int");
+
+                    b.Property<decimal>("UnitCost")
+                        .HasColumnType("decimal(65,30)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("FK_ItemId");
+
+                    b.HasIndex("FK_PurchaseOrderId");
+
+                    b.ToTable("PurchaseOrderItems");
+                });
+
+            modelBuilder.Entity("Distribution.Models.PurchaseReturn", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("char(36)");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.Property<Guid>("FK_PurchaseOrderId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<bool>("IsActive")
+                        .HasColumnType("tinyint(1)");
+
+                    b.Property<string>("Reason")
+                        .IsRequired()
+                        .HasColumnType("longtext");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("FK_PurchaseOrderId");
+
+                    b.ToTable("PurchaseReturns");
+                });
+
+            modelBuilder.Entity("Distribution.Models.PurchaseReturnItem", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("char(36)");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.Property<Guid>("FK_ItemId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<Guid>("FK_PurchaseReturnId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<bool>("IsActive")
+                        .HasColumnType("tinyint(1)");
+
+                    b.Property<int>("Quantity")
+                        .HasColumnType("int");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("FK_ItemId");
+
+                    b.HasIndex("FK_PurchaseReturnId");
+
+                    b.ToTable("PurchaseReturnItems");
+                });
+
             modelBuilder.Entity("Distribution.Models.Region", b =>
                 {
                     b.Property<Guid>("Id")
@@ -1315,6 +1510,44 @@ namespace Distribution.Migrations
                     b.Navigation("User");
                 });
 
+            modelBuilder.Entity("Distribution.Models.GoodsReceipt", b =>
+                {
+                    b.HasOne("Distribution.Models.PurchaseOrder", "PurchaseOrder")
+                        .WithMany()
+                        .HasForeignKey("FK_PurchaseOrderId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.HasOne("Distribution.Models.Warehouse", "Warehouse")
+                        .WithMany()
+                        .HasForeignKey("FK_WarehouseId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("PurchaseOrder");
+
+                    b.Navigation("Warehouse");
+                });
+
+            modelBuilder.Entity("Distribution.Models.GoodsReceiptItem", b =>
+                {
+                    b.HasOne("Distribution.Models.GoodsReceipt", "GoodsReceipt")
+                        .WithMany("Items")
+                        .HasForeignKey("FK_GoodsReceiptId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.HasOne("Distribution.Models.PurchaseOrderItem", "PurchaseOrderItem")
+                        .WithMany()
+                        .HasForeignKey("FK_PurchaseOrderItemId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("GoodsReceipt");
+
+                    b.Navigation("PurchaseOrderItem");
+                });
+
             modelBuilder.Entity("Distribution.Models.Item", b =>
                 {
                     b.HasOne("Distribution.Models.Uom", "BaseUom")
@@ -1442,6 +1675,66 @@ namespace Distribution.Migrations
                     b.Navigation("PriceList");
                 });
 
+            modelBuilder.Entity("Distribution.Models.PurchaseOrder", b =>
+                {
+                    b.HasOne("Distribution.Models.Supplier", "Supplier")
+                        .WithMany()
+                        .HasForeignKey("FK_SupplierId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("Supplier");
+                });
+
+            modelBuilder.Entity("Distribution.Models.PurchaseOrderItem", b =>
+                {
+                    b.HasOne("Distribution.Models.Item", "Item")
+                        .WithMany()
+                        .HasForeignKey("FK_ItemId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.HasOne("Distribution.Models.PurchaseOrder", "PurchaseOrder")
+                        .WithMany("Items")
+                        .HasForeignKey("FK_PurchaseOrderId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("Item");
+
+                    b.Navigation("PurchaseOrder");
+                });
+
+            modelBuilder.Entity("Distribution.Models.PurchaseReturn", b =>
+                {
+                    b.HasOne("Distribution.Models.PurchaseOrder", "PurchaseOrder")
+                        .WithMany()
+                        .HasForeignKey("FK_PurchaseOrderId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("PurchaseOrder");
+                });
+
+            modelBuilder.Entity("Distribution.Models.PurchaseReturnItem", b =>
+                {
+                    b.HasOne("Distribution.Models.Item", "Item")
+                        .WithMany()
+                        .HasForeignKey("FK_ItemId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.HasOne("Distribution.Models.PurchaseReturn", "PurchaseReturn")
+                        .WithMany("Items")
+                        .HasForeignKey("FK_PurchaseReturnId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("Item");
+
+                    b.Navigation("PurchaseReturn");
+                });
+
             modelBuilder.Entity("Distribution.Models.RideCancelRequest", b =>
                 {
                     b.HasOne("Distribution.Models.DeliveryRun", "Ride")
@@ -1724,6 +2017,11 @@ namespace Distribution.Migrations
                     b.Navigation("Vehicle");
                 });
 
+            modelBuilder.Entity("Distribution.Models.GoodsReceipt", b =>
+                {
+                    b.Navigation("Items");
+                });
+
             modelBuilder.Entity("Distribution.Models.Item", b =>
                 {
                     b.Navigation("Conversions");
@@ -1739,6 +2037,16 @@ namespace Distribution.Migrations
                     b.Navigation("Items");
                 });
 
+            modelBuilder.Entity("Distribution.Models.PurchaseOrder", b =>
+                {
+                    b.Navigation("Items");
+                });
+
+            modelBuilder.Entity("Distribution.Models.PurchaseReturn", b =>
+                {
+                    b.Navigation("Items");
+                });
+
             modelBuilder.Entity("Distribution.Models.Scheme", b =>
                 {
                     b.Navigation("BundleComponents");

Distribution/Models/Enums.cs

@@ -19,7 +19,9 @@ namespace Distribution.Models
         Transfer,
         Damage,
         Adjustment,
-        Load
+        Load,
+        PurchaseReceipt,
+        PurchaseReturn
     }
 
     public enum LoadingSheetStatus
@@ -38,4 +40,6 @@ namespace Distribution.Models
     public enum CancelRequestType { VehicleBreakdown, DriverUnavailable, RouteIssue, Other }
 
     public enum CancelRequestStatus { Pending, Approved, Rejected }
+
+    public enum PurchaseOrderStatus { Issued, PartiallyReceived, Received, Closed, Cancelled }
 }

Distribution/Models/GoodsReceipt.cs

@@ -0,0 +1,26 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class GoodsReceipt : Template
+    {
+        public Guid FK_PurchaseOrderId { get; set; }
+        [ForeignKey("FK_PurchaseOrderId")]
+        public PurchaseOrder PurchaseOrder { get; set; }
+
+        public Guid FK_ReceivedByUserId { get; set; }
+
+        /// <summary>
+        /// Warehouse the accepted quantities are received into. Not listed as a field in
+        /// docs/15_procurement.md's GoodsReceipt table, but required to write StockBalance/
+        /// StockMovement rows (both keyed by LocationId+LocationType) for the accepted quantities.
+        /// </summary>
+        public Guid FK_WarehouseId { get; set; }
+        [ForeignKey("FK_WarehouseId")]
+        public Warehouse Warehouse { get; set; }
+
+        public DateTime ReceivedAt { get; set; } = DateTime.Now;
+
+        public ICollection<GoodsReceiptItem> Items { get; set; } = [];
+    }
+}

Distribution/Models/GoodsReceiptItem.cs

@@ -0,0 +1,21 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class GoodsReceiptItem : Template
+    {
+        public Guid FK_GoodsReceiptId { get; set; }
+        [ForeignKey("FK_GoodsReceiptId")]
+        public GoodsReceipt GoodsReceipt { get; set; }
+
+        public Guid FK_PurchaseOrderItemId { get; set; }
+        [ForeignKey("FK_PurchaseOrderItemId")]
+        public PurchaseOrderItem PurchaseOrderItem { get; set; }
+
+        /// <summary>Added to warehouse stock.</summary>
+        public int AcceptedQuantity { get; set; }
+
+        /// <summary>Damaged/short at receipt, not added to stock.</summary>
+        public int RejectedQuantity { get; set; } = 0;
+    }
+}

Distribution/Models/PurchaseOrder.cs

@@ -0,0 +1,19 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class PurchaseOrder : Template
+    {
+        public Guid FK_SupplierId { get; set; }
+        [ForeignKey("FK_SupplierId")]
+        public Supplier Supplier { get; set; }
+
+        public Guid FK_CreatedByUserId { get; set; }
+
+        public PurchaseOrderStatus Status { get; set; } = PurchaseOrderStatus.Issued;
+
+        public string? CancelReason { get; set; }
+
+        public ICollection<PurchaseOrderItem> Items { get; set; } = [];
+    }
+}

Distribution/Models/PurchaseOrderItem.cs

@@ -0,0 +1,32 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class PurchaseOrderItem : Template
+    {
+        public Guid FK_PurchaseOrderId { get; set; }
+        [ForeignKey("FK_PurchaseOrderId")]
+        public PurchaseOrder PurchaseOrder { get; set; }
+
+        public Guid FK_ItemId { get; set; }
+        [ForeignKey("FK_ItemId")]
+        public Item Item { get; set; }
+
+        public int Quantity { get; set; }
+
+        /// <summary>Agreed cost per unit at the time the PO was issued.</summary>
+        public decimal UnitCost { get; set; }
+
+        /// <summary>Running total, incremented by createGoodsReceipt; drives PurchaseOrder.Status.</summary>
+        public int ReceivedQuantity { get; set; } = 0;
+
+        /// <summary>
+        /// Set by cancelPurchaseOrderLine. Outstanding qty for receiving purposes is
+        /// Quantity - ReceivedQuantity - CancelledQuantity.
+        /// </summary>
+        public int CancelledQuantity { get; set; } = 0;
+
+        /// <summary>True once this line is individually cancelled.</summary>
+        public bool IsCancelled { get; set; } = false;
+    }
+}

Distribution/Models/PurchaseReturn.cs

@@ -0,0 +1,15 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class PurchaseReturn : Template
+    {
+        public Guid FK_PurchaseOrderId { get; set; }
+        [ForeignKey("FK_PurchaseOrderId")]
+        public PurchaseOrder PurchaseOrder { get; set; }
+
+        public string Reason { get; set; }
+
+        public ICollection<PurchaseReturnItem> Items { get; set; } = [];
+    }
+}

Distribution/Models/PurchaseReturnItem.cs

@@ -0,0 +1,18 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class PurchaseReturnItem : Template
+    {
+        public Guid FK_PurchaseReturnId { get; set; }
+        [ForeignKey("FK_PurchaseReturnId")]
+        public PurchaseReturn PurchaseReturn { get; set; }
+
+        public Guid FK_ItemId { get; set; }
+        [ForeignKey("FK_ItemId")]
+        public Item Item { get; set; }
+
+        /// <summary>Returned quantity, decremented from warehouse stock.</summary>
+        public int Quantity { get; set; }
+    }
+}

Distribution/Program.cs

@@ -5,9 +5,12 @@ using Distribution.Features.Brand;
 using Distribution.Features.Category;
 using Distribution.Features.DriverComplianceConfig;
 using Distribution.Features.DriverProfile;
+using Distribution.Features.Grn;
 using Distribution.Features.Item;
 using Distribution.Features.Order;
 using Distribution.Features.PriceList;
+using Distribution.Features.Po;
+using Distribution.Features.PurchaseReturn;
 using Distribution.Features.Region;
 using Distribution.Features.LoadingEvent;
 using Distribution.Features.Ride;
@@ -63,6 +66,9 @@ builder.Services.AddScoped<IStoreKycDocumentRepository, StoreKycDocumentReposito
 builder.Services.AddScoped<IPriceListRepository, PriceListRepository>();
 builder.Services.AddScoped<ISupplierRepository, SupplierRepository>();
 builder.Services.AddScoped<ISchemeRepository, SchemeRepository>();
+builder.Services.AddScoped<IPoRepository, PoRepository>();
+builder.Services.AddScoped<IGrnRepository, GrnRepository>();
+builder.Services.AddScoped<IPurchaseReturnRepository, PurchaseReturnRepository>();
 
 builder.Services.AddScoped<RegionService>();
 builder.Services.AddScoped<RouteService>();
@@ -87,6 +93,9 @@ builder.Services.AddScoped<DriverComplianceConfigService>();
 builder.Services.AddScoped<RideService>();
 builder.Services.AddScoped<LoadingSheetService>();
 builder.Services.AddScoped<SchemeService>();
+builder.Services.AddScoped<PoService>();
+builder.Services.AddScoped<GrnService>();
+builder.Services.AddScoped<PurchaseReturnService>();
 
 builder.Services.AddHttpContextAccessor();
 builder.Services.AddScoped<ICurrentUserService, CurrentUserService>();

Distribution/docs/15_procurement.md

@@ -1,74 +1,413 @@
 # 15 — Procurement / Purchasing
 
-**Status**: Not Started
-**Depends On**: 01 — Item Catalog, 14 — Pricing & Supplier Master Data
+**Status**: Done — migration applied to the database
+**Depends On**: 01 — Item Catalog (Done), 14 — Pricing & Supplier Master Data (Done)
 
 ---
 
 ## Goal
 
-Covers [mainPlan.md §9](./mainPlan.md#9-procurement--purchasing) in full
-— an entirely new subsystem, nothing in this area exists in the current schema.
+Covers [mainPlan.md §9](./mainPlan.md#9-procurement--purchasing) — inbound stock from suppliers,
+the mirror of Order Management's outbound flow to stores. Purchase Requisition is deliberately
+**not** part of this scope (see Background/Context) — `createPurchaseOrder` is the entry point.
 
 ---
 
 ## Background / Context
 
 Inbound stock (`createGoodsReceipt` in [04_loading_event.md](./04_loading_event.md)/
-[mainPlan.md §6](./mainPlan.md#6-warehouse-management)) currently has no
-purchase order to receive against — this step is what creates that PO in the first place.
+[mainPlan.md §6](./mainPlan.md#6-warehouse-management)) had no purchase order to receive against —
+this step creates that PO in the first place.
+
+Sales reps take orders **from** shops (existing `Features/Order`, outbound — decreases stock,
+references `Store`, prices via `PriceListItem.Price`); procurement is the mirror — bringing stock
+**in** from suppliers (`Features/PurchaseOrder`, inbound — increases stock, references `Supplier`,
+costs via `PurchaseOrderItem.UnitCost`). Same header+line-item shape, opposite direction and
+counterparty, which is why they're separate features rather than one generic "Order" entity.
+
+### No requisition step — how "raise a request to purchase" is actually handled
+
+[mainPlan.md §9](./mainPlan.md#9-procurement--purchasing) originally listed
+`createPurchaseRequisition(items[], requestedBy)` as a candidate function. **Dropped from this
+app's design** — the request and the decision to buy collapse into one step:
+
+- Whoever notices stock is low (owner, manager, or eventually an automated low-stock notice) calls
+  `createPurchaseOrder(supplierId, items[])` directly. Issuing the PO **is** the request; it needs
+  no separate approval because only an already-authenticated user can call it (see Permissions —
+  enforcement itself is deferred, matching Supplier/PriceList).
+- There is no Draft → Submitted → Approved chain because restocking authority isn't delegated down
+  to sales reps the way order-taking is.
+- A lower-level "we're low on X" signal is `sendLowStockAlert` (§15 Notifications & Alerts, not yet
+  built) — a notification, not a requisition with its own approval workflow.
+
+### Connections to existing modules
+
+- **Item Catalog** ([01_item_catalog.md](./01_item_catalog.md)): `PurchaseOrderItem.FK_ItemId`,
+  `GoodsReceiptItem` (via `PurchaseOrderItemId` → `PurchaseOrderItem.FK_ItemId`), and
+  `PurchaseReturnItem.FK_ItemId` all reference the same `Item` table sales orders use — one
+  catalog, two directions of stock movement.
+- **Stock Ledger** ([02_stock_ledger.md](./02_stock_ledger.md)): procurement writes to the same
+  `StockBalance`/`StockMovement` tables as the rest of the system rather than a separate stock
+  field — `createGoodsReceipt` credits `StockBalance` (`MovementType.PurchaseReceipt`),
+  `createPurchaseReturn` debits it (`MovementType.PurchaseReturn`). No new stock model was needed.
+- **Pricing** ([14_pricing_and_suppliers.md](./14_pricing_and_suppliers.md)): `PriceListItem.Price`
+  (what you charge a shop) and `PurchaseOrderItem.UnitCost` (what you pay a supplier) are
+  deliberately separate, unlinked fields — procurement never reads or writes `PriceList` rows.
+  Cost-vs-sale margin reporting is left for a later reporting step (see Open Questions).
+- **Supplier Master Data** ([14_pricing_and_suppliers.md](./14_pricing_and_suppliers.md)):
+  `PurchaseOrder.FK_SupplierId` links every PO to one supplier. `SupplierService.EvaluateAsync`
+  (`evaluateSupplier`) is now the only writer of `Supplier.PerformanceScore`, and
+  `SupplierService.DeleteAsync` now blocks soft-delete if any active `PurchaseOrder` references the
+  supplier — both were previously open items in 14's doc, now closed by this step.
+- **Order Management** ([mainPlan.md §1](./mainPlan.md#1-order-management)): while implementing
+  this step, `OrderService.CreateAsync` was found to have no `checkStockAvailability` check at all
+  (mainPlan's own documented gap) — fixed alongside this step: it now rejects an order if requested
+  quantity exceeds total on-hand `StockBalance` for the item, summed across all locations. It still
+  does not decrement stock at order time — that stays deferred to loading/delivery (§04-06), per the
+  existing architecture, to avoid double-decrementing once those steps are built.
 
 ---
 
 ## Data Model Changes
 
-### Purchase Requisition
+Six new tables — three header/line-item pairs (mirrors the `PriceList`/`PriceListItem` split).
 
-`RequestedByUserId`, `Status` (`Draft`, `Submitted`, `Approved`, `Rejected`), line items
-(`ItemId`, `Quantity`).
+### PurchaseOrder
+```
+PurchaseOrder
+├── Id (Guid)                  — PK, from Template
+├── FK_SupplierId (Guid)       — required
+├── FK_CreatedByUserId (Guid)  — required, the user who issued the PO
+├── Status (enum)              — Issued, PartiallyReceived, Received, Closed, Cancelled
+├── CancelReason (string?)     — set by cancelPurchaseOrder
+├── IsActive, CreatedAt        — from Template
+```
 
-### Purchase Order
+### PurchaseOrderItem
+```
+PurchaseOrderItem
+├── Id (Guid)                  — PK, from Template
+├── FK_PurchaseOrderId (Guid)  — required
+├── FK_ItemId (Guid)           — required
+├── Quantity (int)             — ordered quantity
+├── UnitCost (decimal)         — agreed cost per unit at the time the PO was issued
+├── ReceivedQuantity (int)     — running total, incremented by createGoodsReceipt; drives PO Status
+├── CancelledQuantity (int)    — set by cancelPurchaseOrderLine, default 0; outstanding qty for
+│                                 receiving = Quantity - ReceivedQuantity - CancelledQuantity
+├── IsCancelled (bool)         — true once this line is individually cancelled, default false
+```
 
-`SupplierId`, `RequisitionId` (nullable — a PO can be raised without a prior requisition), `Status`
-(`Issued`, `PartiallyReceived`, `Received`, `Closed`), line items (`ItemId`, `Quantity`, `UnitCost`).
+### GoodsReceipt
+```
+GoodsReceipt
+├── Id (Guid)                  — PK, from Template
+├── FK_PurchaseOrderId (Guid)  — required
+├── FK_ReceivedByUserId (Guid) — required
+├── FK_WarehouseId (Guid)      — required; the warehouse the accepted quantities are received into.
+│                                 Not anticipated in the original design — added because
+│                                 StockBalance/StockMovement are keyed by (LocationId, LocationType),
+│                                 so a receiving location is mandatory to credit stock at all.
+├── ReceivedAt (DateTime)
+├── IsActive, CreatedAt        — from Template
+```
 
-### Purchase Return
+### GoodsReceiptItem
+```
+GoodsReceiptItem
+├── Id (Guid)                       — PK, from Template
+├── FK_GoodsReceiptId (Guid)        — required
+├── FK_PurchaseOrderItemId (Guid)   — required, ties the receipt line back to its ordered line
+├── AcceptedQuantity (int)          — added to warehouse stock
+├── RejectedQuantity (int)          — damaged/short at receipt, default 0, not added to stock
+```
 
-`PurchaseOrderId`, reason, line items — goods sent back to the supplier post-receipt.
+### PurchaseReturn
+```
+PurchaseReturn
+├── Id (Guid)                  — PK, from Template
+├── FK_PurchaseOrderId (Guid)  — required
+├── Reason (string)
+├── IsActive, CreatedAt        — from Template
+```
+
+### PurchaseReturnItem
+```
+PurchaseReturnItem
+├── Id (Guid)                    — PK, from Template
+├── FK_PurchaseReturnId (Guid)   — required
+├── FK_ItemId (Guid)             — required
+├── Quantity (int)               — returned quantity, decremented from warehouse stock
+```
+Stock is decremented at the warehouse of the PO's most recent `GoodsReceipt` (the current model
+gives one receiving warehouse per PO in practice; see Open Questions for the multi-warehouse case).
+
+---
+
+## Migrations
+
+One migration, applied:
+1. **AddProcurement** (`20260824110925_AddProcurement`) — created `PurchaseOrders`,
+   `PurchaseOrderItems`, `GoodsReceipts`, `GoodsReceiptItems`, `PurchaseReturns`,
+   `PurchaseReturnItems`, with FKs to `Suppliers`/`Items`/`Warehouses` and indexes on every FK
+   column. Applied via `dotnet ef database update`.
 
 ---
 
 ## API Endpoints
 
-| Function reference | Endpoint intent |
+> No permission policy is enforced on any route below — matches the Supplier/PriceList convention
+> from step 14 (bare `[Authorize]`, authentication required, no per-action policy). See
+> Permissions to Add to Seed.
+
+### Purchase Orders (`Features/PurchaseOrder`)
+| Function reference | Endpoint |
 |---|---|
-| `createPurchaseRequisition(items[], requestedBy)` | `POST /api/purchase-requisitions` |
 | `createPurchaseOrder(supplierId, items[])` | `POST /api/purchase-orders` |
-| `matchInvoiceToPO(invoiceId, poId, grnId)` | `POST /api/purchase-orders/{id}/match-invoice` |
-| `evaluateSupplier(supplierId, criteria)` | `POST /api/suppliers/{id}/evaluate` |
+| `getPurchaseOrder(poId)` | `GET /api/purchase-orders/{id}` |
+| `listPurchaseOrders(filters)` | `GET /api/purchase-orders` |
+| `updatePurchaseOrder(poId, items[])` | `PUT /api/purchase-orders/{id}` |
+| `closePurchaseOrder(poId)` | `POST /api/purchase-orders/{id}/close` |
+| `cancelPurchaseOrder(poId, reason)` | `POST /api/purchase-orders/{id}/cancel` |
+| `cancelPurchaseOrderLine(poId, poItemId, reason)` | `POST /api/purchase-orders/{id}/items/{itemId}/cancel` |
+| `matchInvoiceToPO(poId, invoiceId?, grnId?)` | `POST /api/purchase-orders/{id}/match-invoice` |
+| `resolveInvoiceVariance(poId, variance, resolution)` | `POST /api/purchase-orders/{id}/resolve-variance` |
+
+### Goods Receipt (`Features/Grn`)
+| Function reference | Endpoint |
+|---|---|
+| `createGoodsReceipt(poId, warehouseId, items[])` | `POST /api/purchase-orders/{id}/goods-receipts` |
+| `getGoodsReceipt(grnId)` | `GET /api/goods-receipts/{id}` |
+| `listGoodsReceipts(poId)` | `GET /api/purchase-orders/{id}/goods-receipts` |
+
+### Purchase Returns (`Features/PurchaseReturn`)
+| Function reference | Endpoint |
+|---|---|
 | `createPurchaseReturn(poId, items[], reason)` | `POST /api/purchase-orders/{id}/returns` |
+| `getPurchaseReturn(returnId)` | `GET /api/purchase-returns/{id}` |
+| `listPurchaseReturns(poId)` | `GET /api/purchase-orders/{id}/returns` |
+
+### Supplier Evaluation (`Features/Supplier`, extended)
+| Function reference | Endpoint |
+|---|---|
+| `evaluateSupplier(supplierId)` | `POST /api/suppliers/{id}/evaluate` |
+
+---
+
+## Request / Response Shapes
+
+### POST `/api/purchase-orders`
+```json
+{ "supplierId": "...", "items": [{ "itemId": "...", "quantity": 100, "unitCost": 45.50 }] }
+```
+
+### POST `/api/purchase-orders/{id}/goods-receipts`
+```json
+{ "warehouseId": "...", "items": [
+    { "purchaseOrderItemId": "...", "acceptedQuantity": 95, "rejectedQuantity": 5 }
+] }
+```
+`rejectedQuantity` defaults to 0 if omitted; only `acceptedQuantity` is credited to
+`StockBalance`.
+
+### POST `/api/purchase-orders/{id}/returns`
+```json
+{ "reason": "Damaged in transit", "items": [{ "itemId": "...", "quantity": 10 }] }
+```
+
+### POST `/api/purchase-orders/{id}/resolve-variance`
+```json
+{ "variance": "Quantity mismatch: PO 100, GRN 95", "resolution": "Accepted — short shipment",
+  "adjustedUnitCost": null, "purchaseOrderItemId": "..." }
+```
 
 ---
 
 ## Business Rules
 
-- `createGoodsReceipt` (§6, [04_loading_event.md](./04_loading_event.md)'s warehouse-inbound
-  counterpart) must reference an `Issued`/`PartiallyReceived` Purchase Order — no receipts against
-  a closed or nonexistent PO.
-- `matchInvoiceToPO` (3-way match) must block payment posting in
-  [19_finance_accounting.md](./19_finance_accounting.md) until PO, GRN, and invoice quantities/
-  amounts reconcile within a configurable tolerance.
+1. `createPurchaseOrder` is the entry point to procurement — no prior approval step. A PO starts
+   in `Issued`.
+2. `createGoodsReceipt` must reference an `Issued`/`PartiallyReceived` PurchaseOrder — no receipts
+   against a `Closed`/`Cancelled`/nonexistent PO. Each receipt increments
+   `PurchaseOrderItem.ReceivedQuantity` by `AcceptedQuantity`, credits `StockBalance` at the
+   supplied `warehouseId` (+ a `StockMovement` row, `Type = PurchaseReceipt`), and transitions the
+   PO to `PartiallyReceived` or `Received` (every non-cancelled line's `ReceivedQuantity ==
+   Quantity`).
+3. `closePurchaseOrder` is only valid once a PO is `Received` (or manually closed early with
+   outstanding quantity written off); `cancelPurchaseOrder` is only valid before any goods receipt
+   exists against the PO.
+4. `cancelPurchaseOrderLine` cancels a single `PurchaseOrderItem` (`IsCancelled = true`,
+   `CancelledQuantity = Quantity - ReceivedQuantity`) instead of the whole PO. Only valid while
+   `ReceivedQuantity < Quantity` and the line isn't already fully received or cancelled. The PO
+   auto-completes to `Received` once every non-cancelled line is fully received.
+5. `updatePurchaseOrder` may only change unreceived lines (`ReceivedQuantity == 0`) and only while
+   the PO is `Issued` — a line that has already received stock, or a PO past `Issued`, cannot be
+   edited (use `cancelPurchaseOrderLine`/`createPurchaseReturn` instead).
+6. `createPurchaseReturn` requires at least one prior `createGoodsReceipt` against the PO; return
+   quantity per item cannot exceed `receivedTotal - alreadyReturned` for that item. Debits
+   `StockBalance` at the PO's (most recent) receiving warehouse (+ `StockMovement`,
+   `Type = PurchaseReturn`).
+7. `matchInvoiceToPO` performs PO-vs-GRN quantity/cost reconciliation only — no `Invoice` entity
+   exists yet (step 19 Finance, not built), so `invoiceId` is accepted but not compared against
+   anything. Full 3-way match activates once Finance's `Invoice` model exists. Until then it
+   compares `PurchaseOrderItem.Quantity`/`UnitCost` against `GoodsReceiptItem.AcceptedQuantity` per
+   line and returns a match/variance result — it never blocks or adjusts anything itself.
+8. `resolveInvoiceVariance` is the explicit function that records a variance and its resolution
+   (accept it, request a corrected invoice, or adjust `PurchaseOrderItem.UnitCost` retroactively) —
+   `matchInvoiceToPO` only detects, this function is what acts on a mismatch.
+9. `evaluateSupplier` is the only function permitted to write `Supplier.PerformanceScore`
+   ([14_pricing_and_suppliers.md](./14_pricing_and_suppliers.md) rule 4) — implemented in
+   `SupplierService.EvaluateAsync`, scored from that supplier's PO/GRN history (accepted vs
+   rejected quantity ratio, cancelled vs fulfilled line ratio).
+10. `SupplierService.DeleteAsync` blocks (soft-)deleting a `Supplier` if any active `PurchaseOrder`
+    references it — implemented, closing the previously-open item from
+    [14_pricing_and_suppliers.md](./14_pricing_and_suppliers.md).
+11. `OrderService.CreateAsync` (`checkStockAvailability`, mainPlan §1) now rejects an order if any
+    line's requested quantity exceeds total `StockBalance` for that item summed across every
+    location — added alongside this step since it was a documented gap. Does not reserve or
+    decrement stock; actual decrement stays deferred to loading/delivery (§04-06).
+
+---
+
+## Permissions to Add to Seed
+
+**Status: Not implemented, matching Supplier/PriceList (step 14).** All procurement controllers use
+bare `[Authorize]` (authentication only, no per-action policy) — deliberately kept consistent with
+how Supplier and PriceList currently ship rather than introducing enforcement piecemeal. Target
+permission codes for when policy enforcement is turned on across steps 14/15 together:
+```
+procurement.view, procurement.create, procurement.update, procurement.receive, procurement.return,
+suppliers.evaluate
+```
+No role assignments seeded yet — would mirror the pricing/supplier tier (AreaManager (30) and
+above) per 14's existing target design.
 
 ---
 
 ## Open Questions
 
-- Is procurement in scope for this project at all right now, or is inbound stock assumed to be
-  seeded/manual for the foreseeable future? Confirm before investing in this step — it's the
-  largest net-new subsystem in the reference doc.
+- Where should cost-vs-sale-price margin reporting (`PurchaseOrderItem.UnitCost` vs
+  `PriceListItem.Price`/`Item.SalePrice`) live — a read-only endpoint/report in this step, or a
+  later analytics/reporting step? Not a blocker for the core PO→GRN flow.
+- Landed cost (freight, duty, taxes allocated onto received stock) is out of scope —
+  `PurchaseOrderItem.UnitCost` is the only cost basis captured. Defer unless accurate per-unit cost
+  is needed sooner.
+- Reorder triggers (`setReorderPoint`/`sendLowStockAlert`) are not wired to procurement — restocking
+  stays fully manual until Notifications & Alerts exists.
+- `createPurchaseReturn` assumes a single receiving warehouse per PO (uses the most recent
+  `GoodsReceipt.FK_WarehouseId`). If a PO is ever received across multiple warehouses, the return
+  needs a `warehouseId` on the request instead of inferring one — not needed yet since nothing
+  splits a receipt across warehouses today.
+- Permission policy enforcement (`procurement.*`) is deferred — see Permissions to Add to Seed.
 
 ---
 
 ## Implementation Notes
 
-> Fill this section in during planning discussion before writing any code.
+### File structure (as built)
+```
+Features/
+  PurchaseOrder/
+    PoController.cs        — /api/purchase-orders (create/get/list/update/close/cancel/
+                              cancel-line/match-invoice/resolve-variance)
+    PoDTOs.cs               — CreatePoRequest, UpdatePoRequest(+Line), CancelPoRequest(+Line),
+                              PoResponse(+Item), InvoiceMatchResult(+Line), ResolveInvoiceVarianceRequest
+    PoService.cs            — createPurchaseOrder, updatePurchaseOrder, closePurchaseOrder,
+                              cancelPurchaseOrder, cancelPurchaseOrderLine, matchInvoiceToPO,
+                              resolveInvoiceVariance
+    IPoRepository.cs / PoRepository.cs
+  Grn/
+    GrnController.cs        — nested under /api/purchase-orders/{id}/goods-receipts,
+                              /api/goods-receipts/{id}
+    GrnDTOs.cs               — CreateGrnRequest, GrnResponse(+Item)
+    GrnService.cs            — createGoodsReceipt (credits StockBalance/StockMovement, updates
+                              PurchaseOrderItem.ReceivedQuantity, transitions PO status)
+    IGrnRepository.cs / GrnRepository.cs
+  PurchaseReturn/
+    PurchaseReturnController.cs   — nested under /api/purchase-orders/{id}/returns,
+                                     /api/purchase-returns/{id}
+    PurchaseReturnDTOs.cs
+    PurchaseReturnService.cs      — createPurchaseReturn (debits StockBalance/StockMovement)
+    IPurchaseReturnRepository.cs / PurchaseReturnRepository.cs
+  Supplier/
+    SupplierController.cs   — extended: POST /{id}/evaluate
+    SupplierService.cs      — extended: EvaluateAsync (only writer of PerformanceScore),
+                              DeleteAsync now blocks if an active PurchaseOrder references the supplier
+  Order/
+    OrderService.cs          — extended: CreateAsync now calls HasSufficientStockAsync
+                              (checkStockAvailability) before resolving price/inserting the order
+
+Models/
+  PurchaseOrder.cs, PurchaseOrderItem.cs   (new)
+  GoodsReceipt.cs, GoodsReceiptItem.cs     (new)
+  PurchaseReturn.cs, PurchaseReturnItem.cs (new)
+  Enums.cs                                 (extended — PurchaseOrderStatus enum added)
+
+Data/AppDBContext.cs
+  DbSets added for all six entities; FK relationships via Fluent API, DeleteBehavior.Restrict
+
+Migrations/
+  20260824110925_AddProcurement   (applied)
+
+Program.cs
+  IPoRepository/PoRepository, IGrnRepository/GrnRepository,
+  IPurchaseReturnRepository/PurchaseReturnRepository registered; PoService, GrnService,
+  PurchaseReturnService registered (Supplier registrations already existed from step 14)
+```
+
+### How the models connect
+```
+Supplier (existing, step 14)
+   ▲
+   │ FK_SupplierId
+PurchaseOrder ──► GoodsReceipt ──► StockBalance/StockMovement (Stock Ledger, §02)
+   │                  │               (credited: AcceptedQuantity, MovementType.PurchaseReceipt)
+   │                  └─ GoodsReceiptItem ─► PurchaseOrderItem
+   │                     (AcceptedQuantity increments stock; also increments
+   │                      PurchaseOrderItem.ReceivedQuantity, which drives PurchaseOrder.Status)
+   │
+   ├─ PurchaseOrderItem (FK_ItemId, Quantity, UnitCost, ReceivedQuantity, CancelledQuantity)
+   │
+   └─ PurchaseReturn ──► PurchaseReturnItem ──► StockBalance/StockMovement
+      (FK_PurchaseOrderId)  (FK_ItemId, Quantity;    (debited: MovementType.PurchaseReturn,
+                              via the PO's receiving   at the PO's receiving warehouse)
+                              warehouse)
+
+Invoice (Finance, step 19 — not yet built)
+   └─ matchInvoiceToPO reconciles PurchaseOrderItem vs GoodsReceiptItem only, today (invoiceId
+      accepted but unused); full 3-way match activates once Invoice exists.
+
+evaluateSupplier reads that supplier's PurchaseOrders/GoodsReceipts (accepted-vs-rejected quantity,
+cancelled-vs-fulfilled line ratio) and writes Supplier.PerformanceScore — no other function may
+write it.
+```
+
+### Goods receipt flow (as implemented)
+```
+GrnService.CreateAsync(purchaseOrderId, request, receivedByUserId):
+  po = load PurchaseOrder with Items, must be Issued or PartiallyReceived else throw
+  for each (purchaseOrderItemId, acceptedQty, rejectedQty) in request.Items:
+    poItem = po.Items.Single(purchaseOrderItemId)
+    outstanding = poItem.Quantity - poItem.ReceivedQuantity - poItem.CancelledQuantity
+    guard acceptedQty + rejectedQty <= outstanding else throw
+    poItem.ReceivedQuantity += acceptedQty
+    credit StockBalance(itemId, request.WarehouseId, Warehouse) += acceptedQty
+    add StockMovement(Type = PurchaseReceipt, ToLocation = warehouse, ReferenceId = goodsReceipt.Id)
+  po.Status = every non-cancelled poItem.ReceivedQuantity == poItem.Quantity
+              ? Received : PartiallyReceived
+  commit GoodsReceipt + GoodsReceiptItems + updated PurchaseOrderItem rows + StockBalance/Movement
+  in one transaction (IUnitOfWork.Begin/Commit)
+```
+
+### Purchase return flow (as implemented)
+```
+PurchaseReturnService.CreateAsync(purchaseOrderId, request, createdByUserId):
+  po = load PurchaseOrder, must have >= 1 GoodsReceipt else throw
+  warehouseId = most recent GoodsReceipt.FK_WarehouseId for this Po
+  for each (itemId, qty) in request.Items:
+    received = sum(GoodsReceiptItem.AcceptedQuantity for itemId across po's receipts)
+    alreadyReturned = sum(PurchaseReturnItem.Quantity for itemId across po's prior returns)
+    guard qty <= received - alreadyReturned else throw
+    debit StockBalance(itemId, warehouseId) -= qty
+    add StockMovement(Type = PurchaseReturn, FromLocation = warehouseId, ReferenceId = purchaseReturn.Id)
+  commit PurchaseReturn + PurchaseReturnItems + StockBalance/Movement in one transaction
+```

Distribution/docs/mainPlan.md

@@ -16,6 +16,7 @@
 | Soft Deletes | Done | IsActive pattern on all entities |
 | Price Lists / Suppliers | Done | Region-scoped price lists + supplier master; see [14_pricing_and_suppliers.md](./14_pricing_and_suppliers.md) |
 | Promotions & Trade Schemes | Done | BuyXGetY/FreeBundle/SlabDiscount/FlatPercent schemes, free-goods fulfillment, spend/ROI tracking; see [17_promotions_schemes.md](./17_promotions_schemes.md) |
+| Procurement / Purchasing | Done | Purchase Order → Goods Receipt → Purchase Return, supplier evaluation; see [15_procurement.md](./15_procurement.md) |
 
 ## Known Gaps in Existing System (Pre-Work)
 
@@ -52,7 +53,7 @@ They must be resolved before new feature steps begin because later steps depend
 | 12 | Store Management (Beyond CRUD) | Done | 00 | [12_store_management.md](./12_store_management.md) |
 | 13 | Fleet Management (Beyond CRUD) | Not Started | 00 | [13_fleet_management.md](./13_fleet_management.md) |
 | 14 | Pricing & Supplier Master Data | Done | 01 | [14_pricing_and_suppliers.md](./14_pricing_and_suppliers.md) |
-| 15 | Procurement / Purchasing | Not Started | 01, 14 | [15_procurement.md](./15_procurement.md) |
+| 15 | Procurement / Purchasing | Done | 01, 14 | [15_procurement.md](./15_procurement.md) |
 | 16 | Sales Force Automation / CRM | Not Started | 12 | [16_sfa_crm.md](./16_sfa_crm.md) |
 | 17 | Promotions & Trade Scheme Management | Done | 01, 14 | [17_promotions_schemes.md](./17_promotions_schemes.md) |
 | 18 | Returns & Claims Management | Not Started | 05, 06 | [18_returns_claims.md](./18_returns_claims.md) |
@@ -82,9 +83,9 @@ here — see `SRS_User_Management_Module.pdf`.
 
 | Function | What it does | Status |
 |---|---|---|
-| `createOrder(storeId, items[], salesRepId)` | Validates stock/credit, creates a new order in `pending` state. | Partially implemented - `OrderService.CreateAsync` exists, enforces store scope, blocks inactive stores, and applies the unverified-KYC order threshold from config. It still has no stock validation, credit-limit validation, approval flow, or order state machine. |
+| `createOrder(storeId, items[], salesRepId)` | Validates stock/credit, creates a new order in `pending` state. | Partially implemented - `OrderService.CreateAsync` exists, enforces store scope, blocks inactive stores, applies the unverified-KYC order threshold from config, and now checks stock availability (see `checkStockAvailability` below). It still has no credit-limit validation, approval flow, or order state machine. |
 | `validateCreditLimit(storeId, orderAmount)` | Checks store's outstanding balance + new order value against its credit limit. | Not implemented - `Store` now has `CreditLimit` and `OutstandingBalance`, but there is no dedicated validator or order-time credit-limit enforcement yet. |
-| `checkStockAvailability(items[])` | Confirms requested SKUs/quantities are available at the fulfilling warehouse. | Not implemented — depends on [02_stock_ledger.md](./02_stock_ledger.md). |
+| `checkStockAvailability(items[])` | Confirms requested SKUs/quantities are available at the fulfilling warehouse. | Implemented — `OrderService.CreateAsync` rejects an order if any line's requested quantity exceeds total `StockBalance` for that item summed across every location (added alongside [15_procurement.md](./15_procurement.md)). Not location-specific yet (no fulfilling-warehouse concept on `Store`/`Order`), and does not reserve or decrement stock — that stays deferred to loading/delivery (§05-06). |
 | `applyPricingAndDiscounts(orderId)` | Runs the active price list and eligible scheme rules against order lines. | Partially implemented — `OrderService.CreateAsync` resolves the price-list half via `PriceListService.ResolveUnitPriceAsync` (region-scoped → global → `Item.SalePrice`, or a caller-supplied `UnitPrice`). The scheme-discount half now exists as a separate call — `SchemeService.EvaluateEligibilityAsync`/`ApplySchemeAsync` (§11) — but is not yet auto-invoked from `OrderService.CreateAsync`; the caller applies a scheme explicitly via `POST /api/orders/{id}/apply-scheme` after order creation. |
 | `submitOrderForApproval(orderId)` | Routes the order to the correct approver based on its value/discount threshold. | Not implemented — depends on [08_sales_agent_controls.md](./08_sales_agent_controls.md). |
 | `approveOrder(orderId, approverId)` / `rejectOrder(orderId, reason)` | Moves order to `approved` or `rejected`, logging the actor. | Not implemented. |
@@ -156,7 +157,7 @@ here — see `SRS_User_Management_Module.pdf`.
 
 | Function | What it does | Status |
 |---|---|---|
-| `createGoodsReceipt(poId, receivedItems[])` | Records inbound stock against a purchase order (GRN). | Not implemented — depends on §9 Procurement. |
+| `createGoodsReceipt(poId, receivedItems[])` | Records inbound stock against a purchase order (GRN). | Implemented — `POST /api/purchase-orders/{id}/goods-receipts`, see [15_procurement.md](./15_procurement.md). Credits `StockBalance`/`StockMovement` for accepted quantities and transitions the PO's status. |
 | `inspectGoodsReceipt(grnId, inspectionResult)` | Logs quality-check outcome before putaway. | Not implemented. |
 | `putawayStock(grnId, locationAssignments[])` | Assigns received stock to warehouse locations (zone/ABC-based). | Not implemented — depends on [02_stock_ledger.md](./02_stock_ledger.md). |
 | `getStockByLocation(warehouseId, sku)` | Returns real-time quantity and location for a SKU. | Not implemented — depends on [02_stock_ledger.md](./02_stock_ledger.md). |
@@ -195,10 +196,10 @@ here — see `SRS_User_Management_Module.pdf`.
 | Function | What it does | Status |
 |---|---|---|
 | `createPurchaseRequisition(items[], requestedBy)` | Raises an internal request to purchase stock. | Not implemented — no procurement entities exist. |
-| `createPurchaseOrder(supplierId, items[])` | Issues a PO to a supplier. | Not implemented. |
-| `matchInvoiceToPO(invoiceId, poId, grnId)` | Performs the 3-way match (PO–GRN–Invoice) before payment. | Not implemented. |
-| `evaluateSupplier(supplierId, criteria)` | Scores a supplier on delivery/quality/price performance. | Not implemented. |
-| `createPurchaseReturn(poId, items[], reason)` | Initiates a return of received goods to the supplier. | Not implemented. |
+| `createPurchaseOrder(supplierId, items[])` | Issues a PO to a supplier. | Implemented — `POST /api/purchase-orders`, see [15_procurement.md](./15_procurement.md). Also has `updatePurchaseOrder`, `closePurchaseOrder`, `cancelPurchaseOrder`, `cancelPurchaseOrderLine`. |
+| `matchInvoiceToPO(invoiceId, poId, grnId)` | Performs the 3-way match (PO–GRN–Invoice) before payment. | Partially implemented — `POST /api/purchase-orders/{id}/match-invoice` reconciles PurchaseOrderItem vs GoodsReceiptItem quantities/cost only; full 3-way match activates once Finance's `Invoice` entity (§13, not built) exists. `resolveInvoiceVariance` records the mismatch and its resolution. |
+| `evaluateSupplier(supplierId, criteria)` | Scores a supplier on delivery/quality/price performance. | Implemented — `POST /api/suppliers/{id}/evaluate`, the only writer of `Supplier.PerformanceScore`. Scored from accepted-vs-rejected quantity ratio and cancelled-vs-fulfilled line ratio across that supplier's PurchaseOrders/GoodsReceipts. |
+| `createPurchaseReturn(poId, items[], reason)` | Initiates a return of received goods to the supplier. | Implemented — `POST /api/purchase-orders/{id}/returns`, see [15_procurement.md](./15_procurement.md). Debits `StockBalance`/`StockMovement` at the PO's receiving warehouse. |
 
 ### 10. Sales Force Automation (SFA) / CRM