Merge branch 'Dev' into fix/phase-01

- Introduced a new column 'auth_user_id' of type UUID to the 'users' table.
- Updated existing user data to set 'auth_user_id' to null for UserId 1.
- Created a unique index on 'auth_user_id' to enforce uniqueness.
- Implemented rollback functionality to remove the column and index if needed.

Backend/ERPCore/Common/Http/ETag.cs

@@ -0,0 +1,37 @@
+namespace ERPCore.Common.Http;
+
+/// <summary>
+/// Encodes the PostgreSQL xmin concurrency token (a <see cref="uint"/>) as an
+/// opaque, quoted HTTP ETag and parses <c>If-Match</c> values back. Round-trips
+/// via base64 so the value is stable and content-type agnostic
+/// (docs/11-BACKEND-PHASE1.md §1.6).
+/// </summary>
+public static class ETag
+{
+    /// <summary>Quoted ETag string for a row-version token, e.g. <c>"0RsAAA=="</c>.</summary>
+    public static string From(uint rowVersion)
+        => "\"" + Convert.ToBase64String(BitConverter.GetBytes(rowVersion)) + "\"";
+
+    /// <summary>Parse an <c>If-Match</c> header value (quoted, optionally weak) to a token.</summary>
+    public static bool TryParse(string? ifMatch, out uint rowVersion)
+    {
+        rowVersion = 0;
+        if (string.IsNullOrWhiteSpace(ifMatch)) return false;
+
+        var v = ifMatch.Trim();
+        if (v.StartsWith("W/", StringComparison.OrdinalIgnoreCase)) v = v[2..].Trim();
+        v = v.Trim('"');
+
+        try
+        {
+            var bytes = Convert.FromBase64String(v);
+            if (bytes.Length != sizeof(uint)) return false;
+            rowVersion = BitConverter.ToUInt32(bytes);
+            return true;
+        }
+        catch (FormatException)
+        {
+            return false;
+        }
+    }
+}

Backend/ERPCore/Common/Http/ETagged.cs

@@ -0,0 +1,7 @@
+namespace ERPCore.Common.Http;
+
+/// <summary>
+/// Pairs a response DTO with the aggregate's current row-version so the controller
+/// can emit an <c>ETag</c> header without the token leaking into the JSON body.
+/// </summary>
+public sealed record ETagged<T>(T Value, uint RowVersion);

Backend/ERPCore/Controllers/ApiControllerBase.cs

@@ -0,0 +1,32 @@
+using ERPCore.Common.Http;
+using ERPCore.Infra.Auth;
+using ERPCore.System.Errors;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>
+/// Base for the v1 API controllers. Centralises ETag / If-Match handling
+/// (docs/11-BACKEND-PHASE1.md §1.6) so concurrency behaviour is uniform.
+/// Each controller declares its own explicit lowercase <c>[Route]</c> to match
+/// the API contract paths (docs/11 §1.1). Every v1 endpoint requires a valid
+/// AuthHex token satisfying the ERP door policy (docs/10 A.4).
+/// </summary>
+[ApiController]
+[Produces("application/json")]
+[Authorize(JwtAuthExtensions.ErpAccessPolicy)]
+public abstract class ApiControllerBase : ControllerBase
+{
+    /// <summary>Parse a mandatory <c>If-Match</c> header, or 428 if absent/malformed.</summary>
+    protected uint RequireIfMatch()
+    {
+        var header = Request.Headers.IfMatch.ToString();
+        if (!ETag.TryParse(header, out var rowVersion))
+            throw new DomainException("PRECONDITION_REQUIRED", "A valid If-Match header is required for this update.", 428);
+        return rowVersion;
+    }
+
+    /// <summary>Emit the strong <c>ETag</c> response header for a row-version token.</summary>
+    protected void SetETag(uint rowVersion) => Response.Headers.ETag = ETag.From(rowVersion);
+}

Backend/ERPCore/Controllers/AuditLogsController.cs

@@ -0,0 +1,26 @@
+using ERPCore.Dtos.Audit;
+using ERPCore.Dtos.Common;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>
+/// Read-only audit trail (FR-X-02; auditor role). Extends the documented §11 API —
+/// the audit trail is required (AR-01 compensating control) and read access is the
+/// only way to consume it.
+/// </summary>
+[Route("api/v1/audit-logs")]
+public sealed class AuditLogsController : ApiControllerBase
+{
+    private readonly IAuditService _audit;
+
+    public AuditLogsController(IAuditService audit) => _audit = audit;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<AuditLogDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<AuditLogDto>>> List(
+        [FromQuery] string? entityType, [FromQuery] long? entityId, [FromQuery] long? userId,
+        [FromQuery] DateOnly? from, [FromQuery] DateOnly? to, [FromQuery] PageQuery query, CancellationToken ct)
+        => Ok(await _audit.ListLogsAsync(entityType, entityId, userId, from, to, query, ct));
+}

Backend/ERPCore/Controllers/CategoriesController.cs

@@ -0,0 +1,31 @@
+using ERPCore.Dtos.Categories;
+using ERPCore.Dtos.Common;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Category endpoints (docs/11-BACKEND-PHASE1.md §2.3).</summary>
+[Route("api/v1/categories")]
+public sealed class CategoriesController : ApiControllerBase
+{
+    private readonly ICategoryService _categories;
+
+    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));
+
+    [HttpPost]
+    [ProducesResponseType(typeof(CategoryDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    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);
+    }
+}

Backend/ERPCore/Controllers/GrnsController.cs

@@ -0,0 +1,52 @@
+using ERPCore.Dtos.Grn;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Goods-receipt endpoints (docs/11 §4).</summary>
+[Route("api/v1/grns")]
+public sealed class GrnsController : ApiControllerBase
+{
+    private readonly IGrnService _grns;
+
+    public GrnsController(IGrnService grns) => _grns = grns;
+
+    [HttpGet("{grnId:long}")]
+    [ProducesResponseType(typeof(GrnDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<GrnDto>> GetById(long grnId, CancellationToken ct)
+    {
+        var dto = await _grns.GetAsync(grnId, ct);
+        return dto is null ? NotFound() : Ok(dto);
+    }
+
+    /// <summary>Create a Draft GRN against a PO or direct. Cost is PO-derived for PO lines.</summary>
+    [HttpPost]
+    [ProducesResponseType(typeof(GrnDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<GrnDto>> Create([FromBody] CreateGrnRequest request, CancellationToken ct)
+    {
+        var dto = await _grns.CreateAsync(request, ct);
+        return Created($"/api/v1/grns/{dto.GrnId}", dto);
+    }
+
+    /// <summary>Confirm: create FIFO layers + inbound ledger + update PO receipts (single UoW txn).</summary>
+    [HttpPost("{grnId:long}/confirm")]
+    [ProducesResponseType(typeof(GrnConfirmResultDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<GrnConfirmResultDto>> Confirm(
+        long grnId, [FromHeader(Name = "Idempotency-Key")] string? idempotencyKey, CancellationToken ct)
+        => Ok(await _grns.ConfirmAsync(grnId, idempotencyKey, ct));
+
+    /// <summary>Release or reject an inspection-hold line (FR-GRN-05).</summary>
+    [HttpPost("{grnId:long}/lines/{grnLineId:long}/release")]
+    [ProducesResponseType(typeof(ReleaseLineResultDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<ReleaseLineResultDto>> Release(
+        long grnId, long grnLineId, [FromBody] ReleaseLineRequest request, CancellationToken ct)
+        => Ok(await _grns.ReleaseLineAsync(grnId, grnLineId, request.Action, ct));
+}

Backend/ERPCore/Controllers/ItemsController.cs

@@ -0,0 +1,89 @@
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Items;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Item master endpoints (docs/11-BACKEND-PHASE1.md §2.1–2.2).</summary>
+[Route("api/v1/items")]
+public sealed class ItemsController : ApiControllerBase
+{
+    private readonly IItemService _items;
+
+    public ItemsController(IItemService items) => _items = items;
+
+    /// <summary>List items with optional filters and paging.</summary>
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<ItemListItemDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<ItemListItemDto>>> List(
+        [FromQuery] PageQuery query,
+        [FromQuery] EntityStatus? status,
+        [FromQuery] long? categoryId,
+        [FromQuery] TrackingMode? trackingMode,
+        CancellationToken ct)
+        => Ok(await _items.ListAsync(query, status, categoryId, trackingMode, ct));
+
+    /// <summary>Get a single item; returns an <c>ETag</c> for optimistic concurrency.</summary>
+    [HttpGet("{itemId:long}")]
+    [ProducesResponseType(typeof(ItemDetailDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<ItemDetailDto>> GetById(long itemId, CancellationToken ct)
+    {
+        var result = await _items.GetAsync(itemId, ct);
+        if (result is null) return NotFound();
+
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    /// <summary>Create an item (SKU unique). Server sets status and timestamps.</summary>
+    [HttpPost]
+    [ProducesResponseType(typeof(ItemDetailDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<ItemDetailDto>> Create([FromBody] CreateItemRequest request, CancellationToken ct)
+    {
+        var result = await _items.CreateAsync(request, ct);
+        SetETag(result.RowVersion);
+        return Created($"/api/v1/items/{result.Value.ItemId}", result.Value);
+    }
+
+    /// <summary>Full update; requires <c>If-Match</c> (412 on stale ETag).</summary>
+    [HttpPut("{itemId:long}")]
+    [ProducesResponseType(typeof(ItemDetailDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status412PreconditionFailed)]
+    public async Task<ActionResult<ItemDetailDto>> Update(long itemId, [FromBody] UpdateItemRequest request, CancellationToken ct)
+    {
+        var expected = RequireIfMatch();
+        var result = await _items.UpdateAsync(itemId, request, expected, ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    /// <summary>Activate / deactivate the item (FR-MD-08 — deactivate, not delete).</summary>
+    [HttpPatch("{itemId:long}/status")]
+    [ProducesResponseType(StatusCodes.Status204NoContent)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> SetStatus(long itemId, [FromBody] UpdateItemStatusRequest request, CancellationToken ct)
+    {
+        await _items.SetStatusAsync(itemId, request.Status, ct);
+        return NoContent();
+    }
+
+    /// <summary>Replace the item's per-warehouse reorder settings (FR-MD-05).</summary>
+    [HttpPut("{itemId:long}/reorder")]
+    [ProducesResponseType(typeof(ItemReorderSettingsDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<ItemReorderSettingsDto>> UpdateReorder(long itemId, [FromBody] UpdateReorderRequest request, CancellationToken ct)
+        => Ok(await _items.UpdateReorderAsync(itemId, request, ct));
+
+    /// <summary>Replace the item's UOM conversions (FR-MD-02).</summary>
+    [HttpPut("{itemId:long}/uom-conversions")]
+    [ProducesResponseType(typeof(ItemUomConversionsDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<ItemUomConversionsDto>> UpdateUomConversions(long itemId, [FromBody] UpdateUomConversionsRequest request, CancellationToken ct)
+        => Ok(await _items.UpdateUomConversionsAsync(itemId, request, ct));
+}

Backend/ERPCore/Controllers/JournalEntriesController.cs

@@ -0,0 +1,24 @@
+using ERPCore.Dtos.Audit;
+using ERPCore.Dtos.Common;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>
+/// Read-only GL-ready journal stubs (FR-STK-13; consumed by the Accounting phase).
+/// Data only — no posting in Phase 1.
+/// </summary>
+[Route("api/v1/journal-entries")]
+public sealed class JournalEntriesController : ApiControllerBase
+{
+    private readonly IAuditService _audit;
+
+    public JournalEntriesController(IAuditService audit) => _audit = audit;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<JournalEntryStubDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<JournalEntryStubDto>>> List(
+        [FromQuery] string? sourceDocType, [FromQuery] long? sourceDocId, [FromQuery] PageQuery query, CancellationToken ct)
+        => Ok(await _audit.ListJournalAsync(sourceDocType, sourceDocId, query, ct));
+}

Backend/ERPCore/Controllers/PurchaseOrdersController.cs

@@ -0,0 +1,74 @@
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Procurement;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Purchase-order endpoints (docs/11 §3.3).</summary>
+[Route("api/v1/purchase-orders")]
+public sealed class PurchaseOrdersController : ApiControllerBase
+{
+    private readonly IPurchaseOrderService _pos;
+
+    public PurchaseOrdersController(IPurchaseOrderService pos) => _pos = pos;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<PurchaseOrderSummaryDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<PurchaseOrderSummaryDto>>> List(
+        [FromQuery] PageQuery query, [FromQuery] PurchaseOrderStatus? status, [FromQuery] long? vendorId, CancellationToken ct)
+        => Ok(await _pos.ListAsync(query, status, vendorId, ct));
+
+    [HttpGet("{poId:long}")]
+    [ProducesResponseType(typeof(PurchaseOrderDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<PurchaseOrderDto>> GetById(long poId, CancellationToken ct)
+    {
+        var result = await _pos.GetAsync(poId, ct);
+        if (result is null) return NotFound();
+
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    /// <summary>Create a PO — auto-approved on creation in Phase 1 (FR-PROC-04). Totals computed server-side.</summary>
+    [HttpPost]
+    [ProducesResponseType(typeof(PurchaseOrderDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<PurchaseOrderDto>> Create([FromBody] CreatePurchaseOrderRequest request, CancellationToken ct)
+    {
+        var result = await _pos.CreateAsync(request, ct);
+        SetETag(result.RowVersion);
+        return Created($"/api/v1/purchase-orders/{result.Value.PoId}", result.Value);
+    }
+
+    /// <summary>Edit while open (FR-PROC-05); requires <c>If-Match</c>. 409 PO_NOT_EDITABLE if closed.</summary>
+    [HttpPut("{poId:long}")]
+    [ProducesResponseType(typeof(PurchaseOrderDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status412PreconditionFailed)]
+    public async Task<ActionResult<PurchaseOrderDto>> Update(long poId, [FromBody] UpdatePurchaseOrderRequest request, CancellationToken ct)
+    {
+        var expected = RequireIfMatch();
+        var result = await _pos.UpdateAsync(poId, request, expected, ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    /// <summary>Approve — no-op in Phase 1 (POs auto-approve); transitions PendingApproval→Approved when enabled.</summary>
+    [HttpPost("{poId:long}/approve")]
+    [ProducesResponseType(typeof(PurchaseOrderDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<PurchaseOrderDto>> Approve(long poId, CancellationToken ct)
+        => Ok(await _pos.ApproveAsync(poId, ct));
+
+    /// <summary>Cancel — 409 if any goods have been received against the PO.</summary>
+    [HttpPost("{poId:long}/cancel")]
+    [ProducesResponseType(typeof(PurchaseOrderDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<PurchaseOrderDto>> Cancel(long poId, [FromBody] CancelPurchaseOrderRequest request, CancellationToken ct)
+        => Ok(await _pos.CancelAsync(poId, request.Reason, ct));
+}

Backend/ERPCore/Controllers/PurchaseReturnsController.cs

@@ -0,0 +1,26 @@
+using ERPCore.Dtos.Procurement;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Purchase-return endpoints (docs/11 §3.4).</summary>
+[Route("api/v1/purchase-returns")]
+public sealed class PurchaseReturnsController : ApiControllerBase
+{
+    private readonly IPurchaseReturnService _returns;
+
+    public PurchaseReturnsController(IPurchaseReturnService returns) => _returns = returns;
+
+    /// <summary>Create + auto-post a return (outbound movement). 409 if return exceeds available stock.</summary>
+    [HttpPost]
+    [ProducesResponseType(typeof(PurchaseReturnDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<PurchaseReturnDto>> Create([FromBody] CreatePurchaseReturnRequest request, CancellationToken ct)
+    {
+        var dto = await _returns.CreateAsync(request, ct);
+        return Created($"/api/v1/purchase-returns/{dto.ReturnId}", dto);
+    }
+}

Backend/ERPCore/Controllers/ReasonCodesController.cs

@@ -0,0 +1,31 @@
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Reference;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Reason-code reference endpoints (docs/11 §6).</summary>
+[Route("api/v1/reason-codes")]
+public sealed class ReasonCodesController : ApiControllerBase
+{
+    private readonly IReasonCodeService _codes;
+
+    public ReasonCodesController(IReasonCodeService codes) => _codes = codes;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<ReasonCodeDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<ReasonCodeDto>>> List(
+        [FromQuery] ReasonContext? context, [FromQuery] PageQuery query, CancellationToken ct)
+        => Ok(await _codes.ListAsync(context, query, ct));
+
+    [HttpPost]
+    [ProducesResponseType(typeof(ReasonCodeDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<ReasonCodeDto>> Create([FromBody] CreateReasonCodeRequest request, CancellationToken ct)
+    {
+        var dto = await _codes.CreateAsync(request, ct);
+        return Created($"/api/v1/reason-codes/{dto.ReasonCodeId}", dto);
+    }
+}

Backend/ERPCore/Controllers/RequisitionsController.cs

@@ -0,0 +1,44 @@
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Procurement;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Purchase-requisition endpoints (docs/11 §3.1).</summary>
+[Route("api/v1/requisitions")]
+public sealed class RequisitionsController : ApiControllerBase
+{
+    private readonly IRequisitionService _requisitions;
+
+    public RequisitionsController(IRequisitionService requisitions) => _requisitions = requisitions;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<RequisitionSummaryDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<RequisitionSummaryDto>>> List([FromQuery] PageQuery query, CancellationToken ct)
+        => Ok(await _requisitions.ListAsync(query, ct));
+
+    [HttpGet("{requisitionId:long}")]
+    [ProducesResponseType(typeof(RequisitionDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<RequisitionDto>> GetById(long requisitionId, CancellationToken ct)
+    {
+        var dto = await _requisitions.GetAsync(requisitionId, ct);
+        return dto is null ? NotFound() : Ok(dto);
+    }
+
+    [HttpPost]
+    [ProducesResponseType(typeof(RequisitionDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<RequisitionDto>> Create([FromBody] CreateRequisitionRequest request, CancellationToken ct)
+    {
+        var dto = await _requisitions.CreateAsync(request, ct);
+        return Created($"/api/v1/requisitions/{dto.RequisitionId}", dto);
+    }
+
+    [HttpPost("{requisitionId:long}/submit")]
+    [ProducesResponseType(typeof(RequisitionDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<RequisitionDto>> Submit(long requisitionId, CancellationToken ct)
+        => Ok(await _requisitions.SubmitAsync(requisitionId, ct));
+}

Backend/ERPCore/Controllers/RfqsController.cs

@@ -0,0 +1,49 @@
+using ERPCore.Dtos.Procurement;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>RFQ &amp; quotation endpoints (docs/11 §3.2).</summary>
+[Route("api/v1/rfqs")]
+public sealed class RfqsController : ApiControllerBase
+{
+    private readonly IRfqService _rfqs;
+
+    public RfqsController(IRfqService rfqs) => _rfqs = rfqs;
+
+    [HttpGet("{rfqId:long}")]
+    [ProducesResponseType(typeof(RfqDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<RfqDto>> GetById(long rfqId, CancellationToken ct)
+    {
+        var dto = await _rfqs.GetAsync(rfqId, ct);
+        return dto is null ? NotFound() : Ok(dto);
+    }
+
+    [HttpPost]
+    [ProducesResponseType(typeof(RfqDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<RfqDto>> Create([FromBody] CreateRfqRequest request, CancellationToken ct)
+    {
+        var dto = await _rfqs.CreateAsync(request, ct);
+        return Created($"/api/v1/rfqs/{dto.RfqId}", dto);
+    }
+
+    [HttpPost("{rfqId:long}/quotations")]
+    [ProducesResponseType(typeof(VendorQuotationDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<VendorQuotationDto>> AddQuotation(long rfqId, [FromBody] CreateQuotationRequest request, CancellationToken ct)
+    {
+        var dto = await _rfqs.AddQuotationAsync(rfqId, request, ct);
+        return Created($"/api/v1/rfqs/{rfqId}/quotations/{dto.QuotationId}", dto);
+    }
+
+    [HttpGet("{rfqId:long}/comparison")]
+    [ProducesResponseType(typeof(RfqComparisonDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<RfqComparisonDto>> Comparison(long rfqId, CancellationToken ct)
+        => Ok(await _rfqs.GetComparisonAsync(rfqId, ct));
+}

Backend/ERPCore/Controllers/StockAdjustmentsController.cs

@@ -0,0 +1,26 @@
+using ERPCore.Dtos.Stock;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Stock-adjustment endpoints (docs/11 §5.5).</summary>
+[Route("api/v1/stock-adjustments")]
+public sealed class StockAdjustmentsController : ApiControllerBase
+{
+    private readonly IAdjustmentService _adjustments;
+
+    public StockAdjustmentsController(IAdjustmentService adjustments) => _adjustments = adjustments;
+
+    /// <summary>Create + auto-post an adjustment (mandatory reason code; decrease FIFO-consumes).</summary>
+    [HttpPost]
+    [ProducesResponseType(typeof(AdjustmentDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<AdjustmentDto>> Create([FromBody] CreateAdjustmentRequest request, CancellationToken ct)
+    {
+        var dto = await _adjustments.CreateAsync(request, ct);
+        return Created($"/api/v1/stock-adjustments/{dto.AdjustmentId}", dto);
+    }
+}

Backend/ERPCore/Controllers/StockController.cs

@@ -0,0 +1,56 @@
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Procurement;
+using ERPCore.Dtos.Stock;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Stock enquiry, ledger, valuation and reorder-alert endpoints (docs/11 §5.1–5.3, §5.7).</summary>
+[Route("api/v1/stock")]
+public sealed class StockController : ApiControllerBase
+{
+    private readonly IStockService _stock;
+    private readonly IReorderService _reorder;
+
+    public StockController(IStockService stock, IReorderService reorder)
+    {
+        _stock = stock;
+        _reorder = reorder;
+    }
+
+    [HttpGet("on-hand")]
+    [ProducesResponseType(typeof(StockOnHandDto), StatusCodes.Status200OK)]
+    public async Task<ActionResult<StockOnHandDto>> OnHand([FromQuery] long itemId, [FromQuery] long warehouseId, CancellationToken ct)
+        => Ok(await _stock.GetOnHandAsync(itemId, warehouseId, ct));
+
+    [HttpGet("ledger")]
+    [ProducesResponseType(typeof(PagedResponse<StockLedgerRowDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<StockLedgerRowDto>>> Ledger(
+        [FromQuery] long? itemId, [FromQuery] long? warehouseId,
+        [FromQuery] DateOnly? from, [FromQuery] DateOnly? to, [FromQuery] PageQuery query, CancellationToken ct)
+        => Ok(await _stock.GetLedgerAsync(itemId, warehouseId, from, to, query, ct));
+
+    [HttpGet("valuation")]
+    [ProducesResponseType(typeof(StockValuationDto), StatusCodes.Status200OK)]
+    public async Task<ActionResult<StockValuationDto>> Valuation([FromQuery] long itemId, [FromQuery] long warehouseId, CancellationToken ct)
+        => Ok(await _stock.GetValuationAsync(itemId, warehouseId, ct));
+
+    /// <summary>Items at/below their reorder point (FR-STK-10), computed on read.</summary>
+    [HttpGet("reorder-alerts")]
+    [ProducesResponseType(typeof(PagedResponse<ReorderAlertDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<ReorderAlertDto>>> ReorderAlerts(
+        [FromQuery] long? warehouseId, [FromQuery] PageQuery query, CancellationToken ct)
+        => Ok(await _reorder.GetAlertsAsync(warehouseId, query, ct));
+
+    /// <summary>Create a draft requisition for an item's suggested reorder quantity.</summary>
+    [HttpPost("reorder-alerts/{itemId:long}/requisition")]
+    [ProducesResponseType(typeof(RequisitionDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<RequisitionDto>> SuggestRequisition(
+        long itemId, [FromQuery] long warehouseId, CancellationToken ct)
+    {
+        var dto = await _reorder.CreateSuggestedRequisitionAsync(itemId, warehouseId, ct);
+        return Created($"/api/v1/requisitions/{dto.RequisitionId}", dto);
+    }
+}

Backend/ERPCore/Controllers/StockCountsController.cs

@@ -0,0 +1,49 @@
+using ERPCore.Dtos.Stock;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Stock-count endpoints (docs/11 §5.6).</summary>
+[Route("api/v1/stock-counts")]
+public sealed class StockCountsController : ApiControllerBase
+{
+    private readonly ICountService _counts;
+
+    public StockCountsController(ICountService counts) => _counts = counts;
+
+    [HttpGet("{countId:long}")]
+    [ProducesResponseType(typeof(CountDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<CountDto>> GetById(long countId, CancellationToken ct)
+    {
+        var dto = await _counts.GetAsync(countId, ct);
+        return dto is null ? NotFound() : Ok(dto);
+    }
+
+    /// <summary>Create a count with system quantities snapshotted (immutable).</summary>
+    [HttpPost]
+    [ProducesResponseType(typeof(CountDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<CountDto>> Create([FromBody] CreateCountRequest request, CancellationToken ct)
+    {
+        var dto = await _counts.CreateAsync(request, ct);
+        return Created($"/api/v1/stock-counts/{dto.CountId}", dto);
+    }
+
+    /// <summary>Enter counted quantities; variance = counted − system.</summary>
+    [HttpPut("{countId:long}/counts")]
+    [ProducesResponseType(typeof(CountDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<CountDto>> EnterCounts(long countId, [FromBody] EnterCountsRequest request, CancellationToken ct)
+        => Ok(await _counts.EnterCountsAsync(countId, request, ct));
+
+    /// <summary>Post: emit a variance adjustment and close the count.</summary>
+    [HttpPost("{countId:long}/post")]
+    [ProducesResponseType(typeof(CountPostResultDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<CountPostResultDto>> Post(long countId, CancellationToken ct)
+        => Ok(await _counts.PostAsync(countId, ct));
+}

Backend/ERPCore/Controllers/StockTransfersController.cs

@@ -0,0 +1,49 @@
+using ERPCore.Dtos.Stock;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Stock-transfer endpoints (docs/11 §5.4).</summary>
+[Route("api/v1/stock-transfers")]
+public sealed class StockTransfersController : ApiControllerBase
+{
+    private readonly ITransferService _transfers;
+
+    public StockTransfersController(ITransferService transfers) => _transfers = transfers;
+
+    [HttpGet("{transferId:long}")]
+    [ProducesResponseType(typeof(TransferDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<TransferDto>> GetById(long transferId, CancellationToken ct)
+    {
+        var dto = await _transfers.GetAsync(transferId, ct);
+        return dto is null ? NotFound() : Ok(dto);
+    }
+
+    [HttpPost]
+    [ProducesResponseType(typeof(TransferDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<TransferDto>> Create([FromBody] CreateTransferRequest request, CancellationToken ct)
+    {
+        var dto = await _transfers.CreateAsync(request, ct);
+        return Created($"/api/v1/stock-transfers/{dto.TransferId}", dto);
+    }
+
+    /// <summary>Dispatch: consume source FIFO layers into in-transit. 409 STOCK_NEGATIVE_BLOCKED if short.</summary>
+    [HttpPost("{transferId:long}/dispatch")]
+    [ProducesResponseType(typeof(DispatchResultDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<DispatchResultDto>> Dispatch(long transferId, CancellationToken ct)
+        => Ok(await _transfers.DispatchAsync(transferId, ct));
+
+    /// <summary>Receive: create the destination layer at the inherited cost (cost-preserving).</summary>
+    [HttpPost("{transferId:long}/receive")]
+    [ProducesResponseType(typeof(ReceiveResultDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<ReceiveResultDto>> Receive(long transferId, [FromBody] ReceiveTransferRequest request, CancellationToken ct)
+        => Ok(await _transfers.ReceiveAsync(transferId, request, ct));
+}

Backend/ERPCore/Controllers/UomsController.cs

@@ -0,0 +1,29 @@
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Uoms;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Unit-of-measure endpoints (docs/11-BACKEND-PHASE1.md §2.2).</summary>
+[Route("api/v1/uoms")]
+public sealed class UomsController : ApiControllerBase
+{
+    private readonly IUomService _uoms;
+
+    public UomsController(IUomService uoms) => _uoms = uoms;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<UomDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<UomDto>>> List([FromQuery] PageQuery query, CancellationToken ct)
+        => Ok(await _uoms.ListAsync(query, ct));
+
+    [HttpPost]
+    [ProducesResponseType(typeof(UomDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<UomDto>> Create([FromBody] CreateUomRequest request, CancellationToken ct)
+    {
+        var dto = await _uoms.CreateAsync(request, ct);
+        return Created($"/api/v1/uoms/{dto.UomId}", dto);
+    }
+}

Backend/ERPCore/Controllers/VendorsController.cs

@@ -0,0 +1,65 @@
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Vendors;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Vendor master endpoints (docs/11-BACKEND-PHASE1.md §2.4).</summary>
+[Route("api/v1/vendors")]
+public sealed class VendorsController : ApiControllerBase
+{
+    private readonly IVendorService _vendors;
+
+    public VendorsController(IVendorService vendors) => _vendors = vendors;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<VendorDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<VendorDto>>> List(
+        [FromQuery] PageQuery query, [FromQuery] EntityStatus? status, CancellationToken ct)
+        => Ok(await _vendors.ListAsync(query, status, ct));
+
+    [HttpGet("{vendorId:long}")]
+    [ProducesResponseType(typeof(VendorDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<VendorDto>> GetById(long vendorId, CancellationToken ct)
+    {
+        var result = await _vendors.GetAsync(vendorId, ct);
+        if (result is null) return NotFound();
+
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    [HttpPost]
+    [ProducesResponseType(typeof(VendorDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<VendorDto>> Create([FromBody] CreateVendorRequest request, CancellationToken ct)
+    {
+        var result = await _vendors.CreateAsync(request, ct);
+        SetETag(result.RowVersion);
+        return Created($"/api/v1/vendors/{result.Value.VendorId}", result.Value);
+    }
+
+    [HttpPut("{vendorId:long}")]
+    [ProducesResponseType(typeof(VendorDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status412PreconditionFailed)]
+    public async Task<ActionResult<VendorDto>> Update(long vendorId, [FromBody] UpdateVendorRequest request, CancellationToken ct)
+    {
+        var expected = RequireIfMatch();
+        var result = await _vendors.UpdateAsync(vendorId, request, expected, ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    [HttpPatch("{vendorId:long}/status")]
+    [ProducesResponseType(StatusCodes.Status204NoContent)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> SetStatus(long vendorId, [FromBody] UpdateVendorStatusRequest request, CancellationToken ct)
+    {
+        await _vendors.SetStatusAsync(vendorId, request.Status, ct);
+        return NoContent();
+    }
+}

Backend/ERPCore/Controllers/WarehousesController.cs

@@ -0,0 +1,54 @@
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Warehouses;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Warehouse &amp; bin endpoints (docs/11-BACKEND-PHASE1.md §2.5).</summary>
+[Route("api/v1/warehouses")]
+public sealed class WarehousesController : ApiControllerBase
+{
+    private readonly IWarehouseService _warehouses;
+
+    public WarehousesController(IWarehouseService warehouses) => _warehouses = warehouses;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<WarehouseDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<WarehouseDto>>> List([FromQuery] PageQuery query, CancellationToken ct)
+        => Ok(await _warehouses.ListAsync(query, ct));
+
+    [HttpGet("{warehouseId:long}")]
+    [ProducesResponseType(typeof(WarehouseDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<WarehouseDto>> GetById(long warehouseId, CancellationToken ct)
+    {
+        var dto = await _warehouses.GetAsync(warehouseId, ct);
+        return dto is null ? NotFound() : Ok(dto);
+    }
+
+    [HttpPost]
+    [ProducesResponseType(typeof(WarehouseDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<WarehouseDto>> Create([FromBody] CreateWarehouseRequest request, CancellationToken ct)
+    {
+        var dto = await _warehouses.CreateAsync(request, ct);
+        return Created($"/api/v1/warehouses/{dto.WarehouseId}", dto);
+    }
+
+    [HttpGet("{warehouseId:long}/bins")]
+    [ProducesResponseType(typeof(IReadOnlyList<BinDto>), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<IReadOnlyList<BinDto>>> ListBins(long warehouseId, CancellationToken ct)
+        => Ok(await _warehouses.ListBinsAsync(warehouseId, ct));
+
+    [HttpPost("{warehouseId:long}/bins")]
+    [ProducesResponseType(typeof(BinDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<BinDto>> CreateBin(long warehouseId, [FromBody] CreateBinRequest request, CancellationToken ct)
+    {
+        var dto = await _warehouses.CreateBinAsync(warehouseId, request, ct);
+        return Created($"/api/v1/warehouses/{warehouseId}/bins/{dto.BinId}", dto);
+    }
+}

Backend/ERPCore/Domain/DocumentTypes.cs

@@ -0,0 +1,17 @@
+namespace ERPCore.Domain;
+
+/// <summary>
+/// Document-type prefixes for <see cref="Entities.NumberSequence"/> and the
+/// generated document numbers (docs/10 §B.8.2). One prefix per numbered document.
+/// </summary>
+public static class DocumentTypes
+{
+    public const string Requisition = "PR";
+    public const string Rfq = "RFQ";
+    public const string PurchaseOrder = "PO";
+    public const string Grn = "GRN";
+    public const string Transfer = "TRF";
+    public const string Adjustment = "ADJ";
+    public const string Count = "CNT";
+    public const string PurchaseReturn = "PRET";
+}

Backend/ERPCore/Domain/Entities/AuditLog.cs

@@ -0,0 +1,23 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Immutable audit trail entry (FR-X-02) — the compensating control for the deferred
+/// RBAC (02-SECURITY AR-01/B.3). One row per create/update/delete of an audited
+/// entity, capturing who / when / what changed (old→new in <see cref="ChangeSet"/>).
+/// Written automatically by <c>ErpDbContext.SaveChangesAsync</c>. Append-only at the
+/// app level; DB-role revocation of UPDATE/DELETE is deferred hardening (B.3).
+/// Model: docs/10 Part C.7.
+/// </summary>
+public class AuditLog
+{
+    public long AuditId { get; set; }
+    public long UserId { get; set; }
+    public string EntityType { get; set; } = string.Empty;
+    public long EntityId { get; set; }
+    public AuditAction Action { get; set; }
+    /// <summary>JSON change set: field→value (create/delete) or field→{old,new} (update).</summary>
+    public string ChangeSet { get; set; } = "{}";
+    public DateTime CreatedAt { get; set; }
+}

Backend/ERPCore/Domain/Entities/Batch.cs

@@ -0,0 +1,16 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Batch/lot for a batch-tracked item (FR-GRN-04, FR-WH-03). Expiry drives FEFO
+/// picking of perishables. Model: docs/10 Part C.4.
+/// </summary>
+public class Batch
+{
+    public long BatchId { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public string BatchNo { get; set; } = string.Empty;
+    public DateOnly? ExpiryDate { get; set; }
+}

Backend/ERPCore/Domain/Entities/Bin.cs

@@ -0,0 +1,16 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Bin / storage location within a warehouse (FR-MD-07, FR-WH-02). Stock is
+/// tracked to bin level. Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// </summary>
+public class Bin
+{
+    public long BinId { get; set; }
+
+    public long WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public string Code { get; set; } = string.Empty;
+    public string? BinType { get; set; }
+}

Backend/ERPCore/Domain/Entities/Category.cs

@@ -0,0 +1,15 @@
+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.
+/// </summary>
+public class Category
+{
+    public long CategoryId { get; set; }
+    public string Name { get; set; } = string.Empty;
+
+    public long? ParentId { get; set; }
+    public Category? Parent { get; set; }
+    public ICollection<Category> Children { get; set; } = new List<Category>();
+}

Backend/ERPCore/Domain/Entities/Grn.cs

@@ -0,0 +1,37 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Goods Receipt Note header (FR-GRN-01/02). Raised against a PO or direct
+/// (<see cref="PoId"/> null). On confirm each line creates a FIFO layer and posts
+/// an inbound ledger entry. Mutable aggregate with an <see cref="RowVersion"/>
+/// concurrency token (docs/10 C.10). Model: docs/10 Part C.3.
+/// </summary>
+public class Grn
+{
+    public long GrnId { get; set; }
+    public string DocNo { get; set; } = string.Empty;
+
+    public long? PoId { get; set; }
+    public PurchaseOrder? PurchaseOrder { get; set; }
+
+    public long VendorId { get; set; }
+    public Vendor? Vendor { get; set; }
+
+    public long WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public GrnStatus Status { get; set; } = GrnStatus.Draft;
+
+    public long CreatedBy { get; set; }
+    public User? Creator { get; set; }
+
+    public DateTime CreatedAt { get; set; }
+    public DateTime? PostedAt { get; set; }
+
+    /// <summary>PostgreSQL xmin-backed optimistic concurrency token.</summary>
+    public uint RowVersion { get; set; }
+
+    public ICollection<GrnLine> Lines { get; set; } = new List<GrnLine>();
+}

Backend/ERPCore/Domain/Entities/GrnLine.cs

@@ -0,0 +1,37 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// GRN line (FR-GRN-04..08). <see cref="UnitCost"/> is the PO-derived cost for
+/// PO-based receipts (client cost ignored — 02-SECURITY C.3) or the entered cost
+/// for direct receipts. <see cref="ReceivedValue"/> = qty × unitCost.
+/// <see cref="HoldStatus"/> gates issuability. Model: docs/10 Part C.3.
+/// </summary>
+public class GrnLine
+{
+    public long GrnLineId { get; set; }
+
+    public long GrnId { get; set; }
+    public Grn? Grn { get; set; }
+
+    public long? PoLineId { get; set; }
+    public PoLine? PoLine { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public long UomId { get; set; }
+    public Uom? Uom { get; set; }
+
+    public long? BinId { get; set; }
+    public Bin? Bin { get; set; }
+
+    public long? BatchId { get; set; }
+    public Batch? Batch { get; set; }
+
+    public decimal Qty { get; set; }
+    public decimal UnitCost { get; set; }
+    public decimal ReceivedValue { get; set; }
+    public HoldStatus HoldStatus { get; set; } = HoldStatus.Available;
+}

Backend/ERPCore/Domain/Entities/Item.cs

@@ -0,0 +1,39 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Item master (FR-MD-01). Mutable aggregate: carries a <see cref="RowVersion"/>
+/// concurrency token surfaced as an ETag (docs/10 Part C.10). SKU is unique.
+/// Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// </summary>
+public class Item
+{
+    public long ItemId { get; set; }
+    public string Sku { get; set; } = string.Empty;
+    public string Name { get; set; } = string.Empty;
+    public string? Description { get; set; }
+
+    public long CategoryId { get; set; }
+    public Category? Category { get; set; }
+
+    public long BaseUomId { get; set; }
+    public Uom? BaseUom { get; set; }
+
+    public long? DefaultVendorId { get; set; }
+    public Vendor? DefaultVendor { get; set; }
+
+    public ItemType ItemType { get; set; }
+    public TrackingMode TrackingMode { get; set; }
+    public string? TaxClass { 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; }
+
+    public ICollection<ItemReorder> ReorderSettings { get; set; } = new List<ItemReorder>();
+    public ICollection<UomConversion> UomConversions { get; set; } = new List<UomConversion>();
+}

Backend/ERPCore/Domain/Entities/ItemReorder.cs

@@ -0,0 +1,20 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Reorder policy for an item, optionally per warehouse (FR-MD-05). Reorder alerts
+/// are computed from these versus available stock (FR-STK-10) — not stored.
+/// Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// </summary>
+public class ItemReorder
+{
+    public long ReorderId { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public long WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public decimal ReorderPoint { get; set; }
+    public decimal ReorderQty { get; set; }
+}

Backend/ERPCore/Domain/Entities/JournalEntryStub.cs

@@ -0,0 +1,18 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// GL-ready journal entry emitted per stock movement (FR-STK-13) — data only, no
+/// posting in Phase 1 (the Accounting module consumes these later). One row per
+/// ledger entry, referencing the same source document polymorphically. Account
+/// codes are Phase-1 placeholders until a chart of accounts exists.
+/// Model: docs/10 Part C.7.
+/// </summary>
+public class JournalEntryStub
+{
+    public long JournalId { get; set; }
+    public string SourceDocType { get; set; } = string.Empty;
+    public long SourceDocId { get; set; }
+    public string DebitAccount { get; set; } = string.Empty;
+    public string CreditAccount { get; set; } = string.Empty;
+    public decimal Amount { get; set; }
+}

Backend/ERPCore/Domain/Entities/NumberSequence.cs

@@ -0,0 +1,15 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Per-document-type, per-year running counter behind human document numbers
+/// (FR-X-03): <c>PR-2026-00001</c>, <c>PO-2026-00042</c>, … Numbers are issued
+/// inside the document's transaction so they are unique and gap-controlled.
+/// Model: docs/10 Part C.7.
+/// </summary>
+public class NumberSequence
+{
+    public long SequenceId { get; set; }
+    public string DocType { get; set; } = string.Empty;
+    public int Year { get; set; }
+    public long LastNumber { get; set; }
+}

Backend/ERPCore/Domain/Entities/PoLine.cs

@@ -0,0 +1,28 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Purchase-order line (FR-PROC-03). <see cref="Tax"/> is the line tax rate
+/// (e.g. 0.18); <see cref="QtyReceived"/> accrues as GRNs confirm (FR-PROC-07).
+/// Model: docs/10 Part C.2.
+/// </summary>
+public class PoLine
+{
+    public long PoLineId { get; set; }
+
+    public long PoId { get; set; }
+    public PurchaseOrder? PurchaseOrder { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public long UomId { get; set; }
+    public Uom? Uom { get; set; }
+
+    public long WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public decimal Qty { get; set; }
+    public decimal UnitPrice { get; set; }
+    public decimal Tax { get; set; }
+    public decimal QtyReceived { get; set; }
+}

Backend/ERPCore/Domain/Entities/PurchaseOrder.cs

@@ -0,0 +1,36 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Purchase order header (FR-PROC-03..06). Mutable aggregate with a
+/// <see cref="RowVersion"/> ETag token; editable while open (FR-PROC-05).
+/// Phase 1 auto-approves on creation; <see cref="ApprovalRequired"/> is retained
+/// for the future approval workflow. Totals are computed server-side from lines
+/// (not stored). Model: docs/10 Part C.2.
+/// </summary>
+public class PurchaseOrder
+{
+    public long PoId { get; set; }
+    public string DocNo { get; set; } = string.Empty;
+
+    public long VendorId { get; set; }
+    public Vendor? Vendor { get; set; }
+
+    public long? RequisitionId { get; set; }
+    public Requisition? Requisition { get; set; }
+
+    public PurchaseOrderStatus Status { get; set; } = PurchaseOrderStatus.Draft;
+    public bool ApprovalRequired { get; set; }
+
+    public long CreatedBy { get; set; }
+    public User? Creator { get; set; }
+
+    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<PoLine> Lines { get; set; } = new List<PoLine>();
+}

Backend/ERPCore/Domain/Entities/PurchaseReturn.cs

@@ -0,0 +1,32 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Purchase return header (FR-PROC-08) — returns received goods to a vendor,
+/// generating an outbound stock movement. Auto-posts with a mandatory reason code.
+/// Model: docs/10 Part C.2.
+/// </summary>
+public class PurchaseReturn
+{
+    public long ReturnId { get; set; }
+    public string DocNo { get; set; } = string.Empty;
+
+    public long VendorId { get; set; }
+    public Vendor? Vendor { get; set; }
+
+    public long WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public long ReasonCodeId { get; set; }
+    public ReasonCode? ReasonCode { get; set; }
+
+    public ReturnStatus Status { get; set; } = ReturnStatus.Posted;
+
+    public long CreatedBy { get; set; }
+    public User? Creator { get; set; }
+
+    public DateTime CreatedAt { get; set; }
+
+    public ICollection<PurchaseReturnLine> Lines { get; set; } = new List<PurchaseReturnLine>();
+}

Backend/ERPCore/Domain/Entities/PurchaseReturnLine.cs

@@ -0,0 +1,21 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Purchase-return line (FR-PROC-08) referencing the original GRN line for
+/// traceability. <see cref="Qty"/> is in base UOM. Model: docs/10 Part C.2.
+/// </summary>
+public class PurchaseReturnLine
+{
+    public long ReturnLineId { get; set; }
+
+    public long ReturnId { get; set; }
+    public PurchaseReturn? Return { get; set; }
+
+    public long? GrnLineId { get; set; }
+    public GrnLine? GrnLine { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public decimal Qty { get; set; }
+}

Backend/ERPCore/Domain/Entities/ReasonCode.cs

@@ -0,0 +1,15 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Configurable reason code for adjustments, returns and count variances
+/// (FR-X-04). Model: docs/10 Part C.7.
+/// </summary>
+public class ReasonCode
+{
+    public long ReasonCodeId { get; set; }
+    public string Code { get; set; } = string.Empty;
+    public string Description { get; set; } = string.Empty;
+    public ReasonContext Context { get; set; }
+}

Backend/ERPCore/Domain/Entities/Requisition.cs

@@ -0,0 +1,21 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Purchase requisition header (FR-PROC-01). <see cref="RequestedBy"/> is the audit
+/// actor from the token (never the body). Model: docs/10 Part C.2.
+/// </summary>
+public class Requisition
+{
+    public long RequisitionId { get; set; }
+    public string DocNo { get; set; } = string.Empty;
+
+    public long RequestedBy { get; set; }
+    public User? Requester { get; set; }
+
+    public RequisitionStatus Status { get; set; } = RequisitionStatus.Draft;
+    public DateTime CreatedAt { get; set; }
+
+    public ICollection<RequisitionLine> Lines { get; set; } = new List<RequisitionLine>();
+}

Backend/ERPCore/Domain/Entities/RequisitionLine.cs

@@ -0,0 +1,16 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>Requisition line (FR-PROC-01). Model: docs/10 Part C.2.</summary>
+public class RequisitionLine
+{
+    public long ReqLineId { get; set; }
+
+    public long RequisitionId { get; set; }
+    public Requisition? Requisition { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public decimal Qty { get; set; }
+    public DateOnly? RequiredBy { get; set; }
+}

Backend/ERPCore/Domain/Entities/Rfq.cs

@@ -0,0 +1,22 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Request for Quotation header (FR-PROC-02) raised from a requisition. Vendor
+/// quotations attach for comparison. Model: docs/10 Part C.2.
+/// </summary>
+public class Rfq
+{
+    public long RfqId { get; set; }
+    public string DocNo { get; set; } = string.Empty;
+
+    public long RequisitionId { get; set; }
+    public Requisition? Requisition { get; set; }
+
+    public RfqStatus Status { get; set; } = RfqStatus.Open;
+    public DateTime CreatedAt { get; set; }
+
+    public ICollection<RfqLine> Lines { get; set; } = new List<RfqLine>();
+    public ICollection<VendorQuotation> Quotations { get; set; } = new List<VendorQuotation>();
+}

Backend/ERPCore/Domain/Entities/RfqLine.cs

@@ -0,0 +1,15 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>RFQ line — an item + quantity being quoted (FR-PROC-02). Model: docs/10 Part C.2.</summary>
+public class RfqLine
+{
+    public long RfqLineId { get; set; }
+
+    public long RfqId { get; set; }
+    public Rfq? Rfq { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public decimal Qty { get; set; }
+}

Backend/ERPCore/Domain/Entities/Serial.cs

@@ -0,0 +1,16 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Serial number for a serial-tracked item across its lifecycle (FR-WH-04).
+/// Model: docs/10 Part C.4.
+/// </summary>
+public class Serial
+{
+    public long SerialId { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public string SerialNo { get; set; } = string.Empty;
+    public string Status { get; set; } = "InStock";
+}

Backend/ERPCore/Domain/Entities/StockAdjustment.cs

@@ -0,0 +1,31 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Stock adjustment header (FR-STK-07) — the highest-risk feature in the phase
+/// (02-SECURITY C.5). Auto-posts in Phase 1 with a mandatory reason code and user
+/// stamp. Mutable aggregate with an <see cref="RowVersion"/> token (docs/10 C.10).
+/// Model: docs/10 Part C.6.
+/// </summary>
+public class StockAdjustment
+{
+    public long AdjustmentId { get; set; }
+    public string DocNo { get; set; } = string.Empty;
+
+    public long WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public long ReasonCodeId { get; set; }
+    public ReasonCode? ReasonCode { get; set; }
+
+    public AdjustmentStatus Status { get; set; } = AdjustmentStatus.Posted;
+
+    public long CreatedBy { get; set; }
+    public User? Creator { get; set; }
+
+    public DateTime CreatedAt { get; set; }
+    public uint RowVersion { get; set; }
+
+    public ICollection<StockAdjustmentLine> Lines { get; set; } = new List<StockAdjustmentLine>();
+}

Backend/ERPCore/Domain/Entities/StockAdjustmentLine.cs

@@ -0,0 +1,23 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Adjustment line (FR-STK-07). <see cref="QtyDelta"/> is a signed base-UOM
+/// quantity: negative consumes FIFO layers, positive creates a layer at last cost.
+/// Model: docs/10 Part C.6.
+/// </summary>
+public class StockAdjustmentLine
+{
+    public long AdjLineId { get; set; }
+
+    public long AdjustmentId { get; set; }
+    public StockAdjustment? Adjustment { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public long? BinId { get; set; }
+    public long? BatchId { get; set; }
+    public long? SerialId { get; set; }
+
+    public decimal QtyDelta { get; set; }
+}

Backend/ERPCore/Domain/Entities/StockCount.cs

@@ -0,0 +1,29 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Cycle/full physical count header (FR-STK-08). System quantities are snapshotted
+/// at creation and are immutable once opened (02-SECURITY C.7); posting emits a
+/// variance adjustment. Mutable aggregate with an <see cref="RowVersion"/> token.
+/// Model: docs/10 Part C.6.
+/// </summary>
+public class StockCount
+{
+    public long CountId { get; set; }
+    public string DocNo { get; set; } = string.Empty;
+
+    public long WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public CountType CountType { get; set; }
+    public CountStatus Status { get; set; } = CountStatus.Draft;
+
+    public long CreatedBy { get; set; }
+    public User? Creator { get; set; }
+
+    public DateTime CreatedAt { get; set; }
+    public uint RowVersion { get; set; }
+
+    public ICollection<StockCountLine> Lines { get; set; } = new List<StockCountLine>();
+}

Backend/ERPCore/Domain/Entities/StockCountLine.cs

@@ -0,0 +1,22 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Count line (FR-STK-08). <see cref="SystemQty"/> is the immutable snapshot;
+/// <see cref="Variance"/> = counted − system (in base UOM). Model: docs/10 Part C.6.
+/// </summary>
+public class StockCountLine
+{
+    public long CountLineId { get; set; }
+
+    public long CountId { get; set; }
+    public StockCount? Count { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public long? BinId { get; set; }
+
+    public decimal SystemQty { get; set; }
+    public decimal? CountedQty { get; set; }
+    public decimal? Variance { get; set; }
+}

Backend/ERPCore/Domain/Entities/StockLayer.cs

@@ -0,0 +1,33 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// FIFO cost layer — a quantity received at a specific unit cost, consumed
+/// oldest-first (FR-STK-02). Keyed per item **per warehouse**; quantities and
+/// <see cref="UnitCost"/> are in the item's base UOM. Answers valuation
+/// ("what's on hand and at what cost"). Model: docs/10 Part C.5.
+/// </summary>
+public class StockLayer
+{
+    public long LayerId { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public long WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public long? BatchId { get; set; }
+    public Batch? Batch { get; set; }
+
+    public long? SerialId { get; set; }
+    public Serial? Serial { get; set; }
+
+    /// <summary>Originating GRN line — carries the inspection hold status for this stock.</summary>
+    public long? GrnLineId { get; set; }
+    public GrnLine? GrnLine { get; set; }
+
+    public decimal QtyReceived { get; set; }
+    public decimal QtyRemaining { get; set; }
+    public decimal UnitCost { get; set; }
+    public DateTime ReceiptDate { get; set; }
+}

Backend/ERPCore/Domain/Entities/StockLedger.cs

@@ -0,0 +1,32 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Immutable, append-only stock ledger (FR-STK-01, FR-X-05). One row per costed
+/// movement; answers history ("what moved, when, by whom"). The originating
+/// document is referenced polymorphically via
+/// <see cref="SourceDocType"/>/<see cref="SourceDocId"/> (no hard FK per type) so
+/// new transaction types write here without a schema change. Model: docs/10 Part C.5.
+/// </summary>
+public class StockLedger
+{
+    public long LedgerId { get; set; }
+
+    public long ItemId { get; set; }
+    public long WarehouseId { get; set; }
+    public long? BinId { get; set; }
+    public long? BatchId { get; set; }
+    public long? SerialId { get; set; }
+    public long UserId { get; set; }
+
+    public Direction Direction { get; set; }
+    public decimal QtyBase { get; set; }
+    public decimal UnitCost { get; set; }
+    public decimal Value { get; set; }
+    public decimal RunningBalance { get; set; }
+
+    public string SourceDocType { get; set; } = string.Empty;
+    public long SourceDocId { get; set; }
+    public DateTime CreatedAt { get; set; }
+}

Backend/ERPCore/Domain/Entities/StockTransfer.cs

@@ -0,0 +1,31 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Inter-warehouse stock transfer header (FR-STK-05/06). Dispatch consumes source
+/// FIFO layers into in-transit; receive creates the destination layer at the
+/// inherited cost (cost-preserving). Mutable aggregate with an
+/// <see cref="RowVersion"/> token (docs/10 C.10). Model: docs/10 Part C.6.
+/// </summary>
+public class StockTransfer
+{
+    public long TransferId { get; set; }
+    public string DocNo { get; set; } = string.Empty;
+
+    public long SrcWarehouseId { get; set; }
+    public Warehouse? SrcWarehouse { get; set; }
+
+    public long DestWarehouseId { get; set; }
+    public Warehouse? DestWarehouse { get; set; }
+
+    public TransferStatus Status { get; set; } = TransferStatus.Draft;
+
+    public long CreatedBy { get; set; }
+    public User? Creator { get; set; }
+
+    public DateTime CreatedAt { get; set; }
+    public uint RowVersion { get; set; }
+
+    public ICollection<StockTransferLine> Lines { get; set; } = new List<StockTransferLine>();
+}

Backend/ERPCore/Domain/Entities/StockTransferLine.cs

@@ -0,0 +1,35 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Transfer line (FR-STK-05/06). <see cref="Qty"/> is in base UOM.
+/// <para>
+/// Deviation note: <see cref="UnitCost"/> and <see cref="QtyReceived"/> extend
+/// docs/10 Part C.6's <c>STOCK_TRANSFER_LINE</c> to make the transfer
+/// cost-preserving: at dispatch the value-weighted cost of the consumed source
+/// layers is stored here, and receive recreates the destination layer at that cost
+/// (supports partial receive via <see cref="QtyReceived"/>).
+/// </para>
+/// </summary>
+public class StockTransferLine
+{
+    public long TransferLineId { get; set; }
+
+    public long TransferId { get; set; }
+    public StockTransfer? Transfer { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public long? SrcBinId { get; set; }
+    public long? DestBinId { get; set; }
+    public long? BatchId { get; set; }
+    public long? SerialId { get; set; }
+
+    public decimal Qty { get; set; }
+
+    /// <summary>Value-weighted unit cost of the consumed source layers (set at dispatch).</summary>
+    public decimal? UnitCost { get; set; }
+
+    /// <summary>Quantity already received at the destination (partial-receive support).</summary>
+    public decimal QtyReceived { get; set; }
+}

Backend/ERPCore/Domain/Entities/Uom.cs

@@ -0,0 +1,11 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Unit of Measure (FR-MD-02). Referenced as an item's base UOM and as the
+/// endpoints of a <see cref="UomConversion"/>. Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// </summary>
+public class Uom
+{
+    public long UomId { get; set; }
+    public string Name { get; set; } = string.Empty;
+}

Backend/ERPCore/Domain/Entities/UomConversion.cs

@@ -0,0 +1,22 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Per-item conversion factor between two UOMs (FR-MD-02/03): quantity in
+/// <see cref="FromUomId"/> × <see cref="Factor"/> = quantity in <see cref="ToUomId"/>.
+/// Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// </summary>
+public class UomConversion
+{
+    public long ConversionId { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public long FromUomId { get; set; }
+    public Uom? FromUom { get; set; }
+
+    public long ToUomId { get; set; }
+    public Uom? ToUom { get; set; }
+
+    public decimal Factor { get; set; }
+}

Backend/ERPCore/Domain/Entities/User.cs

@@ -0,0 +1,25 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Application user (FR-X-01) — a **local shadow/projection** of an AuthHex identity.
+/// The local <see cref="UserId"/> (long) is what every `createdBy`/`requestedBy`/
+/// audit/ledger FK references; <see cref="AuthUserId"/> maps it to the AuthHex
+/// <c>UserId</c> (GUID) and is JIT-provisioned on first authenticated request
+/// (docs/10 A.4/C.7). A seeded <c>system</c> user (id 1, null AuthUserId) is the
+/// fallback actor for unauthenticated/system operations. Model: docs/10 Part C.7.
+/// </summary>
+public class User
+{
+    /// <summary>Seeded fallback actor for unauthenticated/system operations.</summary>
+    public const long SystemUserId = 1;
+
+    public long UserId { get; set; }
+    public string Username { get; set; } = string.Empty;
+    public string DisplayName { get; set; } = string.Empty;
+    public EntityStatus Status { get; set; } = EntityStatus.Active;
+
+    /// <summary>AuthHex identity (token <c>UserId</c> GUID); null for the seeded system user.</summary>
+    public Guid? AuthUserId { get; set; }
+}

Backend/ERPCore/Domain/Entities/Vendor.cs

@@ -0,0 +1,25 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Vendor master (FR-MD-06). 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 Vendor
+{
+    public long VendorId { get; set; }
+    public string Code { get; set; } = string.Empty;
+    public string Name { get; set; } = string.Empty;
+    public string? Terms { get; set; }
+    public string? TaxReg { get; set; }
+    public string Currency { get; set; } = "LKR";
+    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/VendorQuotation.cs

@@ -0,0 +1,26 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// A vendor's quotation against an RFQ (FR-PROC-02). Per-item pricing lives in
+/// <see cref="Lines"/>.
+/// <para>
+/// Deviation note: docs/10 Part C.2 models <c>VENDOR_QUOTATION</c> with scalar
+/// <c>unit_price</c>/<c>lead_days</c> and no item reference, which cannot represent
+/// the per-line pricing the API contract requires (docs/11 §3.2). This header +
+/// <see cref="VendorQuotationLine"/> split follows the authoritative API shape.
+/// </para>
+/// </summary>
+public class VendorQuotation
+{
+    public long QuotationId { get; set; }
+
+    public long RfqId { get; set; }
+    public Rfq? Rfq { get; set; }
+
+    public long VendorId { get; set; }
+    public Vendor? Vendor { get; set; }
+
+    public DateTime CreatedAt { get; set; }
+
+    public ICollection<VendorQuotationLine> Lines { get; set; } = new List<VendorQuotationLine>();
+}

Backend/ERPCore/Domain/Entities/VendorQuotationLine.cs

@@ -0,0 +1,16 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>Per-item quoted price and lead time within a <see cref="VendorQuotation"/> (docs/11 §3.2).</summary>
+public class VendorQuotationLine
+{
+    public long QuotationLineId { get; set; }
+
+    public long QuotationId { get; set; }
+    public VendorQuotation? Quotation { get; set; }
+
+    public long ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public decimal UnitPrice { get; set; }
+    public int LeadDays { get; set; }
+}

Backend/ERPCore/Domain/Entities/Warehouse.cs

@@ -0,0 +1,14 @@
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Warehouse master (FR-MD-07, FR-WH-01). Owns a bin/location hierarchy.
+/// Model: docs/10-BACKEND-PHASE1.md Part C.1.
+/// </summary>
+public class Warehouse
+{
+    public long WarehouseId { get; set; }
+    public string Code { get; set; } = string.Empty;
+    public string Name { get; set; } = string.Empty;
+
+    public ICollection<Bin> Bins { get; set; } = new List<Bin>();
+}

Backend/ERPCore/Domain/Enums/AdjustmentStatus.cs

@@ -0,0 +1,13 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>
+/// Stock-adjustment lifecycle (docs/10 §B.8.1). Phase 1 auto-posts, so
+/// <see cref="PendingApproval"/> is reserved for the future threshold-approval
+/// workflow (FR-STK-07). Stored as a string.
+/// </summary>
+public enum AdjustmentStatus
+{
+    Draft,
+    PendingApproval,
+    Posted
+}

Backend/ERPCore/Domain/Enums/AuditAction.cs

@@ -0,0 +1,9 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>Kind of mutation recorded in the audit trail (FR-X-02). Stored as a string.</summary>
+public enum AuditAction
+{
+    Create,
+    Update,
+    Delete
+}

Backend/ERPCore/Domain/Enums/CountStatus.cs

@@ -0,0 +1,9 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>Stock-count lifecycle (docs/11 §8; docs/10 §B.8.1). Stored as a string.</summary>
+public enum CountStatus
+{
+    Draft,
+    Counted,
+    Posted
+}

Backend/ERPCore/Domain/Enums/CountType.cs

@@ -0,0 +1,8 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>Physical-count scope (docs/11 §8; FR-STK-08). Stored as a string.</summary>
+public enum CountType
+{
+    Cycle,
+    Full
+}

Backend/ERPCore/Domain/Enums/Direction.cs

@@ -0,0 +1,8 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>Stock-ledger movement direction (docs/11 §8). Stored as a string.</summary>
+public enum Direction
+{
+    In,
+    Out
+}

Backend/ERPCore/Domain/Enums/EntityStatus.cs

@@ -0,0 +1,12 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>
+/// Lifecycle status for deactivatable master data (Item, Vendor). Masters are
+/// never hard-deleted while referenced — they are set <see cref="Inactive"/>
+/// instead (FR-MD-08). Stored as a string.
+/// </summary>
+public enum EntityStatus
+{
+    Active,
+    Inactive
+}

Backend/ERPCore/Domain/Enums/GrnStatus.cs

@@ -0,0 +1,9 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>Goods-receipt-note lifecycle (docs/11 §8; docs/10 §B.8.1). Stored as a string.</summary>
+public enum GrnStatus
+{
+    Draft,
+    Confirmed,
+    Closed
+}

Backend/ERPCore/Domain/Enums/HoldStatus.cs

@@ -0,0 +1,12 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>
+/// Inspection-hold state of received stock (docs/11 §8; FR-GRN-05). <see cref="OnHold"/>
+/// stock is on-hand but not issuable until released (FR-WH-07). Stored as a string.
+/// </summary>
+public enum HoldStatus
+{
+    Available,
+    OnHold,
+    Rejected
+}

Backend/ERPCore/Domain/Enums/ItemType.cs

@@ -0,0 +1,12 @@
+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/PurchaseOrderStatus.cs

@@ -0,0 +1,17 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>
+/// Purchase-order lifecycle (docs/11 §8; docs/10 §B.8.1). Phase 1 auto-approves on
+/// creation, so <see cref="PendingApproval"/> is reserved (not entered) until the
+/// approval workflow is enabled (FR-PROC-04). Stored as a string.
+/// </summary>
+public enum PurchaseOrderStatus
+{
+    Draft,
+    PendingApproval,
+    Approved,
+    PartiallyReceived,
+    FullyReceived,
+    Closed,
+    Cancelled
+}

Backend/ERPCore/Domain/Enums/ReasonContext.cs

@@ -0,0 +1,9 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>Where a reason code applies (FR-X-04; docs/10 §B.8.3). Stored as a string.</summary>
+public enum ReasonContext
+{
+    Adjustment,
+    Return,
+    Count
+}

Backend/ERPCore/Domain/Enums/RequisitionStatus.cs

@@ -0,0 +1,8 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>Purchase-requisition lifecycle (docs/11 §3.1; docs/10 §B.8.1). Stored as a string.</summary>
+public enum RequisitionStatus
+{
+    Draft,
+    Submitted
+}

Backend/ERPCore/Domain/Enums/ReturnStatus.cs

@@ -0,0 +1,8 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>Purchase-return lifecycle (docs/11 §3.4). Auto-posts in Phase 1. Stored as a string.</summary>
+public enum ReturnStatus
+{
+    Draft,
+    Posted
+}

Backend/ERPCore/Domain/Enums/RfqStatus.cs

@@ -0,0 +1,8 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>RFQ lifecycle (docs/11 §3.2). Stored as a string.</summary>
+public enum RfqStatus
+{
+    Open,
+    Closed
+}

Backend/ERPCore/Domain/Enums/TrackingMode.cs

@@ -0,0 +1,12 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>
+/// How on-hand units of an item are individually tracked (FR-MD-01). Values match
+/// the <c>trackingMode</c> enum in docs/11-BACKEND-PHASE1.md §8. Stored as a string.
+/// </summary>
+public enum TrackingMode
+{
+    None,
+    Batch,
+    Serial
+}

Backend/ERPCore/Domain/Enums/TransferStatus.cs

@@ -0,0 +1,10 @@
+namespace ERPCore.Domain.Enums;
+
+/// <summary>Stock-transfer lifecycle (docs/11 §8; docs/10 §B.8.1). Stored as a string.</summary>
+public enum TransferStatus
+{
+    Draft,
+    InTransit,
+    Received,
+    Closed
+}

Backend/ERPCore/Dtos/Audit/AuditDtos.cs

@@ -0,0 +1,12 @@
+using System.Text.Json;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Audit;
+
+/// <summary>An audit-trail entry (FR-X-02). <c>ChangeSet</c> is the stored JSON, inlined.</summary>
+public sealed record AuditLogDto(
+    long AuditId, long UserId, string EntityType, long EntityId, AuditAction Action, JsonElement ChangeSet, DateTime CreatedAt);
+
+/// <summary>A GL-ready journal stub emitted per stock movement (FR-STK-13).</summary>
+public sealed record JournalEntryStubDto(
+    long JournalId, string SourceDocType, long SourceDocId, string DebitAccount, string CreditAccount, decimal Amount);

Backend/ERPCore/Dtos/Categories/CategoryDtos.cs

@@ -0,0 +1,15 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace ERPCore.Dtos.Categories;
+
+/// <summary>Flat category resource (docs/11-BACKEND-PHASE1.md §2.3).</summary>
+public sealed record CategoryDto(long CategoryId, string Name, long? ParentId);
+
+/// <summary>Nested category node for <c>GET /categories?tree=true</c>.</summary>
+public sealed record CategoryTreeDto(long CategoryId, string Name, long? ParentId, IReadOnlyList<CategoryTreeDto> Children);
+
+public sealed class CreateCategoryRequest
+{
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+    public long? ParentId { get; set; }
+}

Backend/ERPCore/Dtos/Common/PageQuery.cs

@@ -0,0 +1,37 @@
+namespace ERPCore.Dtos.Common;
+
+/// <summary>
+/// Shared paging/sorting query binding (docs/11-BACKEND-PHASE1.md §1.5). Page size
+/// is clamped to <see cref="MaxPageSize"/> to enforce pagination bounds
+/// (02-SECURITY B.6). Bind from the query string on list endpoints.
+/// </summary>
+public class PageQuery
+{
+    public const int MaxPageSize = 200;
+    public const int DefaultPageSize = 20;
+
+    private int _page = 1;
+    private int _pageSize = DefaultPageSize;
+
+    /// <summary>1-based page number (default 1).</summary>
+    public int Page
+    {
+        get => _page;
+        set => _page = value < 1 ? 1 : value;
+    }
+
+    /// <summary>Page size (default 20, clamped to 1..200).</summary>
+    public int PageSize
+    {
+        get => _pageSize;
+        set => _pageSize = value < 1 ? DefaultPageSize : Math.Min(value, MaxPageSize);
+    }
+
+    /// <summary>Free-text search term (<c>q</c>).</summary>
+    public string? Q { get; set; }
+
+    /// <summary>Sort spec, e.g. <c>name</c> or <c>-createdAt</c>.</summary>
+    public string? Sort { get; set; }
+
+    public int Skip => (Page - 1) * PageSize;
+}

Backend/ERPCore/Dtos/Common/PagedResponse.cs

@@ -0,0 +1,17 @@
+namespace ERPCore.Dtos.Common;
+
+/// <summary>
+/// List envelope matching docs/11-BACKEND-PHASE1.md §1.4:
+/// <c>{ "items": [...], "pagination": { page, pageSize, totalItems, totalPages } }</c>.
+/// </summary>
+public sealed record PagedResponse<T>(IReadOnlyList<T> Items, PaginationDto Pagination)
+{
+    public static PagedResponse<T> Create(IReadOnlyList<T> items, int page, int pageSize, int totalItems)
+    {
+        var totalPages = pageSize <= 0 ? 0 : (int)Math.Ceiling(totalItems / (double)pageSize);
+        return new PagedResponse<T>(items, new PaginationDto(page, pageSize, totalItems, totalPages));
+    }
+}
+
+/// <summary>Pagination metadata block (docs/11 §1.4).</summary>
+public sealed record PaginationDto(int Page, int PageSize, int TotalItems, int TotalPages);

Backend/ERPCore/Dtos/Grn/GrnDtos.cs

@@ -0,0 +1,63 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Grn;
+
+// Responses (docs/11 §4) --------------------------------------------------------
+
+public sealed record GrnLineDto(
+    long GrnLineId, long? PoLineId, long ItemId, long UomId, long? BinId,
+    decimal Qty, decimal UnitCost, decimal ReceivedValue, HoldStatus HoldStatus, long? BatchId);
+
+public sealed record GrnDto(
+    long GrnId, string DocNo, long? PoId, long VendorId, long WarehouseId, GrnStatus Status,
+    long CreatedBy, DateTime CreatedAt, DateTime? PostedAt, IReadOnlyList<GrnLineDto> Lines);
+
+public sealed record CreatedLayerDto(
+    long LayerId, long ItemId, long WarehouseId, long? BatchId,
+    decimal QtyReceived, decimal QtyRemaining, decimal UnitCost, DateTime ReceiptDate);
+
+public sealed record GrnConfirmResultDto(
+    long GrnId, GrnStatus Status, DateTime PostedAt,
+    IReadOnlyList<CreatedLayerDto> CreatedLayers, IReadOnlyList<long> LedgerRefs, PurchaseOrderStatus? PoStatus);
+
+public sealed record ReleaseLineResultDto(long GrnLineId, HoldStatus HoldStatus);
+
+// Requests ----------------------------------------------------------------------
+
+public sealed class BatchInput
+{
+    [Required, StringLength(50)] public string BatchNo { get; set; } = string.Empty;
+    public DateOnly? ExpiryDate { get; set; }
+}
+
+public sealed class CreateGrnLineInput
+{
+    /// <summary>Set for a PO-based receipt; cost is then derived from the PO line (02-SECURITY C.3).</summary>
+    public long? PoLineId { get; set; }
+    [Required] public long ItemId { get; set; }
+    [Required] public long UomId { get; set; }
+    public long? BinId { get; set; }
+    [Range(0.0001, double.MaxValue)] public decimal Qty { get; set; }
+    /// <summary>Used only for direct (no-PO) receipts; ignored when <see cref="PoLineId"/> is set.</summary>
+    [Range(0, double.MaxValue)] public decimal UnitCost { get; set; }
+    [EnumDataType(typeof(HoldStatus))] public HoldStatus HoldStatus { get; set; } = HoldStatus.Available;
+    public BatchInput? Batch { get; set; }
+}
+
+public sealed class CreateGrnRequest
+{
+    /// <summary>PO to receive against; null for a direct/emergency receipt (FR-GRN-02).</summary>
+    public long? PoId { get; set; }
+    /// <summary>Required for a direct receipt (no PO); ignored otherwise (vendor derives from the PO).</summary>
+    public long? VendorId { get; set; }
+    [Required] public long WarehouseId { get; set; }
+    [Required, MinLength(1)] public List<CreateGrnLineInput> Lines { get; set; } = new();
+}
+
+public sealed class ReleaseLineRequest
+{
+    /// <summary><c>Release</c> makes the stock available; <c>Reject</c> removes it from on-hand.</summary>
+    [Required, RegularExpression("Release|Reject")]
+    public string Action { get; set; } = "Release";
+}

Backend/ERPCore/Dtos/Items/ItemDtos.cs

@@ -0,0 +1,89 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Items;
+
+// Response DTOs (docs/11-BACKEND-PHASE1.md §2.1) --------------------------------
+
+/// <summary>Row shape for <c>GET /items</c>.</summary>
+public sealed record ItemListItemDto(
+    long ItemId, string Sku, string Name, long CategoryId, long BaseUomId,
+    long? DefaultVendorId, ItemType ItemType, TrackingMode TrackingMode,
+    string? TaxClass, EntityStatus Status);
+
+/// <summary>A single per-warehouse reorder policy row.</summary>
+public sealed record ItemReorderDto(long WarehouseId, decimal ReorderPoint, decimal ReorderQty);
+
+/// <summary>Full item resource for <c>GET /items/{id}</c> and create/update responses.</summary>
+public sealed record ItemDetailDto(
+    long ItemId, string Sku, string Name, string? Description, long CategoryId,
+    long BaseUomId, long? DefaultVendorId, ItemType ItemType, TrackingMode TrackingMode,
+    string? TaxClass, EntityStatus Status, IReadOnlyList<ItemReorderDto> Reorder,
+    DateTime CreatedAt, DateTime? UpdatedAt);
+
+/// <summary>UOM conversion row (docs/11 §2.2).</summary>
+public sealed record UomConversionDto(long ConversionId, long FromUom, long ToUom, decimal Factor);
+
+/// <summary>Response body for <c>PUT /items/{id}/uom-conversions</c>.</summary>
+public sealed record ItemUomConversionsDto(long ItemId, long BaseUomId, IReadOnlyList<UomConversionDto> Conversions);
+
+/// <summary>Response body for <c>PUT /items/{id}/reorder</c>.</summary>
+public sealed record ItemReorderSettingsDto(IReadOnlyList<ItemReorderDto> Settings);
+
+// 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 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 long CategoryId { get; set; }
+    [Required] public long BaseUomId { get; set; }
+    public long? DefaultVendorId { get; set; }
+    [Required, EnumDataType(typeof(ItemType))] public ItemType ItemType { get; set; }
+    [EnumDataType(typeof(TrackingMode))] public TrackingMode TrackingMode { get; set; } = TrackingMode.None;
+    [StringLength(20)] public string? TaxClass { get; set; }
+}
+
+public sealed class UpdateItemRequest
+{
+    [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 long CategoryId { get; set; }
+    [Required] public long BaseUomId { get; set; }
+    public long? DefaultVendorId { get; set; }
+    [Required, EnumDataType(typeof(ItemType))] public ItemType ItemType { get; set; }
+    [EnumDataType(typeof(TrackingMode))] public TrackingMode TrackingMode { get; set; } = TrackingMode.None;
+    [StringLength(20)] public string? TaxClass { get; set; }
+}
+
+public sealed class UpdateItemStatusRequest
+{
+    [Required, EnumDataType(typeof(EntityStatus))] public EntityStatus Status { get; set; }
+}
+
+public sealed class ReorderSettingInput
+{
+    [Required] public long WarehouseId { get; set; }
+    [Range(0, double.MaxValue)] public decimal ReorderPoint { get; set; }
+    [Range(0, double.MaxValue)] public decimal ReorderQty { get; set; }
+}
+
+public sealed class UpdateReorderRequest
+{
+    [Required, MinLength(1)] public List<ReorderSettingInput> Settings { get; set; } = new();
+}
+
+public sealed class UomConversionInput
+{
+    [Required] public long FromUom { get; set; }
+    [Required] public long ToUom { get; set; }
+    [Range(0.000001, double.MaxValue)] public decimal Factor { get; set; }
+}
+
+public sealed class UpdateUomConversionsRequest
+{
+    [Required, MinLength(1)] public List<UomConversionInput> Conversions { get; set; } = new();
+}

Backend/ERPCore/Dtos/Procurement/PurchaseOrderDtos.cs

@@ -0,0 +1,52 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Procurement;
+
+// Responses (docs/11 §3.3) ------------------------------------------------------
+
+public sealed record PoLineDto(
+    long PoLineId, long ItemId, long UomId, long WarehouseId,
+    decimal Qty, decimal UnitPrice, decimal Tax, decimal QtyReceived);
+
+public sealed record PoTotalsDto(decimal SubTotal, decimal Tax, decimal GrandTotal, string Currency);
+
+public sealed record PurchaseOrderDto(
+    long PoId, string DocNo, long VendorId, long? RequisitionId, PurchaseOrderStatus Status,
+    bool ApprovalRequired, long CreatedBy, DateTime CreatedAt, DateTime? UpdatedAt,
+    PoTotalsDto Totals, IReadOnlyList<PoLineDto> Lines);
+
+public sealed record PurchaseOrderSummaryDto(
+    long PoId, string DocNo, long VendorId, PurchaseOrderStatus Status,
+    bool ApprovalRequired, DateTime CreatedAt, PoTotalsDto Totals);
+
+// Requests — server sets docNo, status, createdBy, timestamps, qtyReceived, totals
+
+public sealed class CreatePoLineInput
+{
+    [Required] public long ItemId { get; set; }
+    [Required] public long UomId { get; set; }
+    [Required] public long WarehouseId { get; set; }
+    [Range(0.0001, double.MaxValue)] public decimal Qty { get; set; }
+    [Range(0, double.MaxValue)] public decimal UnitPrice { get; set; }
+    [Range(0, 1)] public decimal Tax { get; set; }
+}
+
+public sealed class CreatePurchaseOrderRequest
+{
+    [Required] public long VendorId { get; set; }
+    public long? RequisitionId { get; set; }
+    [Required, MinLength(1)] public List<CreatePoLineInput> Lines { get; set; } = new();
+}
+
+public sealed class UpdatePurchaseOrderRequest
+{
+    [Required] public long VendorId { get; set; }
+    public long? RequisitionId { get; set; }
+    [Required, MinLength(1)] public List<CreatePoLineInput> Lines { get; set; } = new();
+}
+
+public sealed class CancelPurchaseOrderRequest
+{
+    [StringLength(500)] public string? Reason { get; set; }
+}

Backend/ERPCore/Dtos/Procurement/PurchaseReturnDtos.cs

@@ -0,0 +1,31 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Procurement;
+
+// Responses (docs/11 §3.4) ------------------------------------------------------
+
+public sealed record PurchaseReturnLineDto(long ReturnLineId, long? GrnLineId, long ItemId, decimal Qty);
+
+public sealed record PurchaseReturnDto(
+    long ReturnId, string DocNo, long VendorId, long WarehouseId, long ReasonCodeId, ReturnStatus Status,
+    long CreatedBy, IReadOnlyList<PurchaseReturnLineDto> Lines, IReadOnlyList<long> LedgerRefs);
+
+// Requests ----------------------------------------------------------------------
+
+public sealed class CreatePurchaseReturnLineInput
+{
+    /// <summary>Original GRN line, for traceability against the receipt.</summary>
+    public long? GrnLineId { get; set; }
+    [Required] public long ItemId { get; set; }
+    [Range(0.0001, double.MaxValue)] public decimal Qty { get; set; }
+}
+
+public sealed class CreatePurchaseReturnRequest
+{
+    [Required] public long VendorId { get; set; }
+    [Required] public long WarehouseId { get; set; }
+    /// <summary>Nullable so an omitted value is a distinct <c>REASON_CODE_REQUIRED</c> error.</summary>
+    public long? ReasonCodeId { get; set; }
+    [Required, MinLength(1)] public List<CreatePurchaseReturnLineInput> Lines { get; set; } = new();
+}

Backend/ERPCore/Dtos/Procurement/RequisitionDtos.cs

@@ -0,0 +1,29 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Procurement;
+
+// Responses (docs/11 §3.1) ------------------------------------------------------
+
+public sealed record RequisitionLineDto(long ReqLineId, long ItemId, decimal Qty, DateOnly? RequiredBy);
+
+public sealed record RequisitionDto(
+    long RequisitionId, string DocNo, RequisitionStatus Status, long RequestedBy,
+    DateTime CreatedAt, IReadOnlyList<RequisitionLineDto> Lines);
+
+public sealed record RequisitionSummaryDto(
+    long RequisitionId, string DocNo, RequisitionStatus Status, long RequestedBy, DateTime CreatedAt);
+
+// Requests — server sets docNo, status, requestedBy (audit actor), timestamps ----
+
+public sealed class CreateRequisitionLineInput
+{
+    [Required] public long ItemId { get; set; }
+    [Range(0.0001, double.MaxValue)] public decimal Qty { get; set; }
+    public DateOnly? RequiredBy { get; set; }
+}
+
+public sealed class CreateRequisitionRequest
+{
+    [Required, MinLength(1)] public List<CreateRequisitionLineInput> Lines { get; set; } = new();
+}

Backend/ERPCore/Dtos/Procurement/RfqDtos.cs

@@ -0,0 +1,50 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Procurement;
+
+// Responses (docs/11 §3.2) ------------------------------------------------------
+
+public sealed record RfqLineDto(long RfqLineId, long ItemId, decimal Qty);
+
+public sealed record RfqDto(
+    long RfqId, string DocNo, long RequisitionId, RfqStatus Status, IReadOnlyList<RfqLineDto> Lines);
+
+public sealed record QuotationLineDto(long ItemId, decimal UnitPrice, int LeadDays);
+
+public sealed record VendorQuotationDto(
+    long QuotationId, long RfqId, long VendorId, IReadOnlyList<QuotationLineDto> Lines);
+
+/// <summary>Per-item, per-vendor price matrix for <c>GET /rfqs/{id}/comparison</c>.</summary>
+public sealed record RfqComparisonCellDto(long VendorId, long QuotationId, decimal UnitPrice, int LeadDays);
+public sealed record RfqComparisonRowDto(long ItemId, decimal Qty, IReadOnlyList<RfqComparisonCellDto> Quotes);
+public sealed record RfqComparisonDto(long RfqId, IReadOnlyList<long> VendorIds, IReadOnlyList<RfqComparisonRowDto> Rows);
+
+// Requests ----------------------------------------------------------------------
+
+public sealed class CreateRfqLineInput
+{
+    [Required] public long ItemId { get; set; }
+    [Range(0.0001, double.MaxValue)] public decimal Qty { get; set; }
+}
+
+public sealed class CreateRfqRequest
+{
+    [Required] public long RequisitionId { get; set; }
+    /// <summary>Vendors the RFQ is issued to (validated for existence; quotations reference them).</summary>
+    public List<long> VendorIds { get; set; } = new();
+    [Required, MinLength(1)] public List<CreateRfqLineInput> Lines { get; set; } = new();
+}
+
+public sealed class CreateQuotationLineInput
+{
+    [Required] public long ItemId { get; set; }
+    [Range(0, double.MaxValue)] public decimal UnitPrice { get; set; }
+    [Range(0, int.MaxValue)] public int LeadDays { get; set; }
+}
+
+public sealed class CreateQuotationRequest
+{
+    [Required] public long VendorId { get; set; }
+    [Required, MinLength(1)] public List<CreateQuotationLineInput> Lines { get; set; } = new();
+}

Backend/ERPCore/Dtos/Reference/ReasonCodeDtos.cs

@@ -0,0 +1,14 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Reference;
+
+/// <summary>Reason code (docs/11 §6).</summary>
+public sealed record ReasonCodeDto(long ReasonCodeId, string Code, string Description, ReasonContext Context);
+
+public sealed class CreateReasonCodeRequest
+{
+    [Required, StringLength(20)] public string Code { get; set; } = string.Empty;
+    [Required, StringLength(200)] public string Description { get; set; } = string.Empty;
+    [Required, EnumDataType(typeof(ReasonContext))] public ReasonContext Context { get; set; }
+}

Backend/ERPCore/Dtos/Stock/AdjustmentDtos.cs

@@ -0,0 +1,31 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Stock;
+
+// Responses (docs/11 §5.5) ------------------------------------------------------
+
+public sealed record AdjustmentLineDto(long AdjLineId, long ItemId, long? BinId, long? BatchId, decimal QtyDelta);
+
+public sealed record AdjustmentDto(
+    long AdjustmentId, string DocNo, long WarehouseId, long ReasonCodeId, AdjustmentStatus Status,
+    long CreatedBy, DateTime CreatedAt, IReadOnlyList<AdjustmentLineDto> Lines, IReadOnlyList<long> LedgerRefs);
+
+// Requests ----------------------------------------------------------------------
+
+public sealed class CreateAdjustmentLineInput
+{
+    [Required] public long ItemId { get; set; }
+    public long? BinId { get; set; }
+    public long? BatchId { get; set; }
+    /// <summary>Signed base-UOM delta: negative consumes FIFO layers, positive adds stock.</summary>
+    public decimal QtyDelta { get; set; }
+}
+
+public sealed class CreateAdjustmentRequest
+{
+    [Required] public long WarehouseId { get; set; }
+    /// <summary>Nullable so an omitted value is a distinct <c>REASON_CODE_REQUIRED</c> error, not 0.</summary>
+    public long? ReasonCodeId { get; set; }
+    [Required, MinLength(1)] public List<CreateAdjustmentLineInput> Lines { get; set; } = new();
+}

Backend/ERPCore/Dtos/Stock/CountDtos.cs

@@ -0,0 +1,33 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Stock;
+
+// Responses (docs/11 §5.6) ------------------------------------------------------
+
+public sealed record CountLineDto(long CountLineId, long ItemId, long? BinId, decimal SystemQty, decimal? CountedQty, decimal? Variance);
+
+public sealed record CountDto(
+    long CountId, string DocNo, long WarehouseId, CountType CountType, CountStatus Status, IReadOnlyList<CountLineDto> Lines);
+
+public sealed record CountPostResultDto(long CountId, CountStatus Status, long? AdjustmentId, IReadOnlyList<long> LedgerRefs);
+
+// Requests ----------------------------------------------------------------------
+
+public sealed class CreateCountRequest
+{
+    [Required] public long WarehouseId { get; set; }
+    [Required, EnumDataType(typeof(CountType))] public CountType CountType { get; set; }
+    [Required, MinLength(1)] public List<long> ItemIds { get; set; } = new();
+}
+
+public sealed class EnterCountLineInput
+{
+    [Required] public long CountLineId { get; set; }
+    [Range(0, double.MaxValue)] public decimal CountedQty { get; set; }
+}
+
+public sealed class EnterCountsRequest
+{
+    [Required, MinLength(1)] public List<EnterCountLineInput> Lines { get; set; } = new();
+}

Backend/ERPCore/Dtos/Stock/ReorderDtos.cs

@@ -0,0 +1,6 @@
+namespace ERPCore.Dtos.Stock;
+
+/// <summary>An item at/below its reorder point (docs/11 §5.7; FR-STK-10). Computed on read.</summary>
+public sealed record ReorderAlertDto(
+    long ItemId, long WarehouseId, decimal Available,
+    decimal ReorderPoint, decimal ReorderQty, decimal SuggestedRequisitionQty);

Backend/ERPCore/Dtos/Stock/StockDtos.cs

@@ -0,0 +1,22 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Stock;
+
+/// <summary>Stock enquiry (docs/11 §5.1). available = onHand − onHold − reserved − inTransit(out).</summary>
+public sealed record StockOnHandDto(
+    long ItemId, long WarehouseId, decimal OnHand, decimal Available,
+    decimal OnHold, decimal InTransit, decimal Reserved, DateTime AsOf);
+
+/// <summary>A stock-ledger row (docs/11 §5.2).</summary>
+public sealed record StockLedgerRowDto(
+    long LedgerId, long ItemId, long WarehouseId, long? BinId, long? BatchId, long? SerialId,
+    Direction Direction, decimal QtyBase, decimal UnitCost, decimal Value, decimal RunningBalance,
+    string SourceDocType, long SourceDocId, long UserId, DateTime CreatedAt);
+
+/// <summary>An open FIFO layer in a valuation (docs/11 §5.3).</summary>
+public sealed record StockValuationLayerDto(long LayerId, decimal QtyRemaining, decimal UnitCost, decimal Value, DateTime ReceiptDate);
+
+/// <summary>Valuation of on-hand stock from open FIFO layers (docs/11 §5.3).</summary>
+public sealed record StockValuationDto(
+    long ItemId, long WarehouseId, IReadOnlyList<StockValuationLayerDto> Layers,
+    decimal TotalQty, decimal TotalValue, string Currency, string CostingMethod);

Backend/ERPCore/Dtos/Stock/TransferDtos.cs

@@ -0,0 +1,52 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Stock;
+
+// Responses (docs/11 §5.4) ------------------------------------------------------
+
+public sealed record TransferLineDto(
+    long TransferLineId, long ItemId, long? SrcBinId, long? DestBinId, long? BatchId, decimal Qty, decimal QtyReceived);
+
+public sealed record TransferDto(
+    long TransferId, string DocNo, long SrcWarehouseId, long DestWarehouseId,
+    TransferStatus Status, IReadOnlyList<TransferLineDto> Lines);
+
+public sealed record ConsumedLayerDto(long LayerId, decimal QtyConsumed, decimal UnitCost);
+
+public sealed record DispatchResultDto(
+    long TransferId, TransferStatus Status, IReadOnlyList<ConsumedLayerDto> ConsumedLayers, IReadOnlyList<long> LedgerRefs);
+
+public sealed record TransferCreatedLayerDto(long LayerId, long WarehouseId, decimal QtyReceived, decimal UnitCost);
+
+public sealed record ReceiveResultDto(
+    long TransferId, TransferStatus Status, IReadOnlyList<TransferCreatedLayerDto> CreatedLayers, IReadOnlyList<long> LedgerRefs);
+
+// Requests ----------------------------------------------------------------------
+
+public sealed class CreateTransferLineInput
+{
+    [Required] public long ItemId { get; set; }
+    public long? SrcBinId { get; set; }
+    public long? DestBinId { get; set; }
+    public long? BatchId { get; set; }
+    [Range(0.0001, double.MaxValue)] public decimal Qty { get; set; }
+}
+
+public sealed class CreateTransferRequest
+{
+    [Required] public long SrcWarehouseId { get; set; }
+    [Required] public long DestWarehouseId { get; set; }
+    [Required, MinLength(1)] public List<CreateTransferLineInput> Lines { get; set; } = new();
+}
+
+public sealed class ReceiveTransferLineInput
+{
+    [Required] public long TransferLineId { get; set; }
+    [Range(0.0001, double.MaxValue)] public decimal Qty { get; set; }
+}
+
+public sealed class ReceiveTransferRequest
+{
+    [Required, MinLength(1)] public List<ReceiveTransferLineInput> Lines { get; set; } = new();
+}

Backend/ERPCore/Dtos/Uoms/UomDtos.cs

@@ -0,0 +1,11 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace ERPCore.Dtos.Uoms;
+
+/// <summary>UOM resource (docs/11-BACKEND-PHASE1.md §2.2).</summary>
+public sealed record UomDto(long UomId, string Name);
+
+public sealed class CreateUomRequest
+{
+    [Required, StringLength(50)] public string Name { get; set; } = string.Empty;
+}

Backend/ERPCore/Dtos/Vendors/VendorDtos.cs

@@ -0,0 +1,32 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Vendors;
+
+/// <summary>Vendor resource (docs/11-BACKEND-PHASE1.md §2.4).</summary>
+public sealed record VendorDto(
+    long VendorId, string Code, string Name, string? Terms, string? TaxReg,
+    string Currency, EntityStatus Status, DateTime CreatedAt, DateTime? UpdatedAt);
+
+public sealed class CreateVendorRequest
+{
+    [Required, StringLength(50)] public string Code { get; set; } = string.Empty;
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+    [StringLength(50)] public string? Terms { get; set; }
+    [StringLength(50)] public string? TaxReg { get; set; }
+    [Required, StringLength(3, MinimumLength = 3)] public string Currency { get; set; } = "LKR";
+}
+
+public sealed class UpdateVendorRequest
+{
+    [Required, StringLength(50)] public string Code { get; set; } = string.Empty;
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+    [StringLength(50)] public string? Terms { get; set; }
+    [StringLength(50)] public string? TaxReg { get; set; }
+    [Required, StringLength(3, MinimumLength = 3)] public string Currency { get; set; } = "LKR";
+}
+
+public sealed class UpdateVendorStatusRequest
+{
+    [Required, EnumDataType(typeof(EntityStatus))] public EntityStatus Status { get; set; }
+}

Backend/ERPCore/Dtos/Warehouses/WarehouseDtos.cs

@@ -0,0 +1,21 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace ERPCore.Dtos.Warehouses;
+
+/// <summary>Warehouse resource (docs/11-BACKEND-PHASE1.md §2.5).</summary>
+public sealed record WarehouseDto(long WarehouseId, string Code, string Name);
+
+/// <summary>Bin/location resource (docs/11 §2.5).</summary>
+public sealed record BinDto(long BinId, long WarehouseId, string Code, string? BinType);
+
+public sealed class CreateWarehouseRequest
+{
+    [Required, StringLength(50)] public string Code { get; set; } = string.Empty;
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+}
+
+public sealed class CreateBinRequest
+{
+    [Required, StringLength(50)] public string Code { get; set; } = string.Empty;
+    [StringLength(50)] public string? BinType { get; set; }
+}

Backend/ERPCore/Infra/Auth/AuthHexClaims.cs

@@ -0,0 +1,17 @@
+namespace ERPCore.Infra.Auth;
+
+/// <summary>
+/// Claim type names emitted by the AuthHex IdP (see its <c>JwtTokenHelper</c>).
+/// AuthHex uses no standard <c>sub</c>/<c>nameid</c>; identity is the custom
+/// <see cref="UserId"/> (GUID). These are read verbatim (JWT bearer is configured
+/// with <c>MapInboundClaims = false</c>).
+/// </summary>
+public static class AuthHexClaims
+{
+    public const string UserId = "UserId";
+    public const string UserTypeId = "UserTypeId";
+    public const string UserTypeCode = "UserTypeCode";
+    public const string RoleId = "RoleId";
+    public const string RoleCode = "RoleCode";
+    public const string Nic = "NIC";
+}

Backend/ERPCore/Infra/Auth/CurrentUser.cs

@@ -1,4 +1,5 @@
 using System.Security.Claims;
+using ERPCore.Domain.Entities;
 
 namespace ERPCore.Infra.Auth;
 
@@ -28,4 +29,6 @@ public sealed class CurrentUser : ICurrentUser
             return string.IsNullOrWhiteSpace(sub) ? SystemActor : sub;
         }
     }
+
+    public long AuditUserId => long.TryParse(UserId, out var id) ? id : User.SystemUserId;
 }

Backend/ERPCore/Infra/Auth/ICurrentUser.cs

@@ -10,6 +10,13 @@ public interface ICurrentUser
     /// <summary>The audit actor identity (token `sub`), or "system" when unauthenticated.</summary>
     string UserId { get; }
 
+    /// <summary>
+    /// Numeric audit actor for stamping document <c>createdBy</c>/<c>requestedBy</c> FKs.
+    /// Resolves the token <c>sub</c> to a user id; falls back to the seeded system
+    /// user (<see cref="Entities.User.SystemUserId"/>) while auth is deferred (§6).
+    /// </summary>
+    long AuditUserId { get; }
+
     /// <summary>True when the request carries an authenticated principal.</summary>
     bool IsAuthenticated { get; }
 }

Backend/ERPCore/Infra/Auth/JwtAuthExtensions.cs

@@ -1,25 +1,42 @@
-using System.Text;
+using System.Security.Cryptography;
 using Microsoft.AspNetCore.Authentication.JwtBearer;
 using Microsoft.IdentityModel.Tokens;
 
 namespace ERPCore.Infra.Auth;
 
 /// <summary>
-/// JWT bearer wiring. Authentication only — RBAC/authorization policies are
-/// deferred for Phase 1; the validated principal exists solely so that
-/// <see cref="ICurrentUser"/> can stamp the audit actor.
+/// Auth wiring for ERPCore as a **resource server** for the external AuthHex IdP
+/// (docs/10 A.4). Validates AuthHex's **RS256** tokens against AuthHex's RSA public
+/// key (configured statically — no JWKS), issuer <c>AuthHex</c>, audience
+/// <c>AuthHexClient</c>. A single door policy (<see cref="ErpAccessPolicy"/>) admits
+/// only ERP <c>UserType</c>/<c>Role</c> holders when those codes are configured;
+/// per-endpoint RBAC stays deferred. Identity → audit actor is resolved by
+/// <see cref="ShadowUserClaimsTransformation"/> + <see cref="ICurrentUser"/>.
 /// </summary>
 public static class JwtAuthExtensions
 {
+    /// <summary>Authorization policy applied to every v1 controller (via ApiControllerBase).</summary>
+    public const string ErpAccessPolicy = "ErpAccess";
+
     public static IServiceCollection AddErpJwtAuth(this IServiceCollection services, IConfiguration config)
     {
-        var issuer = config["Jwt:Issuer"];
-        var audience = config["Jwt:Audience"];
-        var signingKey = config["Jwt:SigningKey"] ?? string.Empty;
+        var issuer = config["Auth:Issuer"];
+        var audience = config["Auth:Audience"];
+        var publicKeyXml = config["Auth:RsaPublicKeyXml"]
+            ?? throw new InvalidOperationException("Auth:RsaPublicKeyXml (AuthHex RSA public key) is not configured.");
+        var requiredUserType = config["Auth:RequiredUserTypeCode"];
+        var requiredRole = config["Auth:RequiredRoleCode"];
+
+        // AuthHex publishes no JWKS; the RSA public key is configured statically.
+        var rsa = RSA.Create();
+        rsa.FromXmlString(publicKeyXml);
+        var signingKey = new RsaSecurityKey(rsa);
 
         services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
             .AddJwtBearer(options =>
             {
+                // Keep AuthHex's claim names verbatim (UserId, UserTypeCode, RoleCode …).
+                options.MapInboundClaims = false;
                 options.TokenValidationParameters = new TokenValidationParameters
                 {
                     ValidateIssuer = true,
@@ -28,12 +45,26 @@ public static class JwtAuthExtensions
                     ValidAudience = audience,
                     ValidateLifetime = true,
                     ValidateIssuerSigningKey = true,
-                    IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(signingKey)),
+                    IssuerSigningKey = signingKey,
+                    ValidAlgorithms = new[] { SecurityAlgorithms.RsaSha256 },
                     ClockSkew = TimeSpan.FromSeconds(30)
                 };
             });
 
-        services.AddAuthorization();
+        services.AddAuthorization(options =>
+        {
+            options.AddPolicy(ErpAccessPolicy, policy =>
+            {
+                policy.RequireAuthenticatedUser();
+                // Door gate: only enforce a UserType/Role when configured (AuthHex is a
+                // shared IdP). Empty config = require a valid ERP token only.
+                if (!string.IsNullOrWhiteSpace(requiredUserType))
+                    policy.RequireClaim(AuthHexClaims.UserTypeCode, requiredUserType);
+                if (!string.IsNullOrWhiteSpace(requiredRole))
+                    policy.RequireClaim(AuthHexClaims.RoleCode, requiredRole);
+            });
+        });
+
         return services;
     }
 }

Backend/ERPCore/Infra/Auth/ShadowUserClaimsTransformation.cs

@@ -0,0 +1,76 @@
+using System.Security.Claims;
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using ERPCore.Infra.Persistence;
+using Microsoft.AspNetCore.Authentication;
+using Microsoft.EntityFrameworkCore;
+
+namespace ERPCore.Infra.Auth;
+
+/// <summary>
+/// Maps an authenticated AuthHex principal to ERPCore's local identity (docs/10 A.4/A.5).
+/// AuthHex tokens carry the user as a custom <c>UserId</c> (GUID) claim and no
+/// <c>sub</c>/<c>nameid</c>. This transformation JIT-provisions a local shadow
+/// <see cref="User"/> (keyed by <c>auth_user_id</c>) and injects the local
+/// <c>long</c> id as <see cref="ClaimTypes.NameIdentifier"/>, so
+/// <see cref="ICurrentUser"/>/<c>AuditUserId</c> resolve the real user unchanged.
+/// Idempotent — <see cref="IClaimsTransformation"/> may run several times per request.
+/// </summary>
+public sealed class ShadowUserClaimsTransformation : IClaimsTransformation
+{
+    private readonly ErpDbContext _db;
+
+    public ShadowUserClaimsTransformation(ErpDbContext db) => _db = db;
+
+    public async Task<ClaimsPrincipal> TransformAsync(ClaimsPrincipal principal)
+    {
+        if (principal.Identity is not ClaimsIdentity identity || !identity.IsAuthenticated)
+            return principal;
+        if (identity.HasClaim(c => c.Type == ClaimTypes.NameIdentifier))
+            return principal; // already resolved this request
+
+        var raw = principal.FindFirstValue(AuthHexClaims.UserId);
+        if (!Guid.TryParse(raw, out var authUserId))
+            return principal; // no mappable identity → CurrentUser falls back to system
+
+        var nic = principal.FindFirstValue(AuthHexClaims.Nic);
+        var localId = await ResolveOrProvisionAsync(authUserId, nic);
+
+        identity.AddClaim(new Claim(ClaimTypes.NameIdentifier, localId.ToString()));
+        return principal;
+    }
+
+    private async Task<long> ResolveOrProvisionAsync(Guid authUserId, string? nic)
+    {
+        var existing = await _db.Users.AsNoTracking()
+            .Where(u => u.AuthUserId == authUserId)
+            .Select(u => u.UserId)
+            .FirstOrDefaultAsync();
+        if (existing != 0) return existing;
+
+        var label = string.IsNullOrWhiteSpace(nic) ? authUserId.ToString() : nic.Trim();
+        var user = new User
+        {
+            AuthUserId = authUserId,
+            Username = label,
+            DisplayName = string.IsNullOrWhiteSpace(nic) ? "AuthHex User" : nic.Trim(),
+            Status = EntityStatus.Active
+        };
+
+        try
+        {
+            _db.Users.Add(user);
+            await _db.SaveChangesAsync();
+            return user.UserId;
+        }
+        catch (DbUpdateException)
+        {
+            // Lost a race (unique auth_user_id) — the row now exists; re-read it.
+            _db.Entry(user).State = EntityState.Detached;
+            return await _db.Users.AsNoTracking()
+                .Where(u => u.AuthUserId == authUserId)
+                .Select(u => u.UserId)
+                .FirstAsync();
+        }
+    }
+}

Backend/ERPCore/Infra/Persistence/Auditing/AuditScribe.cs

@@ -0,0 +1,98 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.ChangeTracking;
+
+namespace ERPCore.Infra.Persistence.Auditing;
+
+/// <summary>A mutation captured before save, awaiting its (possibly generated) key.</summary>
+public sealed record PendingAudit(EntityEntry Entry, string EntityType, AuditAction Action, string ChangeSet, long CapturedId, bool IsAdded);
+
+/// <summary>
+/// Builds audit-trail rows from the EF change tracker (FR-X-02). High-volume /
+/// derived / self-referential tables are excluded (the stock ledger is itself the
+/// stock movement audit). Change sets are captured <b>before</b> save so old→new is
+/// accurate; generated keys for inserts are read <b>after</b> save.
+/// </summary>
+public static class AuditScribe
+{
+    private static readonly HashSet<Type> Excluded =
+    [
+        typeof(AuditLog), typeof(JournalEntryStub), typeof(NumberSequence),
+        typeof(StockLedger), typeof(StockLayer),
+    ];
+
+    private static readonly JsonSerializerOptions Json = new()
+    {
+        Converters = { new JsonStringEnumConverter() },
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+    };
+
+    public static List<PendingAudit> Capture(ChangeTracker tracker)
+    {
+        var pending = new List<PendingAudit>();
+        foreach (var entry in tracker.Entries())
+        {
+            if (entry.State is not (EntityState.Added or EntityState.Modified or EntityState.Deleted)) continue;
+            if (Excluded.Contains(entry.Entity.GetType())) continue;
+
+            var action = entry.State switch
+            {
+                EntityState.Added => AuditAction.Create,
+                EntityState.Deleted => AuditAction.Delete,
+                _ => AuditAction.Update,
+            };
+
+            var changeSet = BuildChangeSet(entry, action);
+            if (action == AuditAction.Update && changeSet == "{}") continue; // only concurrency token touched, etc.
+
+            var isAdded = entry.State == EntityState.Added;
+            pending.Add(new PendingAudit(entry, entry.Entity.GetType().Name, action, changeSet, isAdded ? 0 : ReadKey(entry), isAdded));
+        }
+        return pending;
+    }
+
+    public static AuditLog ToLog(PendingAudit p, long userId, DateTime now) => new()
+    {
+        UserId = userId,
+        EntityType = p.EntityType,
+        EntityId = p.IsAdded ? ReadKey(p.Entry) : p.CapturedId,
+        Action = p.Action,
+        ChangeSet = p.ChangeSet,
+        CreatedAt = now,
+    };
+
+    private static long ReadKey(EntityEntry entry)
+    {
+        var pk = entry.Metadata.FindPrimaryKey();
+        if (pk is null || pk.Properties.Count != 1) return 0;
+        var value = entry.Property(pk.Properties[0].Name).CurrentValue;
+        return value is null ? 0 : Convert.ToInt64(value);
+    }
+
+    private static string BuildChangeSet(EntityEntry entry, AuditAction action)
+    {
+        var set = new Dictionary<string, object?>();
+        foreach (var p in entry.Properties)
+        {
+            if (p.Metadata.IsPrimaryKey()) continue;
+            if (p.Metadata.Name == nameof(Item.RowVersion)) continue;
+
+            switch (action)
+            {
+                case AuditAction.Create when p.CurrentValue is not null:
+                    set[p.Metadata.Name] = p.CurrentValue;
+                    break;
+                case AuditAction.Delete:
+                    set[p.Metadata.Name] = p.OriginalValue;
+                    break;
+                case AuditAction.Update when p.IsModified && !Equals(p.OriginalValue, p.CurrentValue):
+                    set[p.Metadata.Name] = new Dictionary<string, object?> { ["old"] = p.OriginalValue, ["new"] = p.CurrentValue };
+                    break;
+            }
+        }
+        return JsonSerializer.Serialize(set, Json);
+    }
+}

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

@@ -0,0 +1,41 @@
+using ERPCore.Domain.Entities;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ERPCore.Infra.Persistence.Configurations;
+
+public sealed class AuditLogConfiguration : IEntityTypeConfiguration<AuditLog>
+{
+    public void Configure(EntityTypeBuilder<AuditLog> builder)
+    {
+        builder.ToTable("audit_logs");
+        builder.HasKey(a => a.AuditId);
+
+        builder.Property(a => a.EntityType).IsRequired().HasMaxLength(80);
+        builder.Property(a => a.Action).HasConversion<string>().HasMaxLength(10).IsRequired();
+        builder.Property(a => a.ChangeSet).IsRequired().HasColumnType("jsonb");
+        builder.Property(a => a.CreatedAt).IsRequired();
+
+        builder.HasOne<User>().WithMany().HasForeignKey(a => a.UserId).OnDelete(DeleteBehavior.Restrict);
+
+        builder.HasIndex(a => new { a.EntityType, a.EntityId });
+        builder.HasIndex(a => a.CreatedAt);
+        builder.HasIndex(a => a.UserId);
+    }
+}
+
+public sealed class JournalEntryStubConfiguration : IEntityTypeConfiguration<JournalEntryStub>
+{
+    public void Configure(EntityTypeBuilder<JournalEntryStub> builder)
+    {
+        builder.ToTable("journal_entry_stubs");
+        builder.HasKey(j => j.JournalId);
+
+        builder.Property(j => j.SourceDocType).IsRequired().HasMaxLength(10);
+        builder.Property(j => j.DebitAccount).IsRequired().HasMaxLength(20);
+        builder.Property(j => j.CreditAccount).IsRequired().HasMaxLength(20);
+        builder.Property(j => j.Amount).HasPrecision(18, 4);
+
+        builder.HasIndex(j => new { j.SourceDocType, j.SourceDocId });
+    }
+}

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

@@ -0,0 +1,43 @@
+using ERPCore.Domain.Entities;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ERPCore.Infra.Persistence.Configurations;
+
+public sealed class BatchConfiguration : IEntityTypeConfiguration<Batch>
+{
+    public void Configure(EntityTypeBuilder<Batch> builder)
+    {
+        builder.ToTable("batches");
+        builder.HasKey(b => b.BatchId);
+
+        builder.Property(b => b.BatchNo).IsRequired().HasMaxLength(50);
+
+        builder.HasOne(b => b.Item)
+            .WithMany()
+            .HasForeignKey(b => b.ItemId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        // Batch number unique within an item.
+        builder.HasIndex(b => new { b.ItemId, b.BatchNo }).IsUnique();
+    }
+}
+
+public sealed class SerialConfiguration : IEntityTypeConfiguration<Serial>
+{
+    public void Configure(EntityTypeBuilder<Serial> builder)
+    {
+        builder.ToTable("serials");
+        builder.HasKey(s => s.SerialId);
+
+        builder.Property(s => s.SerialNo).IsRequired().HasMaxLength(100);
+        builder.Property(s => s.Status).IsRequired().HasMaxLength(20);
+
+        builder.HasOne(s => s.Item)
+            .WithMany()
+            .HasForeignKey(s => s.ItemId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        builder.HasIndex(s => new { s.ItemId, s.SerialNo }).IsUnique();
+    }
+}

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

@@ -0,0 +1,25 @@
+using ERPCore.Domain.Entities;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ERPCore.Infra.Persistence.Configurations;
+
+public sealed class BinConfiguration : IEntityTypeConfiguration<Bin>
+{
+    public void Configure(EntityTypeBuilder<Bin> builder)
+    {
+        builder.ToTable("bins");
+        builder.HasKey(b => b.BinId);
+
+        builder.Property(b => b.Code).IsRequired().HasMaxLength(50);
+        builder.Property(b => b.BinType).HasMaxLength(50);
+
+        builder.HasOne(b => b.Warehouse)
+            .WithMany(w => w.Bins)
+            .HasForeignKey(b => b.WarehouseId)
+            .OnDelete(DeleteBehavior.Cascade);
+
+        // Bin code unique within its warehouse.
+        builder.HasIndex(b => new { b.WarehouseId, b.Code }).IsUnique();
+    }
+}