completed invetory updates

Backend/ERPCore/Controllers/BrandsController.cs

@@ -0,0 +1,67 @@
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Brands;
+using ERPCore.Dtos.Common;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Brand master endpoints (docs/11-BACKEND-PHASE1.md §2.6).</summary>
+[Route("api/v1/brands")]
+public sealed class BrandsController : ApiControllerBase
+{
+    private readonly IBrandService _brands;
+
+    public BrandsController(IBrandService brands) => _brands = brands;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<BrandDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<BrandDto>>> List(
+        [FromQuery] PageQuery query, [FromQuery] EntityStatus? status, CancellationToken ct)
+        => Ok(await _brands.ListAsync(query, status, ct));
+
+    [HttpGet("{brandId:int}")]
+    [ProducesResponseType(typeof(BrandDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<BrandDto>> GetById(int brandId, CancellationToken ct)
+    {
+        var result = await _brands.GetAsync(brandId, ct);
+        if (result is null) return NotFound();
+
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    [HttpPost]
+    [ProducesResponseType(typeof(BrandDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<BrandDto>> Create([FromBody] CreateBrandRequest request, CancellationToken ct)
+    {
+        var result = await _brands.CreateAsync(request, ct);
+        SetETag(result.RowVersion);
+        return Created($"/api/v1/brands/{result.Value.BrandId}", result.Value);
+    }
+
+    [HttpPut("{brandId:int}")]
+    [ProducesResponseType(typeof(BrandDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status412PreconditionFailed)]
+    public async Task<ActionResult<BrandDto>> Update(int brandId, [FromBody] UpdateBrandRequest request, CancellationToken ct)
+    {
+        var expected = RequireIfMatch();
+        var result = await _brands.UpdateAsync(brandId, request, expected, ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    /// <summary>Deactivate/reactivate. Masters are never hard-deleted (FR-MD-08).</summary>
+    [HttpPatch("{brandId:int}/status")]
+    [ProducesResponseType(StatusCodes.Status204NoContent)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> SetStatus(int brandId, [FromBody] UpdateBrandStatusRequest request, CancellationToken ct)
+    {
+        await _brands.SetStatusAsync(brandId, request.Status, ct);
+        return NoContent();
+    }
+}

Backend/ERPCore/Controllers/CategoriesController.cs

@@ -1,3 +1,4 @@
+using ERPCore.Domain.Enums;
 using ERPCore.Dtos.Categories;
 using ERPCore.Dtos.Common;
 using ERPCore.Services.Interfaces;
@@ -5,7 +6,11 @@ using Microsoft.AspNetCore.Mvc;
 
 namespace ERPCore.Controllers;
 
-/// <summary>Category endpoints (docs/11-BACKEND-PHASE1.md §2.3).</summary>
+/// <summary>
+/// Category endpoints (docs/11-BACKEND-PHASE1.md §2.3), including the subcategories
+/// nested beneath each category. The hierarchy is exactly two levels deep — the old
+/// <c>?tree=true</c> parameter is gone along with the self-nesting model.
+/// </summary>
 [Route("api/v1/categories")]
 public sealed class CategoriesController : ApiControllerBase
 {
@@ -13,19 +18,79 @@ public sealed class CategoriesController : ApiControllerBase
 
     public CategoriesController(ICategoryService categories) => _categories = categories;
 
-    /// <summary>Flat paged list, or a nested tree when <c>tree=true</c>.</summary>
     [HttpGet]
     [ProducesResponseType(typeof(PagedResponse<CategoryDto>), StatusCodes.Status200OK)]
-    [ProducesResponseType(typeof(IReadOnlyList<CategoryTreeDto>), StatusCodes.Status200OK)]
-    public async Task<IActionResult> List([FromQuery] PageQuery query, [FromQuery] bool tree, CancellationToken ct)
-        => tree ? Ok(await _categories.GetTreeAsync(ct)) : Ok(await _categories.ListAsync(query, ct));
+    public async Task<ActionResult<PagedResponse<CategoryDto>>> List(
+        [FromQuery] PageQuery query, [FromQuery] EntityStatus? status, CancellationToken ct)
+        => Ok(await _categories.ListAsync(query, status, ct));
+
+    [HttpGet("{categoryId:int}")]
+    [ProducesResponseType(typeof(CategoryDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<CategoryDto>> GetById(int categoryId, CancellationToken ct)
+    {
+        var result = await _categories.GetAsync(categoryId, ct);
+        if (result is null) return NotFound();
+
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
 
     [HttpPost]
     [ProducesResponseType(typeof(CategoryDto), StatusCodes.Status201Created)]
-    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
     public async Task<ActionResult<CategoryDto>> Create([FromBody] CreateCategoryRequest request, CancellationToken ct)
     {
-        var dto = await _categories.CreateAsync(request, ct);
-        return Created($"/api/v1/categories/{dto.CategoryId}", dto);
+        var result = await _categories.CreateAsync(request, ct);
+        SetETag(result.RowVersion);
+        return Created($"/api/v1/categories/{result.Value.CategoryId}", result.Value);
+    }
+
+    [HttpPut("{categoryId:int}")]
+    [ProducesResponseType(typeof(CategoryDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status412PreconditionFailed)]
+    public async Task<ActionResult<CategoryDto>> Update(
+        int categoryId, [FromBody] UpdateCategoryRequest request, CancellationToken ct)
+    {
+        var expected = RequireIfMatch();
+        var result = await _categories.UpdateAsync(categoryId, request, expected, ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    /// <summary>Deactivate/reactivate. Masters are never hard-deleted (FR-MD-08).</summary>
+    [HttpPatch("{categoryId:int}/status")]
+    [ProducesResponseType(StatusCodes.Status204NoContent)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> SetStatus(
+        int categoryId, [FromBody] UpdateCategoryStatusRequest request, CancellationToken ct)
+    {
+        await _categories.SetStatusAsync(categoryId, request.Status, ct);
+        return NoContent();
+    }
+
+    // Subcategories — nested under their parent category (docs/11 §2.3).
+    // Updates live on SubCategoriesController at /api/v1/subcategories/{id}.
+
+    [HttpGet("{categoryId:int}/subcategories")]
+    [ProducesResponseType(typeof(PagedResponse<SubCategoryDto>), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<PagedResponse<SubCategoryDto>>> ListSubCategories(
+        int categoryId, [FromQuery] PageQuery query, [FromQuery] EntityStatus? status, CancellationToken ct)
+        => Ok(await _categories.ListSubCategoriesAsync(categoryId, query, status, ct));
+
+    [HttpPost("{categoryId:int}/subcategories")]
+    [ProducesResponseType(typeof(SubCategoryDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<SubCategoryDto>> CreateSubCategory(
+        int categoryId, [FromBody] CreateSubCategoryRequest request, CancellationToken ct)
+    {
+        var result = await _categories.CreateSubCategoryAsync(categoryId, request, ct);
+        SetETag(result.RowVersion);
+        return Created($"/api/v1/subcategories/{result.Value.SubCategoryId}", result.Value);
     }
 }

Backend/ERPCore/Controllers/ItemTypesController.cs

@@ -0,0 +1,73 @@
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.ItemTypes;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>
+/// Item type master endpoints (docs/11-BACKEND-PHASE1.md §2.7) — the Color/Size/Material
+/// dimension names. <c>GET</c> is the reason this master exists: it populates the item
+/// builder's dropdown. Items never reference an item type; the chosen values are encoded
+/// into the client-generated SKU (docs/10 Part C.9).
+/// </summary>
+[Route("api/v1/item-types")]
+public sealed class ItemTypesController : ApiControllerBase
+{
+    private readonly IItemTypeService _itemTypes;
+
+    public ItemTypesController(IItemTypeService itemTypes) => _itemTypes = itemTypes;
+
+    /// <summary>Feeds the frontend item-builder dropdown; filter <c>status=Active</c> for selectable rows.</summary>
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<ItemTypeDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<ItemTypeDto>>> List(
+        [FromQuery] PageQuery query, [FromQuery] EntityStatus? status, CancellationToken ct)
+        => Ok(await _itemTypes.ListAsync(query, status, ct));
+
+    [HttpGet("{itemTypeId:int}")]
+    [ProducesResponseType(typeof(ItemTypeDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<ItemTypeDto>> GetById(int itemTypeId, CancellationToken ct)
+    {
+        var result = await _itemTypes.GetAsync(itemTypeId, ct);
+        if (result is null) return NotFound();
+
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    [HttpPost]
+    [ProducesResponseType(typeof(ItemTypeDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<ItemTypeDto>> Create([FromBody] CreateItemTypeRequest request, CancellationToken ct)
+    {
+        var result = await _itemTypes.CreateAsync(request, ct);
+        SetETag(result.RowVersion);
+        return Created($"/api/v1/item-types/{result.Value.ItemTypeId}", result.Value);
+    }
+
+    [HttpPut("{itemTypeId:int}")]
+    [ProducesResponseType(typeof(ItemTypeDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status412PreconditionFailed)]
+    public async Task<ActionResult<ItemTypeDto>> Update(int itemTypeId, [FromBody] UpdateItemTypeRequest request, CancellationToken ct)
+    {
+        var expected = RequireIfMatch();
+        var result = await _itemTypes.UpdateAsync(itemTypeId, request, expected, ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    /// <summary>Deactivate/reactivate. Masters are never hard-deleted (FR-MD-08).</summary>
+    [HttpPatch("{itemTypeId:int}/status")]
+    [ProducesResponseType(StatusCodes.Status204NoContent)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> SetStatus(int itemTypeId, [FromBody] UpdateItemTypeStatusRequest request, CancellationToken ct)
+    {
+        await _itemTypes.SetStatusAsync(itemTypeId, request.Status, ct);
+        return NoContent();
+    }
+}

Backend/ERPCore/Controllers/ItemsController.cs

@@ -21,9 +21,11 @@ public sealed class ItemsController : ApiControllerBase
         [FromQuery] PageQuery query,
         [FromQuery] EntityStatus? status,
         [FromQuery] int? categoryId,
+        [FromQuery] int? subCategoryId,
+        [FromQuery] int? brandId,
         [FromQuery] TrackingMode? trackingMode,
         CancellationToken ct)
-        => Ok(await _items.ListAsync(query, status, categoryId, trackingMode, ct));
+        => Ok(await _items.ListAsync(query, status, categoryId, subCategoryId, brandId, trackingMode, ct));
 
     /// <summary>Get a single item; returns an <c>ETag</c> for optimistic concurrency.</summary>
     [HttpGet("{itemId:int}")]

Backend/ERPCore/Controllers/ProductConfigController.cs

@@ -0,0 +1,46 @@
+using ERPCore.Dtos.Config;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>
+/// Product configuration endpoints (docs/11-BACKEND-PHASE1.md §2.8) — the singleton
+/// feature gate for subcategories/brands/item-types.
+/// <para>
+/// <b>Authorization:</b> writes are admitted by the inherited ERP door policy only.
+/// A dedicated <c>CONFIG_MANAGE</c> permission is reserved for when per-endpoint RBAC
+/// lands (FR-X-01, currently deferred) — at that point this action gets the attribute
+/// with no other change. Until then any ERP-admitted user can flip these flags; that is
+/// the accepted Phase-1 posture, consistent with every other endpoint.
+/// </para>
+/// </summary>
+[Route("api/v1/product-config")]
+public sealed class ProductConfigController : ApiControllerBase
+{
+    private readonly IProductConfigService _config;
+
+    public ProductConfigController(IProductConfigService config) => _config = config;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(ProductConfigDto), StatusCodes.Status200OK)]
+    public async Task<ActionResult<ProductConfigDto>> Get(CancellationToken ct)
+    {
+        var result = await _config.GetAsync(ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    [HttpPut]
+    [ProducesResponseType(typeof(ProductConfigDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(StatusCodes.Status412PreconditionFailed)]
+    public async Task<ActionResult<ProductConfigDto>> Update(
+        [FromBody] UpdateProductConfigRequest request, CancellationToken ct)
+    {
+        var expected = RequireIfMatch();
+        var result = await _config.UpdateAsync(request, expected, ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+}

Backend/ERPCore/Controllers/SubCategoriesController.cs

@@ -0,0 +1,56 @@
+using ERPCore.Dtos.Categories;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>
+/// Subcategory endpoints addressed by their own id (docs/11-BACKEND-PHASE1.md §2.3).
+/// Listing and creation live under the parent category on <see cref="CategoriesController"/>,
+/// since a subcategory only exists in the context of one.
+/// </summary>
+[Route("api/v1/subcategories")]
+public sealed class SubCategoriesController : ApiControllerBase
+{
+    private readonly ICategoryService _categories;
+
+    public SubCategoriesController(ICategoryService categories) => _categories = categories;
+
+    [HttpGet("{subCategoryId:int}")]
+    [ProducesResponseType(typeof(SubCategoryDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<SubCategoryDto>> GetById(int subCategoryId, CancellationToken ct)
+    {
+        var result = await _categories.GetSubCategoryAsync(subCategoryId, ct);
+        if (result is null) return NotFound();
+
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    /// <summary>Renames a subcategory. It cannot be moved to another category — see the request DTO.</summary>
+    [HttpPut("{subCategoryId:int}")]
+    [ProducesResponseType(typeof(SubCategoryDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status412PreconditionFailed)]
+    public async Task<ActionResult<SubCategoryDto>> Update(
+        int subCategoryId, [FromBody] UpdateSubCategoryRequest request, CancellationToken ct)
+    {
+        var expected = RequireIfMatch();
+        var result = await _categories.UpdateSubCategoryAsync(subCategoryId, request, expected, ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    /// <summary>Deactivate/reactivate. Masters are never hard-deleted (FR-MD-08).</summary>
+    [HttpPatch("{subCategoryId:int}/status")]
+    [ProducesResponseType(StatusCodes.Status204NoContent)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> SetStatus(
+        int subCategoryId, [FromBody] UpdateSubCategoryStatusRequest request, CancellationToken ct)
+    {
+        await _categories.SetSubCategoryStatusAsync(subCategoryId, request.Status, ct);
+        return NoContent();
+    }
+}

Backend/ERPCore/Domain/Entities/Brand.cs

@@ -0,0 +1,21 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Brand master (FR-MD-09). Referenced optionally by <see cref="Item.BrandId"/>.
+/// Mutable aggregate with a <see cref="RowVersion"/> ETag token. Deactivated, not
+/// deleted, when referenced (FR-MD-08). Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// </summary>
+public class Brand
+{
+    public int BrandId { get; set; }
+    public string Name { get; set; } = string.Empty;
+    public EntityStatus Status { get; set; } = EntityStatus.Active;
+
+    public DateTime CreatedAt { get; set; }
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>PostgreSQL xmin-backed optimistic concurrency token (ETag source).</summary>
+    public uint RowVersion { get; set; }
+}

Backend/ERPCore/Domain/Entities/Category.cs

@@ -1,15 +1,25 @@
+using ERPCore.Domain.Enums;
+
 namespace ERPCore.Domain.Entities;
 
 /// <summary>
-/// Hierarchical item category (FR-MD-04). A null <see cref="ParentId"/> denotes a
-/// root category. Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// Item category (FR-MD-04) — the top level of a two-level hierarchy. The optional level
+/// below is <see cref="SubCategory"/>; categories no longer self-nest (the former
+/// <c>parent_id</c> tree was replaced in migration #2).
+/// Mutable aggregate with a <see cref="RowVersion"/> ETag token. Deactivated, not
+/// deleted, when referenced (FR-MD-08). Model: docs/10-BACKEND-PHASE1.md Part C.1.
 /// </summary>
 public class Category
 {
     public int CategoryId { get; set; }
     public string Name { get; set; } = string.Empty;
+    public EntityStatus Status { get; set; } = EntityStatus.Active;
 
-    public int? ParentId { get; set; }
-    public Category? Parent { get; set; }
-    public ICollection<Category> Children { get; set; } = new List<Category>();
+    public DateTime CreatedAt { get; set; }
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>PostgreSQL xmin-backed optimistic concurrency token (ETag source).</summary>
+    public uint RowVersion { get; set; }
+
+    public ICollection<SubCategory> SubCategories { get; set; } = new List<SubCategory>();
 }

Backend/ERPCore/Domain/Entities/Item.cs

@@ -17,13 +17,20 @@ public class Item
     public int CategoryId { get; set; }
     public Category? Category { get; set; }
 
+    /// <summary>Optional second level below <see cref="CategoryId"/>; must belong to it.</summary>
+    public int? SubCategoryId { get; set; }
+    public SubCategory? SubCategory { get; set; }
+
+    public int? BrandId { get; set; }
+    public Brand? Brand { get; set; }
+
     public int BaseUomId { get; set; }
     public Uom? BaseUom { get; set; }
 
     public int? DefaultVendorId { get; set; }
     public Vendor? DefaultVendor { get; set; }
 
-    public ItemType ItemType { get; set; }
+    public StockNature StockNature { get; set; }
     public TrackingMode TrackingMode { get; set; }
     public string? TaxClass { get; set; }
     public EntityStatus Status { get; set; } = EntityStatus.Active;

Backend/ERPCore/Domain/Entities/ItemType.cs

@@ -0,0 +1,31 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Item type master (FR-MD-10) — a selectable dimension name such as Color, Size or
+/// Material.
+/// <para>
+/// <b>Deliberately unlinked.</b> Nothing references this entity and it references
+/// nothing: there is no value table and no join to <see cref="Item"/>. Its only job is
+/// to feed the frontend's item-builder dropdown via <c>GET /item-types</c>. The chosen
+/// values (Red, S, M) are encoded by the client into the generated SKU
+/// (e.g. <c>BL-100-0003</c>) and are never stored or parsed server-side — the item list
+/// is the record of what was built. See the accepted trade-off in docs/10 Part C.9.
+/// </para>
+/// Not to be confused with <see cref="Enums.StockNature"/> (Stocked/NonStocked/Service),
+/// which is what the old <c>ItemType</c> enum became.
+/// Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// </summary>
+public class ItemType
+{
+    public int ItemTypeId { get; set; }
+    public string Name { get; set; } = string.Empty;
+    public EntityStatus Status { get; set; } = EntityStatus.Active;
+
+    public DateTime CreatedAt { get; set; }
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>PostgreSQL xmin-backed optimistic concurrency token (ETag source).</summary>
+    public uint RowVersion { get; set; }
+}

Backend/ERPCore/Domain/Entities/ProductConfig.cs

@@ -0,0 +1,35 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Product configuration (FR-MD-11) — a <b>singleton row</b> (single-tenant, docs/00-CORE §1)
+/// gating optional product master-data features.
+/// <para>
+/// <see cref="SubcategoriesEnabled"/> and <see cref="BrandsEnabled"/> are enforced
+/// server-side: an Item write carrying a subcategory/brand while the flag is off is
+/// rejected with <c>CONFIG_DISABLED</c>. <see cref="ItemTypesEnabled"/> is
+/// <b>advisory only</b> — items carry no item-type reference (see <see cref="ItemType"/>),
+/// so there is nothing on a write to reject; the frontend honours it by hiding the
+/// builder's type section. Reads are never gated, so existing data stays visible after a
+/// flag is switched off.
+/// </para>
+/// Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// </summary>
+public class ProductConfig
+{
+    /// <summary>Always 1 — the singleton row's id.</summary>
+    public const int SingletonId = 1;
+
+    public int ConfigId { get; set; }
+
+    public bool SubcategoriesEnabled { get; set; } = true;
+    public bool BrandsEnabled { get; set; } = true;
+    public bool ItemTypesEnabled { get; set; } = true;
+
+    public DateTime? UpdatedAt { get; set; }
+
+    public int? UpdatedBy { get; set; }
+    public User? UpdatedByUser { get; set; }
+
+    /// <summary>PostgreSQL xmin-backed optimistic concurrency token (ETag source).</summary>
+    public uint RowVersion { get; set; }
+}

Backend/ERPCore/Domain/Entities/SubCategory.cs

@@ -0,0 +1,26 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Subcategory — the single optional level below <see cref="Category"/> (FR-MD-04).
+/// Replaces the former self-referencing CATEGORY.parent_id tree: the hierarchy is
+/// exactly two levels deep and cannot nest further. Referenced optionally by
+/// <see cref="Item.SubCategoryId"/>. Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// </summary>
+public class SubCategory
+{
+    public int SubCategoryId { get; set; }
+    public string Name { get; set; } = string.Empty;
+
+    public int CategoryId { get; set; }
+    public Category? Category { get; set; }
+
+    public EntityStatus Status { get; set; } = EntityStatus.Active;
+
+    public DateTime CreatedAt { get; set; }
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>PostgreSQL xmin-backed optimistic concurrency token (ETag source).</summary>
+    public uint RowVersion { get; set; }
+}

Backend/ERPCore/Domain/Enums/ItemType.cs

@@ -1,12 +0,0 @@
-namespace ERPCore.Domain.Enums;
-
-/// <summary>
-/// Item classification (FR-MD-01). Values match the <c>itemType</c> enum in
-/// docs/11-BACKEND-PHASE1.md §8. Stored as a string in the database.
-/// </summary>
-public enum ItemType
-{
-    Stocked,
-    NonStocked,
-    Service
-}

Backend/ERPCore/Domain/Enums/StockNature.cs

@@ -0,0 +1,14 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>
+/// Whether an item holds stock (FR-MD-01). Values match the <c>stockNature</c> enum in
+/// docs/11-BACKEND-PHASE1.md §8. Stored as a string in the database.
+/// Renamed from <c>ItemType</c> so that name could be taken by the ItemType master
+/// entity (Color/Size/Material) — the two concepts are unrelated (docs/10 Part C.9).
+/// </summary>
+public enum StockNature
+{
+    Stocked,
+    NonStocked,
+    Service
+}

Backend/ERPCore/Dtos/Brands/BrandDtos.cs

@@ -0,0 +1,26 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Brands;
+
+/// <summary>Brand resource (docs/11-BACKEND-PHASE1.md §2.6).</summary>
+public sealed record BrandDto(
+    int BrandId, string Name, EntityStatus Status, DateTime CreatedAt, DateTime? UpdatedAt);
+
+// Request DTOs — narrow: server-controlled fields (status, ids, timestamps)
+// are intentionally excluded to prevent over-posting (02-SECURITY B.6 / C.1). ----
+
+public sealed class CreateBrandRequest
+{
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+}
+
+public sealed class UpdateBrandRequest
+{
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+}
+
+public sealed class UpdateBrandStatusRequest
+{
+    [Required, EnumDataType(typeof(EntityStatus))] public EntityStatus Status { get; set; }
+}

Backend/ERPCore/Dtos/Categories/CategoryDtos.cs

@@ -1,15 +1,56 @@
 using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
 
 namespace ERPCore.Dtos.Categories;
 
-/// <summary>Flat category resource (docs/11-BACKEND-PHASE1.md §2.3).</summary>
-public sealed record CategoryDto(int CategoryId, string Name, int? ParentId);
+// Category (docs/11-BACKEND-PHASE1.md §2.3) ------------------------------------
+// The hierarchy is exactly two levels: Category → SubCategory. The former
+// self-nesting tree (parentId / ?tree=true / CategoryTreeDto) was removed in
+// migration #2 — see docs/10 Part C.1.
 
-/// <summary>Nested category node for <c>GET /categories?tree=true</c>.</summary>
-public sealed record CategoryTreeDto(int CategoryId, string Name, int? ParentId, IReadOnlyList<CategoryTreeDto> Children);
+/// <summary>Category resource — the top level.</summary>
+public sealed record CategoryDto(
+    int CategoryId, string Name, EntityStatus Status, DateTime CreatedAt, DateTime? UpdatedAt);
+
+/// <summary>Subcategory resource — the single optional level below a category.</summary>
+public sealed record SubCategoryDto(
+    int SubCategoryId, int CategoryId, string Name, EntityStatus Status,
+    DateTime CreatedAt, DateTime? UpdatedAt);
+
+// Request DTOs — narrow: server-controlled fields (status, ids, timestamps)
+// are intentionally excluded to prevent over-posting (02-SECURITY B.6 / C.1). ----
 
 public sealed class CreateCategoryRequest
 {
     [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
-    public int? ParentId { get; set; }
+}
+
+public sealed class UpdateCategoryRequest
+{
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+}
+
+public sealed class UpdateCategoryStatusRequest
+{
+    [Required, EnumDataType(typeof(EntityStatus))] public EntityStatus Status { get; set; }
+}
+
+/// <summary>Body for <c>POST /categories/{categoryId}/subcategories</c>; the parent comes from the route.</summary>
+public sealed class CreateSubCategoryRequest
+{
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+}
+
+/// <summary>
+/// Body for <c>PUT /subcategories/{id}</c>. Name only — a subcategory cannot be reparented,
+/// since moving one would silently invalidate the category of every item referencing it.
+/// </summary>
+public sealed class UpdateSubCategoryRequest
+{
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+}
+
+public sealed class UpdateSubCategoryStatusRequest
+{
+    [Required, EnumDataType(typeof(EntityStatus))] public EntityStatus Status { get; set; }
 }

Backend/ERPCore/Dtos/Config/ProductConfigDtos.cs

@@ -0,0 +1,27 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace ERPCore.Dtos.Config;
+
+/// <summary>
+/// Product configuration resource (docs/11-BACKEND-PHASE1.md §2.8). Singleton.
+/// <see cref="ItemTypesEnabled"/> is advisory (frontend-honoured) — see the entity docs.
+/// </summary>
+public sealed record ProductConfigDto(
+    bool SubcategoriesEnabled, bool BrandsEnabled, bool ItemTypesEnabled,
+    DateTime? UpdatedAt, int? UpdatedBy);
+
+/// <summary>
+/// Full replacement of the flags. <c>UpdatedBy</c> is derived from the token, never posted.
+/// <para>
+/// The flags are <see cref="bool"/>? deliberately: <c>[Required]</c> on a non-nullable bool
+/// is a no-op (it always has a value), so a body of <c>{}</c> would bind every flag to
+/// <c>false</c> and silently switch all three features off. Nullable makes the requirement
+/// actually bind — an omitted flag is a 400, not an accidental disable.
+/// </para>
+/// </summary>
+public sealed class UpdateProductConfigRequest
+{
+    [Required] public bool? SubcategoriesEnabled { get; set; }
+    [Required] public bool? BrandsEnabled { get; set; }
+    [Required] public bool? ItemTypesEnabled { get; set; }
+}

Backend/ERPCore/Dtos/ItemTypes/ItemTypeDtos.cs

@@ -0,0 +1,31 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.ItemTypes;
+
+/// <summary>
+/// Item type resource (docs/11-BACKEND-PHASE1.md §2.7) — a dimension name such as Color
+/// or Size. Carries no values and no item linkage: <c>GET /item-types</c> exists to
+/// populate the frontend builder's dropdown, and the chosen values are encoded into the
+/// client-generated SKU rather than stored (docs/10 Part C.9).
+/// </summary>
+public sealed record ItemTypeDto(
+    int ItemTypeId, string Name, EntityStatus Status, DateTime CreatedAt, DateTime? UpdatedAt);
+
+// Request DTOs — narrow: server-controlled fields (status, ids, timestamps)
+// are intentionally excluded to prevent over-posting (02-SECURITY B.6 / C.1). ----
+
+public sealed class CreateItemTypeRequest
+{
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+}
+
+public sealed class UpdateItemTypeRequest
+{
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+}
+
+public sealed class UpdateItemTypeStatusRequest
+{
+    [Required, EnumDataType(typeof(EntityStatus))] public EntityStatus Status { get; set; }
+}

Backend/ERPCore/Dtos/Items/ItemDtos.cs

@@ -7,8 +7,8 @@ namespace ERPCore.Dtos.Items;
 
 /// <summary>Row shape for <c>GET /items</c>.</summary>
 public sealed record ItemListItemDto(
-    int ItemId, string Sku, string Name, int CategoryId, int BaseUomId,
-    int? DefaultVendorId, ItemType ItemType, TrackingMode TrackingMode,
+    int ItemId, string Sku, string Name, int CategoryId, int? SubCategoryId, int? BrandId,
+    int BaseUomId, int? DefaultVendorId, StockNature StockNature, TrackingMode TrackingMode,
     string? TaxClass, EntityStatus Status);
 
 /// <summary>A single per-warehouse reorder policy row.</summary>
@@ -17,7 +17,8 @@ public sealed record ItemReorderDto(int WarehouseId, decimal ReorderPoint, decim
 /// <summary>Full item resource for <c>GET /items/{id}</c> and create/update responses.</summary>
 public sealed record ItemDetailDto(
     int ItemId, string Sku, string Name, string? Description, int CategoryId,
-    int BaseUomId, int? DefaultVendorId, ItemType ItemType, TrackingMode TrackingMode,
+    int? SubCategoryId, int? BrandId, int BaseUomId, int? DefaultVendorId,
+    StockNature StockNature, TrackingMode TrackingMode,
     string? TaxClass, EntityStatus Status, IReadOnlyList<ItemReorderDto> Reorder,
     DateTime CreatedAt, DateTime? UpdatedAt);
 
@@ -33,15 +34,23 @@ public sealed record ItemReorderSettingsDto(IReadOnlyList<ItemReorderDto> Settin
 // Request DTOs — narrow: server-controlled fields (status, ids, timestamps)
 // are intentionally excluded to prevent over-posting (02-SECURITY B.6 / C.1). ----
 
+// Note: the SKU is generated client-side (it encodes the chosen item-type values, e.g.
+// "BL-100-0003"); the server only enforces uniqueness. There is no item-type field here
+// by design — items carry no item-type reference (docs/10 Part C.9).
+
 public sealed class CreateItemRequest
 {
     [Required, StringLength(50)] public string Sku { get; set; } = string.Empty;
     [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
     [StringLength(1000)] public string? Description { get; set; }
     [Required] public int CategoryId { get; set; }
+    /// <summary>Optional; must belong to <see cref="CategoryId"/>. Rejected when subcategories are disabled.</summary>
+    public int? SubCategoryId { get; set; }
+    /// <summary>Optional. Rejected when brands are disabled.</summary>
+    public int? BrandId { get; set; }
     [Required] public int BaseUomId { get; set; }
     public int? DefaultVendorId { get; set; }
-    [Required, EnumDataType(typeof(ItemType))] public ItemType ItemType { get; set; }
+    [Required, EnumDataType(typeof(StockNature))] public StockNature StockNature { get; set; }
     [EnumDataType(typeof(TrackingMode))] public TrackingMode TrackingMode { get; set; } = TrackingMode.None;
     [StringLength(20)] public string? TaxClass { get; set; }
 }
@@ -52,9 +61,13 @@ public sealed class UpdateItemRequest
     [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
     [StringLength(1000)] public string? Description { get; set; }
     [Required] public int CategoryId { get; set; }
+    /// <summary>Optional; must belong to <see cref="CategoryId"/>. Rejected when subcategories are disabled.</summary>
+    public int? SubCategoryId { get; set; }
+    /// <summary>Optional. Rejected when brands are disabled.</summary>
+    public int? BrandId { get; set; }
     [Required] public int BaseUomId { get; set; }
     public int? DefaultVendorId { get; set; }
-    [Required, EnumDataType(typeof(ItemType))] public ItemType ItemType { get; set; }
+    [Required, EnumDataType(typeof(StockNature))] public StockNature StockNature { get; set; }
     [EnumDataType(typeof(TrackingMode))] public TrackingMode TrackingMode { get; set; } = TrackingMode.None;
     [StringLength(20)] public string? TaxClass { get; set; }
 }

Backend/ERPCore/Infra/Persistence/Configurations/BrandConfiguration.cs

@@ -0,0 +1,29 @@
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ERPCore.Infra.Persistence.Configurations;
+
+public sealed class BrandConfiguration : IEntityTypeConfiguration<Brand>
+{
+    public void Configure(EntityTypeBuilder<Brand> builder)
+    {
+        builder.ToTable("brands");
+        builder.HasKey(b => b.BrandId);
+
+        builder.Property(b => b.Name).IsRequired().HasMaxLength(200);
+        builder.HasIndex(b => b.Name).IsUnique();
+
+        builder.Property(b => b.Status)
+            .HasConversion<string>().HasMaxLength(20).IsRequired()
+            .HasDefaultValue(EntityStatus.Active);
+
+        builder.Property(b => b.CreatedAt).IsRequired();
+
+        // PostgreSQL xmin system column as the optimistic concurrency token (ETag).
+        builder.Property(b => b.RowVersion).IsRowVersion();
+
+        builder.HasIndex(b => b.Status);
+    }
+}

Backend/ERPCore/Infra/Persistence/Configurations/CategoryConfiguration.cs

@@ -1,4 +1,5 @@
 using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Metadata.Builders;
 
@@ -12,12 +13,17 @@ public sealed class CategoryConfiguration : IEntityTypeConfiguration<Category>
         builder.HasKey(c => c.CategoryId);
 
         builder.Property(c => c.Name).IsRequired().HasMaxLength(200);
+        builder.HasIndex(c => c.Name).IsUnique();
 
-        builder.HasOne(c => c.Parent)
-            .WithMany(c => c.Children)
-            .HasForeignKey(c => c.ParentId)
-            .OnDelete(DeleteBehavior.Restrict);
+        builder.Property(c => c.Status)
+            .HasConversion<string>().HasMaxLength(20).IsRequired()
+            .HasDefaultValue(EntityStatus.Active);
 
-        builder.HasIndex(c => c.ParentId);
+        builder.Property(c => c.CreatedAt).IsRequired();
+
+        // PostgreSQL xmin system column as the optimistic concurrency token (ETag).
+        builder.Property(c => c.RowVersion).IsRowVersion();
+
+        builder.HasIndex(c => c.Status);
     }
 }

Backend/ERPCore/Infra/Persistence/Configurations/ItemConfiguration.cs

@@ -19,7 +19,7 @@ public sealed class ItemConfiguration : IEntityTypeConfiguration<Item>
         builder.Property(i => i.Description).HasMaxLength(1000);
         builder.Property(i => i.TaxClass).HasMaxLength(20);
 
-        builder.Property(i => i.ItemType)
+        builder.Property(i => i.StockNature)
             .HasConversion<string>().HasMaxLength(20).IsRequired();
         builder.Property(i => i.TrackingMode)
             .HasConversion<string>().HasMaxLength(20).IsRequired();
@@ -37,6 +37,16 @@ public sealed class ItemConfiguration : IEntityTypeConfiguration<Item>
             .HasForeignKey(i => i.CategoryId)
             .OnDelete(DeleteBehavior.Restrict);
 
+        builder.HasOne(i => i.SubCategory)
+            .WithMany()
+            .HasForeignKey(i => i.SubCategoryId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        builder.HasOne(i => i.Brand)
+            .WithMany()
+            .HasForeignKey(i => i.BrandId)
+            .OnDelete(DeleteBehavior.Restrict);
+
         builder.HasOne(i => i.BaseUom)
             .WithMany()
             .HasForeignKey(i => i.BaseUomId)
@@ -49,5 +59,6 @@ public sealed class ItemConfiguration : IEntityTypeConfiguration<Item>
 
         builder.HasIndex(i => i.Status);
         builder.HasIndex(i => i.CategoryId);
+        builder.HasIndex(i => i.BrandId);
     }
 }

Backend/ERPCore/Infra/Persistence/Configurations/ItemTypeConfiguration.cs

@@ -0,0 +1,33 @@
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ERPCore.Infra.Persistence.Configurations;
+
+/// <summary>
+/// Configures the ItemType master (Color/Size/Material). Note there are deliberately no
+/// relationships here — nothing references this table (docs/10 Part C.9).
+/// </summary>
+public sealed class ItemTypeConfiguration : IEntityTypeConfiguration<ItemType>
+{
+    public void Configure(EntityTypeBuilder<ItemType> builder)
+    {
+        builder.ToTable("item_types");
+        builder.HasKey(t => t.ItemTypeId);
+
+        builder.Property(t => t.Name).IsRequired().HasMaxLength(200);
+        builder.HasIndex(t => t.Name).IsUnique();
+
+        builder.Property(t => t.Status)
+            .HasConversion<string>().HasMaxLength(20).IsRequired()
+            .HasDefaultValue(EntityStatus.Active);
+
+        builder.Property(t => t.CreatedAt).IsRequired();
+
+        // PostgreSQL xmin system column as the optimistic concurrency token (ETag).
+        builder.Property(t => t.RowVersion).IsRowVersion();
+
+        builder.HasIndex(t => t.Status);
+    }
+}

Backend/ERPCore/Infra/Persistence/Configurations/ProductConfigConfiguration.cs

@@ -0,0 +1,37 @@
+using ERPCore.Domain.Entities;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ERPCore.Infra.Persistence.Configurations;
+
+/// <summary>
+/// Configures the singleton product-configuration row (FR-MD-11). The check constraint
+/// is what makes "singleton" a database guarantee rather than a convention.
+/// </summary>
+public sealed class ProductConfigConfiguration : IEntityTypeConfiguration<ProductConfig>
+{
+    public void Configure(EntityTypeBuilder<ProductConfig> builder)
+    {
+        // The column is created as quoted PascalCase ("ConfigId"), so the constraint must
+        // quote it too — an unquoted config_id would fold to a column that does not exist.
+        builder.ToTable("product_config", t =>
+            t.HasCheckConstraint("ck_product_config_singleton", $"\"ConfigId\" = {ProductConfig.SingletonId}"));
+
+        builder.HasKey(c => c.ConfigId);
+
+        // The id is fixed, never generated — there is exactly one row, seeded by DataSeeder.
+        builder.Property(c => c.ConfigId).ValueGeneratedNever();
+
+        builder.Property(c => c.SubcategoriesEnabled).IsRequired().HasDefaultValue(true);
+        builder.Property(c => c.BrandsEnabled).IsRequired().HasDefaultValue(true);
+        builder.Property(c => c.ItemTypesEnabled).IsRequired().HasDefaultValue(true);
+
+        // PostgreSQL xmin system column as the optimistic concurrency token (ETag).
+        builder.Property(c => c.RowVersion).IsRowVersion();
+
+        builder.HasOne(c => c.UpdatedByUser)
+            .WithMany()
+            .HasForeignKey(c => c.UpdatedBy)
+            .OnDelete(DeleteBehavior.Restrict);
+    }
+}

Backend/ERPCore/Infra/Persistence/Configurations/SubCategoryConfiguration.cs

@@ -0,0 +1,35 @@
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ERPCore.Infra.Persistence.Configurations;
+
+public sealed class SubCategoryConfiguration : IEntityTypeConfiguration<SubCategory>
+{
+    public void Configure(EntityTypeBuilder<SubCategory> builder)
+    {
+        builder.ToTable("subcategories");
+        builder.HasKey(s => s.SubCategoryId);
+
+        builder.Property(s => s.Name).IsRequired().HasMaxLength(200);
+
+        builder.Property(s => s.Status)
+            .HasConversion<string>().HasMaxLength(20).IsRequired()
+            .HasDefaultValue(EntityStatus.Active);
+
+        builder.Property(s => s.CreatedAt).IsRequired();
+
+        // PostgreSQL xmin system column as the optimistic concurrency token (ETag).
+        builder.Property(s => s.RowVersion).IsRowVersion();
+
+        builder.HasOne(s => s.Category)
+            .WithMany(c => c.SubCategories)
+            .HasForeignKey(s => s.CategoryId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        // Names need only be unique within their parent category.
+        builder.HasIndex(s => new { s.CategoryId, s.Name }).IsUnique();
+        builder.HasIndex(s => s.Status);
+    }
+}

Backend/ERPCore/Infra/Persistence/DataSeeder.cs

@@ -12,6 +12,13 @@ namespace ERPCore.Infra.Persistence;
 /// </summary>
 public static class DataSeeder
 {
+    /// <summary>
+    /// Item type names the frontend builder has always assumed exist (they were hardcoded
+    /// while it ran on mock data). Seeded so the dropdown is not empty on a fresh database;
+    /// users add their own (e.g. Material) from the admin screen.
+    /// </summary>
+    private static readonly string[] StandardItemTypes = ["Color", "Size"];
+
     private static readonly (string Code, string Description, ReasonContext Context)[] StandardReasonCodes =
     [
         ("DMG", "Damage", ReasonContext.Adjustment),
@@ -26,6 +33,15 @@ public static class DataSeeder
     ];
 
     public static async Task SeedAsync(ErpDbContext db, CancellationToken ct = default)
+    {
+        var dirty = await SeedReasonCodesAsync(db, ct);
+        dirty |= await SeedItemTypesAsync(db, ct);
+        dirty |= await SeedProductConfigAsync(db, ct);
+
+        if (dirty) await db.SaveChangesAsync(ct);
+    }
+
+    private static async Task<bool> SeedReasonCodesAsync(ErpDbContext db, CancellationToken ct)
     {
         var existing = await db.ReasonCodes
             .Select(r => new { r.Context, r.Code })
@@ -37,9 +53,44 @@ public static class DataSeeder
             .Select(r => new ReasonCode { Code = r.Code, Description = r.Description, Context = r.Context })
             .ToList();
 
-        if (toAdd.Count == 0) return;
+        if (toAdd.Count == 0) return false;
 
         db.ReasonCodes.AddRange(toAdd);
-        await db.SaveChangesAsync(ct);
+        return true;
+    }
+
+    private static async Task<bool> SeedItemTypesAsync(ErpDbContext db, CancellationToken ct)
+    {
+        var have = await db.ItemTypes.Select(t => t.Name).ToListAsync(ct);
+
+        var toAdd = StandardItemTypes
+            .Where(name => !have.Contains(name, StringComparer.OrdinalIgnoreCase))
+            .Select(name => new ItemType { Name = name, Status = EntityStatus.Active, CreatedAt = DateTime.UtcNow })
+            .ToList();
+
+        if (toAdd.Count == 0) return false;
+
+        db.ItemTypes.AddRange(toAdd);
+        return true;
+    }
+
+    /// <summary>
+    /// Ensures the singleton product-config row exists (FR-MD-11). Migration #2 inserts it,
+    /// so this only fires for a database built some other way — but without it every Item
+    /// write would 404 on the missing config, so it is worth the one query at startup.
+    /// New deployments start with all features on.
+    /// </summary>
+    private static async Task<bool> SeedProductConfigAsync(ErpDbContext db, CancellationToken ct)
+    {
+        if (await db.ProductConfig.AnyAsync(c => c.ConfigId == ProductConfig.SingletonId, ct)) return false;
+
+        db.ProductConfig.Add(new ProductConfig
+        {
+            ConfigId = ProductConfig.SingletonId,
+            SubcategoriesEnabled = true,
+            BrandsEnabled = true,
+            ItemTypesEnabled = true
+        });
+        return true;
     }
 }

Backend/ERPCore/Infra/Persistence/ErpDbContext.cs

@@ -6,7 +6,7 @@ using Microsoft.EntityFrameworkCore;
 namespace ERPCore.Infra.Persistence;
 
 /// <summary>
-/// EF Core context for the ERP database. The 38 Phase 1 entities and their
+/// EF Core context for the ERP database. The 42 Phase 1 entities and their
 /// <see cref="IEntityTypeConfiguration{TEntity}"/> configurations are added under
 /// Domain/Entities and Infra/Persistence/Configurations as they are implemented.
 /// The authoritative schema lives in docs/10-BACKEND-PHASE1.md — do not invent it here.
@@ -23,6 +23,10 @@ public class ErpDbContext : DbContext
 
     // --- Master Data (docs/10 Part C.1) ---
     public DbSet<Category> Categories => Set<Category>();
+    public DbSet<SubCategory> SubCategories => Set<SubCategory>();
+    public DbSet<Brand> Brands => Set<Brand>();
+    /// <summary>Color/Size/Material dimension names. Unlinked to Item by design (docs/10 C.9).</summary>
+    public DbSet<ItemType> ItemTypes => Set<ItemType>();
     public DbSet<Uom> Uoms => Set<Uom>();
     public DbSet<UomConversion> UomConversions => Set<UomConversion>();
     public DbSet<Item> Items => Set<Item>();
@@ -30,6 +34,8 @@ public class ErpDbContext : DbContext
     public DbSet<Vendor> Vendors => Set<Vendor>();
     public DbSet<Warehouse> Warehouses => Set<Warehouse>();
     public DbSet<Bin> Bins => Set<Bin>();
+    /// <summary>Singleton row (FR-MD-11).</summary>
+    public DbSet<ProductConfig> ProductConfig => Set<ProductConfig>();
 
     // --- Cross-cutting (docs/10 Part C.7) ---
     public DbSet<User> Users => Set<User>();

Backend/ERPCore/Infra/Persistence/Migrations/20260716134938_AddBrandsSubcategoriesItemTypesAndProductConfig.cs

@@ -0,0 +1,442 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+
+#nullable disable
+
+namespace ERPCore.Infra.Persistence.Migrations
+{
+    /// <summary>
+    /// Adds the Brand / SubCategory / ItemType masters and the singleton product config,
+    /// and converts CATEGORY from a self-nesting tree into a fixed two-level
+    /// Category → SubCategory hierarchy (docs/10 Part C.1).
+    /// <para>
+    /// <b>This migration carries data, not just DDL.</b> The scaffolded version dropped
+    /// <c>categories.ParentId</c> outright, which would have silently flattened every
+    /// child category into a root and left items pointing at what is now a top-level
+    /// category — losing the parent entirely. The hand-written steps below (marked
+    /// "data migration") move child categories into <c>subcategories</c> and repoint items
+    /// onto the correct (category, subcategory) pair before the column goes away.
+    /// </para>
+    /// </summary>
+    public partial class AddBrandsSubcategoriesItemTypesAndProductConfig : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            // NOTE: the ParentId drop is deliberately deferred to the bottom of this method —
+            // the data migration reads it. Order here is load-bearing.
+            migrationBuilder.RenameColumn(
+                name: "ItemType",
+                table: "items",
+                newName: "StockNature");
+
+            migrationBuilder.AddColumn<int>(
+                name: "BrandId",
+                table: "items",
+                type: "integer",
+                nullable: true);
+
+            migrationBuilder.AddColumn<int>(
+                name: "SubCategoryId",
+                table: "items",
+                type: "integer",
+                nullable: true);
+
+            migrationBuilder.AddColumn<DateTime>(
+                name: "CreatedAt",
+                table: "categories",
+                type: "timestamp with time zone",
+                nullable: false,
+                defaultValue: new DateTime(1, 1, 1, 0, 0, 0, 0, DateTimeKind.Unspecified));
+
+            migrationBuilder.AddColumn<string>(
+                name: "Status",
+                table: "categories",
+                type: "character varying(20)",
+                maxLength: 20,
+                nullable: false,
+                defaultValue: "Active");
+
+            migrationBuilder.AddColumn<DateTime>(
+                name: "UpdatedAt",
+                table: "categories",
+                type: "timestamp with time zone",
+                nullable: true);
+
+            migrationBuilder.AddColumn<uint>(
+                name: "xmin",
+                table: "categories",
+                type: "xid",
+                rowVersion: true,
+                nullable: false,
+                defaultValue: 0u);
+
+            migrationBuilder.CreateTable(
+                name: "brands",
+                columns: table => new
+                {
+                    BrandId = table.Column<int>(type: "integer", nullable: false)
+                        .Annotation("Npgsql:ValueGenerationStrategy", NpgsqlValueGenerationStrategy.IdentityByDefaultColumn),
+                    Name = table.Column<string>(type: "character varying(200)", maxLength: 200, nullable: false),
+                    Status = table.Column<string>(type: "character varying(20)", maxLength: 20, nullable: false, defaultValue: "Active"),
+                    CreatedAt = table.Column<DateTime>(type: "timestamp with time zone", nullable: false),
+                    UpdatedAt = table.Column<DateTime>(type: "timestamp with time zone", nullable: true),
+                    xmin = table.Column<uint>(type: "xid", rowVersion: true, nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_brands", x => x.BrandId);
+                });
+
+            migrationBuilder.CreateTable(
+                name: "item_types",
+                columns: table => new
+                {
+                    ItemTypeId = table.Column<int>(type: "integer", nullable: false)
+                        .Annotation("Npgsql:ValueGenerationStrategy", NpgsqlValueGenerationStrategy.IdentityByDefaultColumn),
+                    Name = table.Column<string>(type: "character varying(200)", maxLength: 200, nullable: false),
+                    Status = table.Column<string>(type: "character varying(20)", maxLength: 20, nullable: false, defaultValue: "Active"),
+                    CreatedAt = table.Column<DateTime>(type: "timestamp with time zone", nullable: false),
+                    UpdatedAt = table.Column<DateTime>(type: "timestamp with time zone", nullable: true),
+                    xmin = table.Column<uint>(type: "xid", rowVersion: true, nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_item_types", x => x.ItemTypeId);
+                });
+
+            migrationBuilder.CreateTable(
+                name: "product_config",
+                columns: table => new
+                {
+                    ConfigId = table.Column<int>(type: "integer", nullable: false),
+                    SubcategoriesEnabled = table.Column<bool>(type: "boolean", nullable: false, defaultValue: true),
+                    BrandsEnabled = table.Column<bool>(type: "boolean", nullable: false, defaultValue: true),
+                    ItemTypesEnabled = table.Column<bool>(type: "boolean", nullable: false, defaultValue: true),
+                    UpdatedAt = table.Column<DateTime>(type: "timestamp with time zone", nullable: true),
+                    UpdatedBy = table.Column<int>(type: "integer", nullable: true),
+                    xmin = table.Column<uint>(type: "xid", rowVersion: true, nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_product_config", x => x.ConfigId);
+                    table.CheckConstraint("ck_product_config_singleton", "\"ConfigId\" = 1");
+                    table.ForeignKey(
+                        name: "FK_product_config_users_UpdatedBy",
+                        column: x => x.UpdatedBy,
+                        principalTable: "users",
+                        principalColumn: "UserId",
+                        onDelete: ReferentialAction.Restrict);
+                });
+
+            migrationBuilder.CreateTable(
+                name: "subcategories",
+                columns: table => new
+                {
+                    SubCategoryId = table.Column<int>(type: "integer", nullable: false)
+                        .Annotation("Npgsql:ValueGenerationStrategy", NpgsqlValueGenerationStrategy.IdentityByDefaultColumn),
+                    Name = table.Column<string>(type: "character varying(200)", maxLength: 200, nullable: false),
+                    CategoryId = table.Column<int>(type: "integer", nullable: false),
+                    Status = table.Column<string>(type: "character varying(20)", maxLength: 20, nullable: false, defaultValue: "Active"),
+                    CreatedAt = table.Column<DateTime>(type: "timestamp with time zone", nullable: false),
+                    UpdatedAt = table.Column<DateTime>(type: "timestamp with time zone", nullable: true),
+                    xmin = table.Column<uint>(type: "xid", rowVersion: true, nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_subcategories", x => x.SubCategoryId);
+                    table.ForeignKey(
+                        name: "FK_subcategories_categories_CategoryId",
+                        column: x => x.CategoryId,
+                        principalTable: "categories",
+                        principalColumn: "CategoryId",
+                        onDelete: ReferentialAction.Restrict);
+                });
+
+            // ---------------------------------------------------------------------------
+            // DATA MIGRATION — must run before ParentId is dropped.
+            // ---------------------------------------------------------------------------
+
+            // Existing categories predate CreatedAt; the added column defaulted them to
+            // 0001-01-01. Stamp them with the migration time instead of a sentinel date.
+            migrationBuilder.Sql(@"
+                UPDATE categories SET ""CreatedAt"" = NOW() AT TIME ZONE 'utc';
+            ");
+
+            // Carry the old category id alongside each new subcategory so items can be
+            // repointed by join below. Dropped again once the repoint is done.
+            migrationBuilder.Sql(@"
+                ALTER TABLE subcategories ADD COLUMN legacy_category_id integer;
+            ");
+
+            // Walk the old tree to its roots. The previous model allowed unlimited nesting,
+            // but the new one is exactly two levels — so a category at any depth below the
+            // root collapses into a subcategory of its ROOT ancestor (a grandchild cannot
+            // become a subcategory of its immediate parent, since that parent is itself
+            // ceasing to be a category).
+            migrationBuilder.Sql(@"
+                WITH RECURSIVE tree AS (
+                    SELECT ""CategoryId"", ""ParentId"", ""Name"", ""CategoryId"" AS root_id
+                    FROM categories
+                    WHERE ""ParentId"" IS NULL
+                    UNION ALL
+                    SELECT c.""CategoryId"", c.""ParentId"", c.""Name"", t.root_id
+                    FROM categories c
+                    JOIN tree t ON c.""ParentId"" = t.""CategoryId""
+                )
+                INSERT INTO subcategories (""Name"", ""CategoryId"", ""Status"", ""CreatedAt"", legacy_category_id)
+                SELECT t.""Name"", t.root_id, 'Active', NOW() AT TIME ZONE 'utc', t.""CategoryId""
+                FROM tree t
+                WHERE t.""ParentId"" IS NOT NULL;
+            ");
+
+            // Repoint items: an item that pointed at a child category now carries the root
+            // category plus the subcategory it actually meant.
+            migrationBuilder.Sql(@"
+                UPDATE items i
+                SET ""SubCategoryId"" = s.""SubCategoryId"",
+                    ""CategoryId""    = s.""CategoryId""
+                FROM subcategories s
+                WHERE s.legacy_category_id = i.""CategoryId"";
+            ");
+
+            // The self-FK must go before the delete, or RESTRICT rejects removing a parent
+            // whose own child row is still present.
+            migrationBuilder.DropForeignKey(
+                name: "FK_categories_categories_ParentId",
+                table: "categories");
+
+            // Every non-root category now lives in `subcategories`, and no item references
+            // one any more (repointed above), so the rows can go.
+            migrationBuilder.Sql(@"
+                DELETE FROM categories WHERE ""ParentId"" IS NOT NULL;
+                ALTER TABLE subcategories DROP COLUMN legacy_category_id;
+            ");
+
+            migrationBuilder.DropIndex(
+                name: "IX_categories_ParentId",
+                table: "categories");
+
+            migrationBuilder.DropColumn(
+                name: "ParentId",
+                table: "categories");
+
+            // Seed the singleton config (FR-MD-11) — all features on. Item writes read this
+            // row, so it must exist before the app serves a single request.
+            migrationBuilder.Sql(@"
+                INSERT INTO product_config (""ConfigId"", ""SubcategoriesEnabled"", ""BrandsEnabled"", ""ItemTypesEnabled"")
+                VALUES (1, TRUE, TRUE, TRUE)
+                ON CONFLICT (""ConfigId"") DO NOTHING;
+            ");
+
+            // ---------------------------------------------------------------------------
+
+            migrationBuilder.CreateIndex(
+                name: "IX_items_BrandId",
+                table: "items",
+                column: "BrandId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_items_SubCategoryId",
+                table: "items",
+                column: "SubCategoryId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_categories_Name",
+                table: "categories",
+                column: "Name",
+                unique: true);
+
+            migrationBuilder.CreateIndex(
+                name: "IX_categories_Status",
+                table: "categories",
+                column: "Status");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_brands_Name",
+                table: "brands",
+                column: "Name",
+                unique: true);
+
+            migrationBuilder.CreateIndex(
+                name: "IX_brands_Status",
+                table: "brands",
+                column: "Status");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_item_types_Name",
+                table: "item_types",
+                column: "Name",
+                unique: true);
+
+            migrationBuilder.CreateIndex(
+                name: "IX_item_types_Status",
+                table: "item_types",
+                column: "Status");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_product_config_UpdatedBy",
+                table: "product_config",
+                column: "UpdatedBy");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_subcategories_CategoryId_Name",
+                table: "subcategories",
+                columns: new[] { "CategoryId", "Name" },
+                unique: true);
+
+            migrationBuilder.CreateIndex(
+                name: "IX_subcategories_Status",
+                table: "subcategories",
+                column: "Status");
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_items_brands_BrandId",
+                table: "items",
+                column: "BrandId",
+                principalTable: "brands",
+                principalColumn: "BrandId",
+                onDelete: ReferentialAction.Restrict);
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_items_subcategories_SubCategoryId",
+                table: "items",
+                column: "SubCategoryId",
+                principalTable: "subcategories",
+                principalColumn: "SubCategoryId",
+                onDelete: ReferentialAction.Restrict);
+        }
+
+        /// <summary>
+        /// Reverses the schema change and puts the subcategory data back where it came from.
+        /// <para>
+        /// The scaffolded version simply dropped <c>subcategories</c>, which would have
+        /// discarded exactly what <see cref="Up"/> preserved. Instead each subcategory is
+        /// restored as a child category and its items are repointed back onto it. This is
+        /// not perfectly lossless: the old tree's depth is gone (a former grandchild comes
+        /// back as a direct child of its root), and Brand data cannot survive a schema that
+        /// has nowhere to put it.
+        /// </para>
+        /// </summary>
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropForeignKey(
+                name: "FK_items_brands_BrandId",
+                table: "items");
+
+            migrationBuilder.DropForeignKey(
+                name: "FK_items_subcategories_SubCategoryId",
+                table: "items");
+
+            // Restore the parent column + self-FK first so subcategories have somewhere to
+            // land, then move them back before the table is dropped.
+            migrationBuilder.AddColumn<int>(
+                name: "ParentId",
+                table: "categories",
+                type: "integer",
+                nullable: true);
+
+            // ---------------------------------------------------------------------------
+            // DATA MIGRATION (reverse) — must run before `subcategories` is dropped.
+            // ---------------------------------------------------------------------------
+
+            migrationBuilder.Sql(@"
+                ALTER TABLE categories ADD COLUMN legacy_subcategory_id integer;
+            ");
+
+            // Each subcategory becomes a child category again under the same parent.
+            migrationBuilder.Sql(@"
+                INSERT INTO categories (""Name"", ""ParentId"", ""CreatedAt"", ""Status"", legacy_subcategory_id)
+                SELECT s.""Name"", s.""CategoryId"", s.""CreatedAt"", s.""Status"", s.""SubCategoryId""
+                FROM subcategories s;
+            ");
+
+            // Items that carried a subcategory point back at the restored child category.
+            migrationBuilder.Sql(@"
+                UPDATE items i
+                SET ""CategoryId"" = c.""CategoryId""
+                FROM categories c
+                WHERE c.legacy_subcategory_id = i.""SubCategoryId"";
+            ");
+
+            migrationBuilder.Sql(@"
+                ALTER TABLE categories DROP COLUMN legacy_subcategory_id;
+            ");
+
+            // ---------------------------------------------------------------------------
+
+            migrationBuilder.DropTable(
+                name: "brands");
+
+            migrationBuilder.DropTable(
+                name: "item_types");
+
+            migrationBuilder.DropTable(
+                name: "product_config");
+
+            migrationBuilder.DropTable(
+                name: "subcategories");
+
+            migrationBuilder.DropIndex(
+                name: "IX_items_BrandId",
+                table: "items");
+
+            migrationBuilder.DropIndex(
+                name: "IX_items_SubCategoryId",
+                table: "items");
+
+            migrationBuilder.DropIndex(
+                name: "IX_categories_Name",
+                table: "categories");
+
+            migrationBuilder.DropIndex(
+                name: "IX_categories_Status",
+                table: "categories");
+
+            migrationBuilder.DropColumn(
+                name: "BrandId",
+                table: "items");
+
+            migrationBuilder.DropColumn(
+                name: "SubCategoryId",
+                table: "items");
+
+            migrationBuilder.DropColumn(
+                name: "CreatedAt",
+                table: "categories");
+
+            migrationBuilder.DropColumn(
+                name: "Status",
+                table: "categories");
+
+            migrationBuilder.DropColumn(
+                name: "UpdatedAt",
+                table: "categories");
+
+            migrationBuilder.DropColumn(
+                name: "xmin",
+                table: "categories");
+
+            migrationBuilder.RenameColumn(
+                name: "StockNature",
+                table: "items",
+                newName: "ItemType");
+
+            // ParentId itself was re-added at the top of this method, ahead of the reverse
+            // data migration that populates it.
+            migrationBuilder.CreateIndex(
+                name: "IX_categories_ParentId",
+                table: "categories",
+                column: "ParentId");
+
+            migrationBuilder.AddForeignKey(
+                name: "FK_categories_categories_ParentId",
+                table: "categories",
+                column: "ParentId",
+                principalTable: "categories",
+                principalColumn: "CategoryId",
+                onDelete: ReferentialAction.Restrict);
+        }
+    }
+}

Backend/ERPCore/Infra/Persistence/Migrations/ErpDbContextModelSnapshot.cs

@@ -119,6 +119,48 @@ namespace ERPCore.Infra.Persistence.Migrations
                     b.ToTable("bins", (string)null);
                 });
 
+            modelBuilder.Entity("ERPCore.Domain.Entities.Brand", b =>
+                {
+                    b.Property<int>("BrandId")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("BrandId"));
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("Name")
+                        .IsRequired()
+                        .HasMaxLength(200)
+                        .HasColumnType("character varying(200)");
+
+                    b.Property<uint>("RowVersion")
+                        .IsConcurrencyToken()
+                        .ValueGeneratedOnAddOrUpdate()
+                        .HasColumnType("xid")
+                        .HasColumnName("xmin");
+
+                    b.Property<string>("Status")
+                        .IsRequired()
+                        .ValueGeneratedOnAdd()
+                        .HasMaxLength(20)
+                        .HasColumnType("character varying(20)")
+                        .HasDefaultValue("Active");
+
+                    b.Property<DateTime?>("UpdatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.HasKey("BrandId");
+
+                    b.HasIndex("Name")
+                        .IsUnique();
+
+                    b.HasIndex("Status");
+
+                    b.ToTable("brands", (string)null);
+                });
+
             modelBuilder.Entity("ERPCore.Domain.Entities.Category", b =>
                 {
                     b.Property<int>("CategoryId")
@@ -127,17 +169,36 @@ namespace ERPCore.Infra.Persistence.Migrations
 
                     NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("CategoryId"));
 
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
                     b.Property<string>("Name")
                         .IsRequired()
                         .HasMaxLength(200)
                         .HasColumnType("character varying(200)");
 
-                    b.Property<int?>("ParentId")
-                        .HasColumnType("integer");
+                    b.Property<uint>("RowVersion")
+                        .IsConcurrencyToken()
+                        .ValueGeneratedOnAddOrUpdate()
+                        .HasColumnType("xid")
+                        .HasColumnName("xmin");
+
+                    b.Property<string>("Status")
+                        .IsRequired()
+                        .ValueGeneratedOnAdd()
+                        .HasMaxLength(20)
+                        .HasColumnType("character varying(20)")
+                        .HasDefaultValue("Active");
+
+                    b.Property<DateTime?>("UpdatedAt")
+                        .HasColumnType("timestamp with time zone");
 
                     b.HasKey("CategoryId");
 
-                    b.HasIndex("ParentId");
+                    b.HasIndex("Name")
+                        .IsUnique();
+
+                    b.HasIndex("Status");
 
                     b.ToTable("categories", (string)null);
                 });
@@ -273,6 +334,9 @@ namespace ERPCore.Infra.Persistence.Migrations
                     b.Property<int>("BaseUomId")
                         .HasColumnType("integer");
 
+                    b.Property<int?>("BrandId")
+                        .HasColumnType("integer");
+
                     b.Property<int>("CategoryId")
                         .HasColumnType("integer");
 
@@ -286,11 +350,6 @@ namespace ERPCore.Infra.Persistence.Migrations
                         .HasMaxLength(1000)
                         .HasColumnType("character varying(1000)");
 
-                    b.Property<string>("ItemType")
-                        .IsRequired()
-                        .HasMaxLength(20)
-                        .HasColumnType("character varying(20)");
-
                     b.Property<string>("Name")
                         .IsRequired()
                         .HasMaxLength(200)
@@ -314,6 +373,14 @@ namespace ERPCore.Infra.Persistence.Migrations
                         .HasColumnType("character varying(20)")
                         .HasDefaultValue("Active");
 
+                    b.Property<string>("StockNature")
+                        .IsRequired()
+                        .HasMaxLength(20)
+                        .HasColumnType("character varying(20)");
+
+                    b.Property<int?>("SubCategoryId")
+                        .HasColumnType("integer");
+
                     b.Property<string>("TaxClass")
                         .HasMaxLength(20)
                         .HasColumnType("character varying(20)");
@@ -330,6 +397,8 @@ namespace ERPCore.Infra.Persistence.Migrations
 
                     b.HasIndex("BaseUomId");
 
+                    b.HasIndex("BrandId");
+
                     b.HasIndex("CategoryId");
 
                     b.HasIndex("DefaultVendorId");
@@ -339,6 +408,8 @@ namespace ERPCore.Infra.Persistence.Migrations
 
                     b.HasIndex("Status");
 
+                    b.HasIndex("SubCategoryId");
+
                     b.ToTable("items", (string)null);
                 });
 
@@ -374,6 +445,48 @@ namespace ERPCore.Infra.Persistence.Migrations
                     b.ToTable("item_reorders", (string)null);
                 });
 
+            modelBuilder.Entity("ERPCore.Domain.Entities.ItemType", b =>
+                {
+                    b.Property<int>("ItemTypeId")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("ItemTypeId"));
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("Name")
+                        .IsRequired()
+                        .HasMaxLength(200)
+                        .HasColumnType("character varying(200)");
+
+                    b.Property<uint>("RowVersion")
+                        .IsConcurrencyToken()
+                        .ValueGeneratedOnAddOrUpdate()
+                        .HasColumnType("xid")
+                        .HasColumnName("xmin");
+
+                    b.Property<string>("Status")
+                        .IsRequired()
+                        .ValueGeneratedOnAdd()
+                        .HasMaxLength(20)
+                        .HasColumnType("character varying(20)")
+                        .HasDefaultValue("Active");
+
+                    b.Property<DateTime?>("UpdatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.HasKey("ItemTypeId");
+
+                    b.HasIndex("Name")
+                        .IsUnique();
+
+                    b.HasIndex("Status");
+
+                    b.ToTable("item_types", (string)null);
+                });
+
             modelBuilder.Entity("ERPCore.Domain.Entities.JournalEntryStub", b =>
                 {
                     b.Property<int>("JournalId")
@@ -490,6 +603,48 @@ namespace ERPCore.Infra.Persistence.Migrations
                     b.ToTable("po_lines", (string)null);
                 });
 
+            modelBuilder.Entity("ERPCore.Domain.Entities.ProductConfig", b =>
+                {
+                    b.Property<int>("ConfigId")
+                        .HasColumnType("integer");
+
+                    b.Property<bool>("BrandsEnabled")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("boolean")
+                        .HasDefaultValue(true);
+
+                    b.Property<bool>("ItemTypesEnabled")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("boolean")
+                        .HasDefaultValue(true);
+
+                    b.Property<uint>("RowVersion")
+                        .IsConcurrencyToken()
+                        .ValueGeneratedOnAddOrUpdate()
+                        .HasColumnType("xid")
+                        .HasColumnName("xmin");
+
+                    b.Property<bool>("SubcategoriesEnabled")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("boolean")
+                        .HasDefaultValue(true);
+
+                    b.Property<DateTime?>("UpdatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<int?>("UpdatedBy")
+                        .HasColumnType("integer");
+
+                    b.HasKey("ConfigId");
+
+                    b.HasIndex("UpdatedBy");
+
+                    b.ToTable("product_config", null, t =>
+                        {
+                            t.HasCheckConstraint("ck_product_config_singleton", "\"ConfigId\" = 1");
+                        });
+                });
+
             modelBuilder.Entity("ERPCore.Domain.Entities.PurchaseOrder", b =>
                 {
                     b.Property<int>("PoId")
@@ -1239,6 +1394,51 @@ namespace ERPCore.Infra.Persistence.Migrations
                     b.ToTable("stock_transfer_lines", (string)null);
                 });
 
+            modelBuilder.Entity("ERPCore.Domain.Entities.SubCategory", b =>
+                {
+                    b.Property<int>("SubCategoryId")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("SubCategoryId"));
+
+                    b.Property<int>("CategoryId")
+                        .HasColumnType("integer");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("Name")
+                        .IsRequired()
+                        .HasMaxLength(200)
+                        .HasColumnType("character varying(200)");
+
+                    b.Property<uint>("RowVersion")
+                        .IsConcurrencyToken()
+                        .ValueGeneratedOnAddOrUpdate()
+                        .HasColumnType("xid")
+                        .HasColumnName("xmin");
+
+                    b.Property<string>("Status")
+                        .IsRequired()
+                        .ValueGeneratedOnAdd()
+                        .HasMaxLength(20)
+                        .HasColumnType("character varying(20)")
+                        .HasDefaultValue("Active");
+
+                    b.Property<DateTime?>("UpdatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.HasKey("SubCategoryId");
+
+                    b.HasIndex("Status");
+
+                    b.HasIndex("CategoryId", "Name")
+                        .IsUnique();
+
+                    b.ToTable("subcategories", (string)null);
+                });
+
             modelBuilder.Entity("ERPCore.Domain.Entities.Uom", b =>
                 {
                     b.Property<int>("UomId")
@@ -1516,16 +1716,6 @@ namespace ERPCore.Infra.Persistence.Migrations
                     b.Navigation("Warehouse");
                 });
 
-            modelBuilder.Entity("ERPCore.Domain.Entities.Category", b =>
-                {
-                    b.HasOne("ERPCore.Domain.Entities.Category", "Parent")
-                        .WithMany("Children")
-                        .HasForeignKey("ParentId")
-                        .OnDelete(DeleteBehavior.Restrict);
-
-                    b.Navigation("Parent");
-                });
-
             modelBuilder.Entity("ERPCore.Domain.Entities.Grn", b =>
                 {
                     b.HasOne("ERPCore.Domain.Entities.User", "Creator")
@@ -1616,6 +1806,11 @@ namespace ERPCore.Infra.Persistence.Migrations
                         .OnDelete(DeleteBehavior.Restrict)
                         .IsRequired();
 
+                    b.HasOne("ERPCore.Domain.Entities.Brand", "Brand")
+                        .WithMany()
+                        .HasForeignKey("BrandId")
+                        .OnDelete(DeleteBehavior.Restrict);
+
                     b.HasOne("ERPCore.Domain.Entities.Category", "Category")
                         .WithMany()
                         .HasForeignKey("CategoryId")
@@ -1627,11 +1822,20 @@ namespace ERPCore.Infra.Persistence.Migrations
                         .HasForeignKey("DefaultVendorId")
                         .OnDelete(DeleteBehavior.Restrict);
 
+                    b.HasOne("ERPCore.Domain.Entities.SubCategory", "SubCategory")
+                        .WithMany()
+                        .HasForeignKey("SubCategoryId")
+                        .OnDelete(DeleteBehavior.Restrict);
+
                     b.Navigation("BaseUom");
 
+                    b.Navigation("Brand");
+
                     b.Navigation("Category");
 
                     b.Navigation("DefaultVendor");
+
+                    b.Navigation("SubCategory");
                 });
 
             modelBuilder.Entity("ERPCore.Domain.Entities.ItemReorder", b =>
@@ -1688,6 +1892,16 @@ namespace ERPCore.Infra.Persistence.Migrations
                     b.Navigation("Warehouse");
                 });
 
+            modelBuilder.Entity("ERPCore.Domain.Entities.ProductConfig", b =>
+                {
+                    b.HasOne("ERPCore.Domain.Entities.User", "UpdatedByUser")
+                        .WithMany()
+                        .HasForeignKey("UpdatedBy")
+                        .OnDelete(DeleteBehavior.Restrict);
+
+                    b.Navigation("UpdatedByUser");
+                });
+
             modelBuilder.Entity("ERPCore.Domain.Entities.PurchaseOrder", b =>
                 {
                     b.HasOne("ERPCore.Domain.Entities.User", "Creator")
@@ -2092,6 +2306,17 @@ namespace ERPCore.Infra.Persistence.Migrations
                     b.Navigation("Transfer");
                 });
 
+            modelBuilder.Entity("ERPCore.Domain.Entities.SubCategory", b =>
+                {
+                    b.HasOne("ERPCore.Domain.Entities.Category", "Category")
+                        .WithMany("SubCategories")
+                        .HasForeignKey("CategoryId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("Category");
+                });
+
             modelBuilder.Entity("ERPCore.Domain.Entities.UomConversion", b =>
                 {
                     b.HasOne("ERPCore.Domain.Entities.Uom", "FromUom")
@@ -2159,7 +2384,7 @@ namespace ERPCore.Infra.Persistence.Migrations
 
             modelBuilder.Entity("ERPCore.Domain.Entities.Category", b =>
                 {
-                    b.Navigation("Children");
+                    b.Navigation("SubCategories");
                 });
 
             modelBuilder.Entity("ERPCore.Domain.Entities.Grn", b =>

Backend/ERPCore/Program.cs

@@ -62,6 +62,9 @@ builder.Services.AddScoped(typeof(IRepository<>), typeof(Repository<>));
 builder.Services.AddScoped<IItemService, ItemService>();
 builder.Services.AddScoped<IUomService, UomService>();
 builder.Services.AddScoped<ICategoryService, CategoryService>();
+builder.Services.AddScoped<IBrandService, BrandService>();
+builder.Services.AddScoped<IItemTypeService, ItemTypeService>();
+builder.Services.AddScoped<IProductConfigService, ProductConfigService>();
 builder.Services.AddScoped<IVendorService, VendorService>();
 builder.Services.AddScoped<IWarehouseService, WarehouseService>();
 

Backend/ERPCore/Services/BrandService.cs

@@ -0,0 +1,114 @@
+using ERPCore.Common.Http;
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Brands;
+using ERPCore.Dtos.Common;
+using ERPCore.Infra.UoW;
+using ERPCore.Repositories.Interfaces;
+using ERPCore.Services.Interfaces;
+using ERPCore.System.Errors;
+using Microsoft.EntityFrameworkCore;
+
+namespace ERPCore.Services;
+
+/// <summary>
+/// Brand master service (FR-MD-09). Enforces name uniqueness and optimistic concurrency
+/// per docs/11-BACKEND-PHASE1.md §2.6.
+/// </summary>
+public sealed class BrandService : IBrandService
+{
+    private readonly IRepository<Brand> _brands;
+    private readonly IUnitOfWork _uow;
+
+    public BrandService(IRepository<Brand> brands, IUnitOfWork uow)
+    {
+        _brands = brands;
+        _uow = uow;
+    }
+
+    public async Task<PagedResponse<BrandDto>> ListAsync(PageQuery query, EntityStatus? status, CancellationToken ct = default)
+    {
+        var q = _brands.Query().AsNoTracking();
+        if (!string.IsNullOrWhiteSpace(query.Q))
+        {
+            var term = query.Q.Trim();
+            q = q.Where(b => EF.Functions.ILike(b.Name, $"%{term}%"));
+        }
+        if (status is not null) q = q.Where(b => b.Status == status);
+
+        var total = await q.CountAsync(ct);
+        var rows = await q.OrderBy(b => b.Name)
+            .Skip(query.Skip).Take(query.PageSize)
+            .Select(b => new BrandDto(b.BrandId, b.Name, b.Status, b.CreatedAt, b.UpdatedAt))
+            .ToListAsync(ct);
+
+        return PagedResponse<BrandDto>.Create(rows, query.Page, query.PageSize, total);
+    }
+
+    public async Task<ETagged<BrandDto>?> GetAsync(int brandId, CancellationToken ct = default)
+    {
+        var brand = await _brands.Query().AsNoTracking()
+            .FirstOrDefaultAsync(b => b.BrandId == brandId, ct);
+        return brand is null ? null : new ETagged<BrandDto>(Map(brand), brand.RowVersion);
+    }
+
+    public async Task<ETagged<BrandDto>> CreateAsync(CreateBrandRequest request, CancellationToken ct = default)
+    {
+        var name = request.Name.Trim();
+        if (await _brands.Query().AnyAsync(b => b.Name.ToLower() == name.ToLower(), ct))
+            throw new ConflictException($"A brand named '{name}' already exists.");
+
+        var brand = new Brand
+        {
+            Name = name,
+            Status = EntityStatus.Active,
+            CreatedAt = DateTime.UtcNow
+        };
+
+        await _brands.AddAsync(brand, ct);
+        await _uow.SaveChangesAsync(ct);
+
+        return new ETagged<BrandDto>(Map(brand), brand.RowVersion);
+    }
+
+    public async Task<ETagged<BrandDto>> UpdateAsync(
+        int brandId, UpdateBrandRequest request, uint expectedRowVersion, CancellationToken ct = default)
+    {
+        var brand = await _brands.GetByIdAsync(brandId, ct)
+            ?? throw new NotFoundException($"Brand {brandId} was not found.");
+
+        if (brand.RowVersion != expectedRowVersion)
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, "The brand was modified by another request.", 412);
+
+        var name = request.Name.Trim();
+        if (!string.Equals(brand.Name, name, StringComparison.Ordinal)
+            && await _brands.Query().AnyAsync(b => b.Name.ToLower() == name.ToLower() && b.BrandId != brandId, ct))
+            throw new ConflictException($"A brand named '{name}' already exists.");
+
+        brand.Name = name;
+        brand.UpdatedAt = DateTime.UtcNow;
+
+        try
+        {
+            await _uow.SaveChangesAsync(ct);
+        }
+        catch (DbUpdateConcurrencyException)
+        {
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, "The brand was modified by another request.", 412);
+        }
+
+        return new ETagged<BrandDto>(Map(brand), brand.RowVersion);
+    }
+
+    public async Task SetStatusAsync(int brandId, EntityStatus status, CancellationToken ct = default)
+    {
+        var brand = await _brands.GetByIdAsync(brandId, ct)
+            ?? throw new NotFoundException($"Brand {brandId} was not found.");
+
+        brand.Status = status;
+        brand.UpdatedAt = DateTime.UtcNow;
+        await _uow.SaveChangesAsync(ct);
+    }
+
+    private static BrandDto Map(Brand b) => new(b.BrandId, b.Name, b.Status, b.CreatedAt, b.UpdatedAt);
+}

Backend/ERPCore/Services/CategoryService.cs

@@ -1,4 +1,6 @@
+using ERPCore.Common.Http;
 using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
 using ERPCore.Dtos.Categories;
 using ERPCore.Dtos.Common;
 using ERPCore.Infra.UoW;
@@ -9,18 +11,31 @@ using Microsoft.EntityFrameworkCore;
 
 namespace ERPCore.Services;
 
+/// <summary>
+/// Category + subcategory master service (FR-MD-04). The hierarchy is exactly two levels:
+/// categories no longer self-nest, so there is no cycle to detect and no tree to build
+/// (docs/11-BACKEND-PHASE1.md §2.3).
+/// </summary>
 public sealed class CategoryService : ICategoryService
 {
     private readonly IRepository<Category> _categories;
+    private readonly IRepository<SubCategory> _subCategories;
     private readonly IUnitOfWork _uow;
 
-    public CategoryService(IRepository<Category> categories, IUnitOfWork uow)
+    public CategoryService(
+        IRepository<Category> categories,
+        IRepository<SubCategory> subCategories,
+        IUnitOfWork uow)
     {
         _categories = categories;
+        _subCategories = subCategories;
         _uow = uow;
     }
 
-    public async Task<PagedResponse<CategoryDto>> ListAsync(PageQuery query, CancellationToken ct = default)
+    // Categories ---------------------------------------------------------------
+
+    public async Task<PagedResponse<CategoryDto>> ListAsync(
+        PageQuery query, EntityStatus? status, CancellationToken ct = default)
     {
         var q = _categories.Query().AsNoTracking();
         if (!string.IsNullOrWhiteSpace(query.Q))
@@ -28,43 +43,186 @@ public sealed class CategoryService : ICategoryService
             var term = query.Q.Trim();
             q = q.Where(c => EF.Functions.ILike(c.Name, $"%{term}%"));
         }
+        if (status is not null) q = q.Where(c => c.Status == status);
 
         var total = await q.CountAsync(ct);
         var rows = await q.OrderBy(c => c.Name)
             .Skip(query.Skip).Take(query.PageSize)
-            .Select(c => new CategoryDto(c.CategoryId, c.Name, c.ParentId))
+            .Select(c => new CategoryDto(c.CategoryId, c.Name, c.Status, c.CreatedAt, c.UpdatedAt))
             .ToListAsync(ct);
 
         return PagedResponse<CategoryDto>.Create(rows, query.Page, query.PageSize, total);
     }
 
-    public async Task<IReadOnlyList<CategoryTreeDto>> GetTreeAsync(CancellationToken ct = default)
+    public async Task<ETagged<CategoryDto>?> GetAsync(int categoryId, CancellationToken ct = default)
     {
-        var all = await _categories.Query().AsNoTracking()
-            .OrderBy(c => c.Name)
-            .Select(c => new CategoryDto(c.CategoryId, c.Name, c.ParentId))
-            .ToListAsync(ct);
-
-        var byParent = all.ToLookup(c => c.ParentId);
-
-        List<CategoryTreeDto> Build(int? parentId) =>
-            byParent[parentId]
-                .Select(c => new CategoryTreeDto(c.CategoryId, c.Name, c.ParentId, Build(c.CategoryId)))
-                .ToList();
-
-        return Build(null);
+        var category = await _categories.Query().AsNoTracking()
+            .FirstOrDefaultAsync(c => c.CategoryId == categoryId, ct);
+        return category is null ? null : new ETagged<CategoryDto>(Map(category), category.RowVersion);
     }
 
-    public async Task<CategoryDto> CreateAsync(CreateCategoryRequest request, CancellationToken ct = default)
+    public async Task<ETagged<CategoryDto>> CreateAsync(CreateCategoryRequest request, CancellationToken ct = default)
     {
-        if (request.ParentId is not null
-            && !await _categories.Query().AnyAsync(c => c.CategoryId == request.ParentId, ct))
-            throw new DomainException(ErrorCodes.Validation, $"Parent category {request.ParentId} does not exist.", 422);
+        var name = request.Name.Trim();
+        if (await _categories.Query().AnyAsync(c => c.Name.ToLower() == name.ToLower(), ct))
+            throw new ConflictException($"A category named '{name}' already exists.");
+
+        var category = new Category
+        {
+            Name = name,
+            Status = EntityStatus.Active,
+            CreatedAt = DateTime.UtcNow
+        };
 
-        var category = new Category { Name = request.Name.Trim(), ParentId = request.ParentId };
         await _categories.AddAsync(category, ct);
         await _uow.SaveChangesAsync(ct);
 
-        return new CategoryDto(category.CategoryId, category.Name, category.ParentId);
+        return new ETagged<CategoryDto>(Map(category), category.RowVersion);
     }
+
+    public async Task<ETagged<CategoryDto>> UpdateAsync(
+        int categoryId, UpdateCategoryRequest request, uint expectedRowVersion, CancellationToken ct = default)
+    {
+        var category = await _categories.GetByIdAsync(categoryId, ct)
+            ?? throw new NotFoundException($"Category {categoryId} was not found.");
+
+        if (category.RowVersion != expectedRowVersion)
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, "The category was modified by another request.", 412);
+
+        var name = request.Name.Trim();
+        if (!string.Equals(category.Name, name, StringComparison.Ordinal)
+            && await _categories.Query().AnyAsync(c => c.Name.ToLower() == name.ToLower() && c.CategoryId != categoryId, ct))
+            throw new ConflictException($"A category named '{name}' already exists.");
+
+        category.Name = name;
+        category.UpdatedAt = DateTime.UtcNow;
+
+        await SaveGuardingConcurrencyAsync("category", ct);
+        return new ETagged<CategoryDto>(Map(category), category.RowVersion);
+    }
+
+    public async Task SetStatusAsync(int categoryId, EntityStatus status, CancellationToken ct = default)
+    {
+        var category = await _categories.GetByIdAsync(categoryId, ct)
+            ?? throw new NotFoundException($"Category {categoryId} was not found.");
+
+        category.Status = status;
+        category.UpdatedAt = DateTime.UtcNow;
+        await _uow.SaveChangesAsync(ct);
+    }
+
+    // Subcategories ------------------------------------------------------------
+
+    public async Task<PagedResponse<SubCategoryDto>> ListSubCategoriesAsync(
+        int categoryId, PageQuery query, EntityStatus? status, CancellationToken ct = default)
+    {
+        if (!await _categories.Query().AnyAsync(c => c.CategoryId == categoryId, ct))
+            throw new NotFoundException($"Category {categoryId} was not found.");
+
+        var q = _subCategories.Query().AsNoTracking().Where(s => s.CategoryId == categoryId);
+        if (!string.IsNullOrWhiteSpace(query.Q))
+        {
+            var term = query.Q.Trim();
+            q = q.Where(s => EF.Functions.ILike(s.Name, $"%{term}%"));
+        }
+        if (status is not null) q = q.Where(s => s.Status == status);
+
+        var total = await q.CountAsync(ct);
+        var rows = await q.OrderBy(s => s.Name)
+            .Skip(query.Skip).Take(query.PageSize)
+            .Select(s => new SubCategoryDto(
+                s.SubCategoryId, s.CategoryId, s.Name, s.Status, s.CreatedAt, s.UpdatedAt))
+            .ToListAsync(ct);
+
+        return PagedResponse<SubCategoryDto>.Create(rows, query.Page, query.PageSize, total);
+    }
+
+    public async Task<ETagged<SubCategoryDto>?> GetSubCategoryAsync(int subCategoryId, CancellationToken ct = default)
+    {
+        var sub = await _subCategories.Query().AsNoTracking()
+            .FirstOrDefaultAsync(s => s.SubCategoryId == subCategoryId, ct);
+        return sub is null ? null : new ETagged<SubCategoryDto>(MapSub(sub), sub.RowVersion);
+    }
+
+    public async Task<ETagged<SubCategoryDto>> CreateSubCategoryAsync(
+        int categoryId, CreateSubCategoryRequest request, CancellationToken ct = default)
+    {
+        var category = await _categories.Query().AsNoTracking()
+            .FirstOrDefaultAsync(c => c.CategoryId == categoryId, ct)
+            ?? throw new NotFoundException($"Category {categoryId} was not found.");
+
+        if (category.Status != EntityStatus.Active)
+            throw new DomainException(ErrorCodes.Validation, $"Category {categoryId} is inactive.", 422);
+
+        var name = request.Name.Trim();
+        if (await _subCategories.Query().AnyAsync(
+                s => s.CategoryId == categoryId && s.Name.ToLower() == name.ToLower(), ct))
+            throw new ConflictException($"A subcategory named '{name}' already exists under category {categoryId}.");
+
+        var sub = new SubCategory
+        {
+            CategoryId = categoryId,
+            Name = name,
+            Status = EntityStatus.Active,
+            CreatedAt = DateTime.UtcNow
+        };
+
+        await _subCategories.AddAsync(sub, ct);
+        await _uow.SaveChangesAsync(ct);
+
+        return new ETagged<SubCategoryDto>(MapSub(sub), sub.RowVersion);
+    }
+
+    public async Task<ETagged<SubCategoryDto>> UpdateSubCategoryAsync(
+        int subCategoryId, UpdateSubCategoryRequest request, uint expectedRowVersion, CancellationToken ct = default)
+    {
+        var sub = await _subCategories.GetByIdAsync(subCategoryId, ct)
+            ?? throw new NotFoundException($"Subcategory {subCategoryId} was not found.");
+
+        if (sub.RowVersion != expectedRowVersion)
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, "The subcategory was modified by another request.", 412);
+
+        var name = request.Name.Trim();
+        if (!string.Equals(sub.Name, name, StringComparison.Ordinal)
+            && await _subCategories.Query().AnyAsync(
+                s => s.CategoryId == sub.CategoryId && s.Name.ToLower() == name.ToLower() && s.SubCategoryId != subCategoryId, ct))
+            throw new ConflictException($"A subcategory named '{name}' already exists under category {sub.CategoryId}.");
+
+        // Name only — reparenting is not offered, since it would silently invalidate the
+        // category of every item pointing at this subcategory.
+        sub.Name = name;
+        sub.UpdatedAt = DateTime.UtcNow;
+
+        await SaveGuardingConcurrencyAsync("subcategory", ct);
+        return new ETagged<SubCategoryDto>(MapSub(sub), sub.RowVersion);
+    }
+
+    public async Task SetSubCategoryStatusAsync(int subCategoryId, EntityStatus status, CancellationToken ct = default)
+    {
+        var sub = await _subCategories.GetByIdAsync(subCategoryId, ct)
+            ?? throw new NotFoundException($"Subcategory {subCategoryId} was not found.");
+
+        sub.Status = status;
+        sub.UpdatedAt = DateTime.UtcNow;
+        await _uow.SaveChangesAsync(ct);
+    }
+
+    // ---------------------------------------------------------------------------
+
+    private async Task SaveGuardingConcurrencyAsync(string label, CancellationToken ct)
+    {
+        try
+        {
+            await _uow.SaveChangesAsync(ct);
+        }
+        catch (DbUpdateConcurrencyException)
+        {
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, $"The {label} was modified by another request.", 412);
+        }
+    }
+
+    private static CategoryDto Map(Category c) => new(c.CategoryId, c.Name, c.Status, c.CreatedAt, c.UpdatedAt);
+
+    private static SubCategoryDto MapSub(SubCategory s) => new(
+        s.SubCategoryId, s.CategoryId, s.Name, s.Status, s.CreatedAt, s.UpdatedAt);
 }

Backend/ERPCore/Services/Interfaces/IBrandService.cs

@@ -0,0 +1,16 @@
+using ERPCore.Common.Http;
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Brands;
+using ERPCore.Dtos.Common;
+
+namespace ERPCore.Services.Interfaces;
+
+/// <summary>Brand master business logic (docs/11-BACKEND-PHASE1.md §2.6).</summary>
+public interface IBrandService
+{
+    Task<PagedResponse<BrandDto>> ListAsync(PageQuery query, EntityStatus? status, CancellationToken ct = default);
+    Task<ETagged<BrandDto>?> GetAsync(int brandId, CancellationToken ct = default);
+    Task<ETagged<BrandDto>> CreateAsync(CreateBrandRequest request, CancellationToken ct = default);
+    Task<ETagged<BrandDto>> UpdateAsync(int brandId, UpdateBrandRequest request, uint expectedRowVersion, CancellationToken ct = default);
+    Task SetStatusAsync(int brandId, EntityStatus status, CancellationToken ct = default);
+}

Backend/ERPCore/Services/Interfaces/ICategoryService.cs

@@ -1,12 +1,28 @@
+using ERPCore.Common.Http;
+using ERPCore.Domain.Enums;
 using ERPCore.Dtos.Categories;
 using ERPCore.Dtos.Common;
 
 namespace ERPCore.Services.Interfaces;
 
-/// <summary>Category master business logic (docs/11-BACKEND-PHASE1.md §2.3).</summary>
+/// <summary>
+/// Category + subcategory master business logic (docs/11-BACKEND-PHASE1.md §2.3).
+/// The hierarchy is exactly two levels deep; there is no tree endpoint any more.
+/// </summary>
 public interface ICategoryService
 {
-    Task<PagedResponse<CategoryDto>> ListAsync(PageQuery query, CancellationToken ct = default);
-    Task<IReadOnlyList<CategoryTreeDto>> GetTreeAsync(CancellationToken ct = default);
-    Task<CategoryDto> CreateAsync(CreateCategoryRequest request, CancellationToken ct = default);
+    Task<PagedResponse<CategoryDto>> ListAsync(PageQuery query, EntityStatus? status, CancellationToken ct = default);
+    Task<ETagged<CategoryDto>?> GetAsync(int categoryId, CancellationToken ct = default);
+    Task<ETagged<CategoryDto>> CreateAsync(CreateCategoryRequest request, CancellationToken ct = default);
+    Task<ETagged<CategoryDto>> UpdateAsync(int categoryId, UpdateCategoryRequest request, uint expectedRowVersion, CancellationToken ct = default);
+    Task SetStatusAsync(int categoryId, EntityStatus status, CancellationToken ct = default);
+
+    /// <summary>Subcategories of one category. 404s when the category itself does not exist.</summary>
+    Task<PagedResponse<SubCategoryDto>> ListSubCategoriesAsync(
+        int categoryId, PageQuery query, EntityStatus? status, CancellationToken ct = default);
+
+    Task<ETagged<SubCategoryDto>?> GetSubCategoryAsync(int subCategoryId, CancellationToken ct = default);
+    Task<ETagged<SubCategoryDto>> CreateSubCategoryAsync(int categoryId, CreateSubCategoryRequest request, CancellationToken ct = default);
+    Task<ETagged<SubCategoryDto>> UpdateSubCategoryAsync(int subCategoryId, UpdateSubCategoryRequest request, uint expectedRowVersion, CancellationToken ct = default);
+    Task SetSubCategoryStatusAsync(int subCategoryId, EntityStatus status, CancellationToken ct = default);
 }

Backend/ERPCore/Services/Interfaces/IItemService.cs

@@ -12,7 +12,8 @@ namespace ERPCore.Services.Interfaces;
 public interface IItemService
 {
     Task<PagedResponse<ItemListItemDto>> ListAsync(
-        PageQuery query, EntityStatus? status, int? categoryId, TrackingMode? trackingMode, CancellationToken ct = default);
+        PageQuery query, EntityStatus? status, int? categoryId, int? subCategoryId, int? brandId,
+        TrackingMode? trackingMode, CancellationToken ct = default);
 
     Task<ETagged<ItemDetailDto>?> GetAsync(int itemId, CancellationToken ct = default);
 

Backend/ERPCore/Services/Interfaces/IItemTypeService.cs

@@ -0,0 +1,20 @@
+using ERPCore.Common.Http;
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.ItemTypes;
+
+namespace ERPCore.Services.Interfaces;
+
+/// <summary>
+/// Item type master business logic (docs/11-BACKEND-PHASE1.md §2.7). Plain CRUD over an
+/// unlinked list — no item ever references an item type (docs/10 Part C.9), so there is
+/// nothing here beyond maintaining the names the builder's dropdown reads.
+/// </summary>
+public interface IItemTypeService
+{
+    Task<PagedResponse<ItemTypeDto>> ListAsync(PageQuery query, EntityStatus? status, CancellationToken ct = default);
+    Task<ETagged<ItemTypeDto>?> GetAsync(int itemTypeId, CancellationToken ct = default);
+    Task<ETagged<ItemTypeDto>> CreateAsync(CreateItemTypeRequest request, CancellationToken ct = default);
+    Task<ETagged<ItemTypeDto>> UpdateAsync(int itemTypeId, UpdateItemTypeRequest request, uint expectedRowVersion, CancellationToken ct = default);
+    Task SetStatusAsync(int itemTypeId, EntityStatus status, CancellationToken ct = default);
+}

Backend/ERPCore/Services/Interfaces/IProductConfigService.cs

@@ -0,0 +1,13 @@
+using ERPCore.Common.Http;
+using ERPCore.Dtos.Config;
+
+namespace ERPCore.Services.Interfaces;
+
+/// <summary>Product configuration business logic (docs/11-BACKEND-PHASE1.md §2.8). Singleton.</summary>
+public interface IProductConfigService
+{
+    Task<ETagged<ProductConfigDto>> GetAsync(CancellationToken ct = default);
+
+    Task<ETagged<ProductConfigDto>> UpdateAsync(
+        UpdateProductConfigRequest request, uint expectedRowVersion, CancellationToken ct = default);
+}

Backend/ERPCore/Services/ItemService.cs

@@ -13,36 +13,52 @@ namespace ERPCore.Services;
 
 /// <summary>
 /// Item master service. Enforces SKU uniqueness (SKU_DUPLICATE), reference
-/// integrity, and optimistic concurrency (CONCURRENCY_CONFLICT) per
-/// docs/11-BACKEND-PHASE1.md §2.1–2.2 and 02-SECURITY C.1.
+/// integrity, product-configuration gating (CONFIG_DISABLED), and optimistic
+/// concurrency (CONCURRENCY_CONFLICT) per docs/11-BACKEND-PHASE1.md §2.1–2.2
+/// and 02-SECURITY C.1.
+/// <para>
+/// The SKU arrives generated by the client (it encodes the chosen item-type values,
+/// e.g. "BL-100-0003"); this service only checks that it is unique. Items hold no
+/// item-type reference at all — see docs/10 Part C.9.
+/// </para>
 /// </summary>
 public sealed class ItemService : IItemService
 {
     private readonly IRepository<Item> _items;
     private readonly IRepository<Category> _categories;
+    private readonly IRepository<SubCategory> _subCategories;
+    private readonly IRepository<Brand> _brands;
     private readonly IRepository<Uom> _uoms;
     private readonly IRepository<Vendor> _vendors;
     private readonly IRepository<Warehouse> _warehouses;
+    private readonly IProductConfigService _config;
     private readonly IUnitOfWork _uow;
 
     public ItemService(
         IRepository<Item> items,
         IRepository<Category> categories,
+        IRepository<SubCategory> subCategories,
+        IRepository<Brand> brands,
         IRepository<Uom> uoms,
         IRepository<Vendor> vendors,
         IRepository<Warehouse> warehouses,
+        IProductConfigService config,
         IUnitOfWork uow)
     {
         _items = items;
         _categories = categories;
+        _subCategories = subCategories;
+        _brands = brands;
         _uoms = uoms;
         _vendors = vendors;
         _warehouses = warehouses;
+        _config = config;
         _uow = uow;
     }
 
     public async Task<PagedResponse<ItemListItemDto>> ListAsync(
-        PageQuery query, EntityStatus? status, int? categoryId, TrackingMode? trackingMode, CancellationToken ct = default)
+        PageQuery query, EntityStatus? status, int? categoryId, int? subCategoryId, int? brandId,
+        TrackingMode? trackingMode, CancellationToken ct = default)
     {
         var q = _items.Query().AsNoTracking();
 
@@ -53,14 +69,17 @@ public sealed class ItemService : IItemService
         }
         if (status is not null) q = q.Where(i => i.Status == status);
         if (categoryId is not null) q = q.Where(i => i.CategoryId == categoryId);
+        if (subCategoryId is not null) q = q.Where(i => i.SubCategoryId == subCategoryId);
+        if (brandId is not null) q = q.Where(i => i.BrandId == brandId);
         if (trackingMode is not null) q = q.Where(i => i.TrackingMode == trackingMode);
 
         var total = await q.CountAsync(ct);
         var rows = await q.OrderBy(i => i.Sku)
             .Skip(query.Skip).Take(query.PageSize)
             .Select(i => new ItemListItemDto(
-                i.ItemId, i.Sku, i.Name, i.CategoryId, i.BaseUomId, i.DefaultVendorId,
-                i.ItemType, i.TrackingMode, i.TaxClass, i.Status))
+                i.ItemId, i.Sku, i.Name, i.CategoryId, i.SubCategoryId, i.BrandId,
+                i.BaseUomId, i.DefaultVendorId,
+                i.StockNature, i.TrackingMode, i.TaxClass, i.Status))
             .ToListAsync(ct);
 
         return PagedResponse<ItemListItemDto>.Create(rows, query.Page, query.PageSize, total);
@@ -80,7 +99,9 @@ public sealed class ItemService : IItemService
         if (await _items.Query().AnyAsync(i => i.Sku == request.Sku, ct))
             throw new DomainException(ErrorCodes.SkuDuplicate, $"An item with SKU '{request.Sku}' already exists.", 400);
 
-        await ValidateReferencesAsync(request.CategoryId, request.BaseUomId, request.DefaultVendorId, ct);
+        await ValidateReferencesAsync(
+            request.CategoryId, request.SubCategoryId, request.BrandId,
+            request.BaseUomId, request.DefaultVendorId, ct);
 
         var item = new Item
         {
@@ -88,9 +109,11 @@ public sealed class ItemService : IItemService
             Name = request.Name.Trim(),
             Description = request.Description,
             CategoryId = request.CategoryId,
+            SubCategoryId = request.SubCategoryId,
+            BrandId = request.BrandId,
             BaseUomId = request.BaseUomId,
             DefaultVendorId = request.DefaultVendorId,
-            ItemType = request.ItemType,
+            StockNature = request.StockNature,
             TrackingMode = request.TrackingMode,
             TaxClass = request.TaxClass,
             Status = EntityStatus.Active,
@@ -118,15 +141,19 @@ public sealed class ItemService : IItemService
             && await _items.Query().AnyAsync(i => i.Sku == request.Sku && i.ItemId != itemId, ct))
             throw new DomainException(ErrorCodes.SkuDuplicate, $"An item with SKU '{request.Sku}' already exists.", 400);
 
-        await ValidateReferencesAsync(request.CategoryId, request.BaseUomId, request.DefaultVendorId, ct);
+        await ValidateReferencesAsync(
+            request.CategoryId, request.SubCategoryId, request.BrandId,
+            request.BaseUomId, request.DefaultVendorId, ct);
 
         item.Sku = request.Sku.Trim();
         item.Name = request.Name.Trim();
         item.Description = request.Description;
         item.CategoryId = request.CategoryId;
+        item.SubCategoryId = request.SubCategoryId;
+        item.BrandId = request.BrandId;
         item.BaseUomId = request.BaseUomId;
         item.DefaultVendorId = request.DefaultVendorId;
-        item.ItemType = request.ItemType;
+        item.StockNature = request.StockNature;
         item.TrackingMode = request.TrackingMode;
         item.TaxClass = request.TaxClass;
         item.UpdatedAt = DateTime.UtcNow;
@@ -240,11 +267,56 @@ public sealed class ItemService : IItemService
         return new ItemUomConversionsDto(item.ItemId, item.BaseUomId, conversions);
     }
 
-    private async Task ValidateReferencesAsync(int categoryId, int baseUomId, int? defaultVendorId, CancellationToken ct)
+    /// <summary>
+    /// Validates every FK on an item write, and gates the optional ones on the product
+    /// configuration (FR-MD-11). Note there is no item-type check: nothing on an item
+    /// references an item type, so <c>itemTypesEnabled</c> has nothing to reject here —
+    /// it is advisory and honoured by the frontend only (docs/11 §2.8).
+    /// </summary>
+    private async Task ValidateReferencesAsync(
+        int categoryId, int? subCategoryId, int? brandId, int baseUomId, int? defaultVendorId, CancellationToken ct)
     {
+        var config = (await _config.GetAsync(ct)).Value;
+
         if (!await _categories.Query().AnyAsync(c => c.CategoryId == categoryId, ct))
             throw new DomainException(ErrorCodes.Validation, $"Category {categoryId} does not exist.", 422);
 
+        if (subCategoryId is not null)
+        {
+            if (!config.SubcategoriesEnabled)
+                throw new DomainException(
+                    ErrorCodes.ConfigDisabled,
+                    "Subcategories are disabled in the product configuration; subCategoryId must be null.", 422);
+
+            var sub = await _subCategories.Query().AsNoTracking()
+                .FirstOrDefaultAsync(s => s.SubCategoryId == subCategoryId, ct);
+            if (sub is null)
+                throw new DomainException(ErrorCodes.Validation, $"Subcategory {subCategoryId} does not exist.", 422);
+            if (sub.Status != EntityStatus.Active)
+                throw new DomainException(ErrorCodes.Validation, $"Subcategory {subCategoryId} is inactive.", 422);
+            // The two FKs must agree, or the item would claim a category its subcategory
+            // does not belong to.
+            if (sub.CategoryId != categoryId)
+                throw new DomainException(
+                    ErrorCodes.Validation,
+                    $"Subcategory {subCategoryId} belongs to category {sub.CategoryId}, not {categoryId}.", 422);
+        }
+
+        if (brandId is not null)
+        {
+            if (!config.BrandsEnabled)
+                throw new DomainException(
+                    ErrorCodes.ConfigDisabled,
+                    "Brands are disabled in the product configuration; brandId must be null.", 422);
+
+            var brand = await _brands.Query().AsNoTracking()
+                .FirstOrDefaultAsync(b => b.BrandId == brandId, ct);
+            if (brand is null)
+                throw new DomainException(ErrorCodes.Validation, $"Brand {brandId} does not exist.", 422);
+            if (brand.Status != EntityStatus.Active)
+                throw new DomainException(ErrorCodes.Validation, $"Brand {brandId} is inactive.", 422);
+        }
+
         if (!await _uoms.Query().AnyAsync(u => u.UomId == baseUomId, ct))
             throw new DomainException(ErrorCodes.Validation, $"UOM {baseUomId} does not exist.", 422);
 
@@ -272,8 +344,9 @@ public sealed class ItemService : IItemService
     }
 
     private static ItemDetailDto ToDetail(Item i) => new(
-        i.ItemId, i.Sku, i.Name, i.Description, i.CategoryId, i.BaseUomId, i.DefaultVendorId,
-        i.ItemType, i.TrackingMode, i.TaxClass, i.Status,
+        i.ItemId, i.Sku, i.Name, i.Description, i.CategoryId, i.SubCategoryId, i.BrandId,
+        i.BaseUomId, i.DefaultVendorId,
+        i.StockNature, i.TrackingMode, i.TaxClass, i.Status,
         i.ReorderSettings
             .OrderBy(r => r.WarehouseId)
             .Select(r => new ItemReorderDto(r.WarehouseId, r.ReorderPoint, r.ReorderQty))

Backend/ERPCore/Services/ItemTypeService.cs

@@ -0,0 +1,118 @@
+using ERPCore.Common.Http;
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.ItemTypes;
+using ERPCore.Infra.UoW;
+using ERPCore.Repositories.Interfaces;
+using ERPCore.Services.Interfaces;
+using ERPCore.System.Errors;
+using Microsoft.EntityFrameworkCore;
+
+namespace ERPCore.Services;
+
+/// <summary>
+/// Item type master service (FR-MD-10) — maintains the Color/Size/Material list that
+/// <c>GET /item-types</c> serves to the frontend builder's dropdown. Nothing references
+/// these rows, so there is no in-use check to make and no cascade to worry about
+/// (docs/11-BACKEND-PHASE1.md §2.7, docs/10 Part C.9).
+/// </summary>
+public sealed class ItemTypeService : IItemTypeService
+{
+    private readonly IRepository<ItemType> _itemTypes;
+    private readonly IUnitOfWork _uow;
+
+    public ItemTypeService(IRepository<ItemType> itemTypes, IUnitOfWork uow)
+    {
+        _itemTypes = itemTypes;
+        _uow = uow;
+    }
+
+    public async Task<PagedResponse<ItemTypeDto>> ListAsync(PageQuery query, EntityStatus? status, CancellationToken ct = default)
+    {
+        var q = _itemTypes.Query().AsNoTracking();
+        if (!string.IsNullOrWhiteSpace(query.Q))
+        {
+            var term = query.Q.Trim();
+            q = q.Where(t => EF.Functions.ILike(t.Name, $"%{term}%"));
+        }
+        if (status is not null) q = q.Where(t => t.Status == status);
+
+        var total = await q.CountAsync(ct);
+        var rows = await q.OrderBy(t => t.Name)
+            .Skip(query.Skip).Take(query.PageSize)
+            .Select(t => new ItemTypeDto(t.ItemTypeId, t.Name, t.Status, t.CreatedAt, t.UpdatedAt))
+            .ToListAsync(ct);
+
+        return PagedResponse<ItemTypeDto>.Create(rows, query.Page, query.PageSize, total);
+    }
+
+    public async Task<ETagged<ItemTypeDto>?> GetAsync(int itemTypeId, CancellationToken ct = default)
+    {
+        var itemType = await _itemTypes.Query().AsNoTracking()
+            .FirstOrDefaultAsync(t => t.ItemTypeId == itemTypeId, ct);
+        return itemType is null ? null : new ETagged<ItemTypeDto>(Map(itemType), itemType.RowVersion);
+    }
+
+    public async Task<ETagged<ItemTypeDto>> CreateAsync(CreateItemTypeRequest request, CancellationToken ct = default)
+    {
+        var name = request.Name.Trim();
+        if (await _itemTypes.Query().AnyAsync(t => t.Name.ToLower() == name.ToLower(), ct))
+            throw new ConflictException($"An item type named '{name}' already exists.");
+
+        var itemType = new ItemType
+        {
+            Name = name,
+            Status = EntityStatus.Active,
+            CreatedAt = DateTime.UtcNow
+        };
+
+        await _itemTypes.AddAsync(itemType, ct);
+        await _uow.SaveChangesAsync(ct);
+
+        return new ETagged<ItemTypeDto>(Map(itemType), itemType.RowVersion);
+    }
+
+    public async Task<ETagged<ItemTypeDto>> UpdateAsync(
+        int itemTypeId, UpdateItemTypeRequest request, uint expectedRowVersion, CancellationToken ct = default)
+    {
+        var itemType = await _itemTypes.GetByIdAsync(itemTypeId, ct)
+            ?? throw new NotFoundException($"Item type {itemTypeId} was not found.");
+
+        if (itemType.RowVersion != expectedRowVersion)
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, "The item type was modified by another request.", 412);
+
+        var name = request.Name.Trim();
+        if (!string.Equals(itemType.Name, name, StringComparison.Ordinal)
+            && await _itemTypes.Query().AnyAsync(t => t.Name.ToLower() == name.ToLower() && t.ItemTypeId != itemTypeId, ct))
+            throw new ConflictException($"An item type named '{name}' already exists.");
+
+        // Renaming does not touch existing items: their SKUs already encode the values that
+        // were chosen, and nothing joins back to this row (docs/10 Part C.9).
+        itemType.Name = name;
+        itemType.UpdatedAt = DateTime.UtcNow;
+
+        try
+        {
+            await _uow.SaveChangesAsync(ct);
+        }
+        catch (DbUpdateConcurrencyException)
+        {
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, "The item type was modified by another request.", 412);
+        }
+
+        return new ETagged<ItemTypeDto>(Map(itemType), itemType.RowVersion);
+    }
+
+    public async Task SetStatusAsync(int itemTypeId, EntityStatus status, CancellationToken ct = default)
+    {
+        var itemType = await _itemTypes.GetByIdAsync(itemTypeId, ct)
+            ?? throw new NotFoundException($"Item type {itemTypeId} was not found.");
+
+        itemType.Status = status;
+        itemType.UpdatedAt = DateTime.UtcNow;
+        await _uow.SaveChangesAsync(ct);
+    }
+
+    private static ItemTypeDto Map(ItemType t) => new(t.ItemTypeId, t.Name, t.Status, t.CreatedAt, t.UpdatedAt);
+}

Backend/ERPCore/Services/ProductConfigService.cs

@@ -0,0 +1,71 @@
+using ERPCore.Common.Http;
+using ERPCore.Domain.Entities;
+using ERPCore.Dtos.Config;
+using ERPCore.Infra.Auth;
+using ERPCore.Infra.UoW;
+using ERPCore.Repositories.Interfaces;
+using ERPCore.Services.Interfaces;
+using ERPCore.System.Errors;
+using Microsoft.EntityFrameworkCore;
+
+namespace ERPCore.Services;
+
+/// <summary>
+/// Product configuration service (FR-MD-11) over the singleton row seeded by DataSeeder.
+/// Reads are never gated — only writes consult the flags — so switching a feature off
+/// leaves existing data readable (docs/11-BACKEND-PHASE1.md §2.8).
+/// </summary>
+public sealed class ProductConfigService : IProductConfigService
+{
+    private readonly IRepository<ProductConfig> _config;
+    private readonly ICurrentUser _currentUser;
+    private readonly IUnitOfWork _uow;
+
+    public ProductConfigService(IRepository<ProductConfig> config, ICurrentUser currentUser, IUnitOfWork uow)
+    {
+        _config = config;
+        _currentUser = currentUser;
+        _uow = uow;
+    }
+
+    public async Task<ETagged<ProductConfigDto>> GetAsync(CancellationToken ct = default)
+    {
+        var config = await _config.Query().AsNoTracking()
+            .FirstOrDefaultAsync(c => c.ConfigId == ProductConfig.SingletonId, ct)
+            ?? throw new NotFoundException("Product configuration has not been seeded.");
+
+        return new ETagged<ProductConfigDto>(Map(config), config.RowVersion);
+    }
+
+    public async Task<ETagged<ProductConfigDto>> UpdateAsync(
+        UpdateProductConfigRequest request, uint expectedRowVersion, CancellationToken ct = default)
+    {
+        var config = await _config.GetByIdAsync(ProductConfig.SingletonId, ct)
+            ?? throw new NotFoundException("Product configuration has not been seeded.");
+
+        if (config.RowVersion != expectedRowVersion)
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, "The configuration was modified by another request.", 412);
+
+        // Non-null by [Required] on the nullable bools — an omitted flag is a 400, so the
+        // model binder has already rejected anything that would reach here with a null.
+        config.SubcategoriesEnabled = request.SubcategoriesEnabled!.Value;
+        config.BrandsEnabled = request.BrandsEnabled!.Value;
+        config.ItemTypesEnabled = request.ItemTypesEnabled!.Value;
+        config.UpdatedAt = DateTime.UtcNow;
+        config.UpdatedBy = _currentUser.AuditUserId;
+
+        try
+        {
+            await _uow.SaveChangesAsync(ct);
+        }
+        catch (DbUpdateConcurrencyException)
+        {
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, "The configuration was modified by another request.", 412);
+        }
+
+        return new ETagged<ProductConfigDto>(Map(config), config.RowVersion);
+    }
+
+    private static ProductConfigDto Map(ProductConfig c) => new(
+        c.SubcategoriesEnabled, c.BrandsEnabled, c.ItemTypesEnabled, c.UpdatedAt, c.UpdatedBy);
+}

Backend/ERPCore/System/Errors/ErrorCodes.cs

@@ -24,6 +24,7 @@ public static class ErrorCodes
     public const string ReasonCodeRequired = "REASON_CODE_REQUIRED";
     public const string ConcurrencyConflict = "CONCURRENCY_CONFLICT";
     public const string IdempotencyReplay = "IDEMPOTENCY_REPLAY";
+    public const string ConfigDisabled = "CONFIG_DISABLED";
 
     // Auth proxy (AuthController → AuthHex, docs/11 §2.0)
     public const string AuthUpstreamError = "AUTH_UPSTREAM_ERROR";

Backend/PROGRESS.md

@@ -15,14 +15,41 @@ Convention: `docs/01-DOC-GUIDE.md §6`. Update this file in the **same commit**
 - [x] ProblemDetails middleware + domain exception → `code` mapping (System/Errors; full §7 catalog added to `ErrorCodes`)
 
 ## 1. Master Data
-> Code complete for all items below (2026-07-09). **Live smoke test PASSED against Postgres (2026-07-10):** create/get/list/update/status/reorder/uom-conversions across all 5 controllers; ETag round-trip 200 / stale→412 / missing→428; SKU_DUPLICATE→400; bad reference→422; missing-field→400 ValidationProblemDetails; category `?tree=true` nesting; `pageSize=9999` clamped to 200; deactivate via PATCH status→204. **Flipped `[x]` on 2026-07-14** — the §6 security gate (00-CORE §8: auth control 02-SECURITY B.1 + audit trail B.3) is now met (AuthHex RS256 validation + `[Authorize]` door policy + shadow-user provisioning, and the audit trail). The dated smoke-test notes in §2–§5 that reference a pending "§6 gate" are historical.
-- [x] Item: entity + config + enums (ItemType, TrackingMode; EntityStatus added) — `xmin`/RowVersion concurrency token (Npgsql), unique SKU
+> Code complete for all items below (2026-07-09). **Live smoke test PASSED against Postgres (2026-07-10):** create/get/list/update/status/reorder/uom-conversions across all 5 controllers; ETag round-trip 200 / stale→412 / missing→428; SKU_DUPLICATE→400; bad reference→422; missing-field→400 ValidationProblemDetails; category `?tree=true` nesting (**that endpoint was removed on 2026-07-16** — categories no longer nest; see the entry at the end of this section); `pageSize=9999` clamped to 200; deactivate via PATCH status→204. **Flipped `[x]` on 2026-07-14** — the §6 security gate (00-CORE §8: auth control 02-SECURITY B.1 + audit trail B.3) is now met (AuthHex RS256 validation + `[Authorize]` door policy + shadow-user provisioning, and the audit trail). The dated smoke-test notes in §2–§5 that reference a pending "§6 gate" are historical.
+- [x] Item: entity + config + enums (StockNature [ex-ItemType], TrackingMode; EntityStatus added) — `xmin`/RowVersion concurrency token (Npgsql), unique SKU
 - [x] Item: repository (generic) + service + controller (CRUD, narrow DTOs, ETag/If-Match→412, SKU_DUPLICATE, reference validation) — server-controlled fields excluded (02-SECURITY C.1)
 - [x] UOM + UOM conversions (`GET/POST /uoms`, `PUT /items/{id}/uom-conversions` full-replace upsert)
-- [x] Category (hierarchy, `GET /categories?tree=true` nested build, parent-exists validation)
+- [x] Category — **rebuilt 2026-07-16 as a two-level Category/SubCategory model** (was a self-nesting tree); full CRUD + status + ETag, which it previously lacked entirely
 - [x] Vendor (CRUD, ETag/If-Match, unique code, deactivate via `PATCH /vendors/{id}/status`)
 - [x] Warehouse + Bin (`/warehouses`, nested `/warehouses/{id}/bins`, bin code unique per warehouse)
 - [x] Item reorder settings (`PUT /items/{id}/reorder` full-replace upsert, warehouse-exists validation)
+- [x] Brand master (FR-MD-09) — CRUD + status + ETag; `Item.brandId` nullable FK
+- [x] Item Type master (FR-MD-10) — CRUD + status + ETag; **unreferenced by design**, feeds the builder dropdown only
+- [x] SubCategory (FR-MD-04) — nested list/create under a category, `PUT`/`PATCH status` by id; `Item.subCategoryId` nullable FK, validated to belong to `categoryId`
+- [x] Product Configuration (FR-MD-11) — singleton `GET`/`PUT /product-config`; `CONFIG_DISABLED` gating on item writes
+
+> ### 2026-07-16 — Brands, Subcategories, Item Types, Product Config (migration #2)
+> Makes real three concepts the frontend had been faking on mock data (`Frontend/erp-system/lib/api/mock-data.ts`), per docs/10 §B.3.1 FR-MD-09/10/11 and docs/11 §2.3/2.6/2.7/2.8.
+>
+> **Deviations / decisions (all recorded in docs/10 §B.8.4 #11–13):**
+> - **`ItemType` enum → `StockNature`.** The Stocked/NonStocked/Service enum was renamed to free the name `ItemType` for the new master entity. FR-MD-01 stays satisfied; the DB column was renamed in-place (`RenameColumn`, data preserved). Blast radius was 4 files — nothing in stock/GRN/costing branches on it.
+> - **`CATEGORY.parent_id` removed.** Arbitrary nesting is gone, replaced by a dedicated `SUBCATEGORY` table (exactly two levels). Items now carry **both** FKs; previously the frontend collapsed them (`effectiveCategoryId = subCategoryId ?? categoryId`), losing the parent.
+> - **Item types are unlinked to items, deliberately.** No value table, no join — values live only in the client-generated SKU (`BL-100-0003`) and are never parsed server-side. Accepted trade-off (no query-by-colour/size; renaming a type doesn't touch existing SKUs) written up in docs/10 Part C.9. This is *not* a product-variation model; none was requested.
+> - **`itemTypesEnabled` is advisory, not enforced.** With no item-type reference on an item there is nothing on a write to reject; only `subcategoriesEnabled`/`brandsEnabled` produce `CONFIG_DISABLED`. Stated plainly in docs/11 §2.8 so it isn't mistaken for a backend guarantee.
+> - **`PUT /product-config` is door-policy-gated only** — any ERP-admitted user can flip the flags. A `CONFIG_MANAGE` permission is reserved for when RBAC lands (open decision #13).
+> - **`brandId` is now a documented field**, no longer the undocumented frontend-only extra it was.
+>
+> **Migration #2 (`AddBrandsSubcategoriesItemTypesAndProductConfig`) carries data, not just DDL.** The scaffolded version dropped `parent_id` outright, which would have silently flattened every child category into a root and stranded items on the wrong one. Hand-added: backfill of child categories into `subcategories`, repoint of items onto the correct (category, subcategory) pair, delete of the migrated rows, and the config singleton insert. A recursive CTE maps categories at **any** depth to their root ancestor, since the old model allowed unlimited nesting but the new one is two levels — a grandchild becomes a subcategory of its *root*, not of its (now-nonexistent) parent category. `Down()` was likewise hand-written to restore the tree instead of dropping `subcategories` and losing it.
+>
+> Also fixed while writing it: the `ck_product_config_singleton` check constraint was scaffolded as `config_id = 1`, but the column is created quoted-PascalCase (`"ConfigId"`) — unquoted, Postgres folds it to a column that doesn't exist. And `UpdateProductConfigRequest`'s flags are `bool?` on purpose: `[Required]` on a non-nullable `bool` is a no-op, so a body of `{}` would have bound all three to `false` and silently switched every feature off.
+>
+> **Schema/migration verified:** `dotnet build` clean. Migration `Up` **and** `Down` exercised against a purpose-seeded 3-level tree (Hardware → Fasteners → Bolts, plus items on each level and a childless root) — 9/9 forward assertions and 7/7 rollback assertions passed, including the grandchild depth-collapse and `StockNature` data preservation; the fixture was then removed. `DataSeeder` seeds `Color`/`Size` + the config singleton idempotently (it needed restructuring — an early `return` in the reason-code path would otherwise have skipped the new seeds on every start after the first).
+>
+> **Live smoke test PASSED (2026-07-16), all 24 checks, against Postgres + a real AuthHex session.** Auth note: a token *is* obtainable despite the `loginUser` blocker — **`POST /api/v1/auth/register` succeeds and issues the `erp_at` session cookie directly**, and the JWT handler's cookie fallback means that session authenticates every other controller. (`loginUser` still `500`s "Invalid credentials" for that same freshly-registered user, by username *or* email, with *or* without `userTypeId` — the §6 blocker is real and reproduces, but it is not a barrier to testing.) Registration needs AuthHex-internal `roleId`/`userTypeId` GUIDs, supplied by the user; Admin = role `08de6a11-9e9f-4401-8a10-6859860b41ec` / userType `00000000-0000-0000-0000-000000000004`.
+>
+> Covered: brand/category/subcategory/item-type create; **case-insensitive duplicate name → 409** (brand, and subcategory scoped per-parent); subcategory under a missing category → 404; item create carrying all three new FKs with SKU `BL-100-0003` → 201 and full round-trip on `GET /items/{id}`; new `brandId`/`subCategoryId` list filters; **cross-FK guard → 422** ("Subcategory 3 belongs to category 7, not 8"); missing/inactive brand → 422; `PUT /product-config {}` → **400** (proving the `bool?` fix — an empty body no longer silently disables everything); `subcategoriesEnabled:false` + `subCategoryId` → **422 CONFIG_DISABLED**, same item without it → 201, and **pre-existing items with a subcategory still read back fine**; `brandsEnabled:false` + `brandId` → 422; **`itemTypesEnabled:false` correctly does NOT block item writes** (advisory, as documented); ETag round-trip 200 / stale-but-well-formed → **412 CONCURRENCY_CONFLICT** (brand + subcategory) / absent → 428; `PATCH /status` → 204 then inactive-brand reference → 422; and **renaming an item type left existing SKUs untouched**, confirming the intended decoupling. Audit stamp confirmed live: `product_config.updatedBy` resolved to a JIT-provisioned shadow user (`SMOKE001`) from the AuthHex `UserId`/`NIC` claims.
+>
+> Test data was removed afterwards (masters back to empty, config flags restored to all-true with the audit stamp cleared). **Two artifacts left behind on purpose:** the AuthHex user `smoketest_admin` / NIC `SMOKE001` in AuthHex's own MySQL store, and its ERPCore shadow user (`users.UserId = 3`) — referenced by nothing, kept so the session can be reused for future testing. Delete both if unwanted.
 
 ## 2. Procurement
 > Requisition/RFQ/PO implemented 2026-07-10. **Live smoke test PASSED** (docNo `PR/RFQ/PO-2026-#####` gap-controlled + incrementing, requestedBy/createdBy = seeded system user, RFQ comparison matrix, duplicate quotation→409, PO auto-approve + server-computed totals matching the spec example `112100/20178/132278`, edit-while-open with recomputed totals + ETag 200/412, PO_NOT_EDITABLE→409 on cancelled, cancel→200, bad reference→422). Same `[~]` reason as §1: the §6 security gate (auth + audit) is not yet wired.
@@ -147,3 +174,7 @@ Convention: `docs/01-DOC-GUIDE.md §6`. Update this file in the **same commit**
 - **Live-verified against the running AuthHex instance (`:5011`) and ERPCore (`:5224`, dev):** `register` → `200` with `Set-Cookie: erp_at`(httpOnly/Secure/Strict/maxAge=3600) + `erp_rt`(httpOnly/Secure/Strict/Path=`/api/v1/auth/refresh-token`/30d) + `XSRF-TOKEN`(Secure/Strict, JS-readable), body carries `user`+`expiresIn` only, **no tokens**; the `erp_at` cookie alone (zero `Authorization` header) authenticated `GET /api/v1/items` — confirms the `OnMessageReceived` cookie fallback works for every existing v1 controller unchanged; `GET /api/v1/auth/sessions` (protected, cookie-authenticated) → `200`; mutating `POST /api/v1/auth/change-password` without `X-XSRF-TOKEN` → `403 CSRF_TOKEN_MISMATCH`, with the matching header → `204` + all three cookies cleared, exactly as designed.
 - **Found + fixed a real bug during live testing:** `AuthHexClient` trusted the envelope's `success` flag alone; AuthHex was observed returning **`HTTP 500` with `"success": true, "data": null`** on a business failure (invalid-credentials login), which slipped past the `!envelope.Success` check and null-derefed inside `AuthUserService.ToSessionResult` (`NullReferenceException` → bare unhandled `500`, no `code`). Fixed `AuthHexClient.CallAsync` to also fail on `!httpResponse.IsSuccessStatusCode` regardless of `envelope.Success`, plus added `result is null` guards in `ToSessionResult`/`ToOtpSessionResult`/`AuthAltService.VerifyOtpAsync` as defense-in-depth. Re-verified: the same invalid-credentials case now returns a clean `500 AUTH_UPSTREAM_ERROR` ProblemDetails instead of crashing.
 - **Login/refresh/logout left unverified live** — `loginUser` currently fails with `{"statusCode":500,"success":true,"message":"Invalid credentials","data":null}` on AuthHex **even immediately after a fresh registration with the exact same credentials**, confirmed by calling AuthHex's `/api/user` directly with the identical payload (bypassing ERPCore entirely) — this is a bug in AuthHex's own `loginUser`/password-verification path, not in this proxy. Blocked on an AuthHex-side fix; re-run the register→login→cookie→refresh→logout pass once that's resolved.
+  - **ROOT CAUSE FOUND (2026-07-16), in `ERP_Auth_Service` — two independent bugs, both one-liners. Not fixed here: different project, outside this repo's scope.** Re-confirmed the failure against a user registered this session (`smoketest_admin`/`SMOKE001`), by username *and* email, with *and* without `userTypeId`.
+    1. **The password is never stored.** `Services/UserManager/UserManagerService.cs:97` computes `var PasswordHash = PasswordHasher.Hash(...)`, but the assignment in the `new User { … }` initializer at **line 116 is commented out** (`//PasswordHash = PasswordHash`). Every registered user lands in MySQL with a null `PasswordHash`, so `loginUser`'s `if (string.IsNullOrEmpty(user.PasswordHash) || !PasswordHasher.Verify(...))` (line 230) always throws `"Invalid credentials"`. Uncommenting line 116 should fix login outright. Note existing users are unrecoverable — their hashes were never written — so they need re-registration or a password reset (`ChangeUserPassword`/`UpdateUser` do persist the hash correctly, and `UpdateUser` even handles the null-hash case at line 836).
+    2. **Username is not a valid login identifier.** `Repos/UserManageRepository.cs:46` `GetUserByIdentifierAndType` matches only `Email`/`MobileNumber`/`Nic` — **not `UserName`** — and ignores its `userTypeId` argument entirely (that filtering sits commented out at lines 56–65, so the "AndType" half of the method name is currently a lie). Even with bug 1 fixed, `identifier: "<username>"` will not resolve a user; only email/mobile/NIC will.
+  - **Workaround meanwhile: `POST /api/v1/auth/register` issues a working `erp_at` session cookie directly**, which authenticates every v1 controller via the handler's cookie fallback. That is how this session's Master-Data smoke test (§1) was run — no login needed.