[CLAUDE] Drastic refactor: flat workflow Phòng × Cấp + Migration 21 (Chunk A)

User chốt drastic refactor — bỏ phase enum hoàn toàn, dùng ChoDuyet=10
đơn nhất + currentStepIndex tracking. Workflow flat list (Phòng × Cấp ×
Approvers). Mỗi PE/HĐ pin WorkflowDefinitionId chạy hết quy trình đó.

Schema (Migration 21 `RefactorWorkflowToFlatModel`):
- Phase enum +ChoDuyet=10 (PE + Contract). Legacy 2-9 + 98 deprecated.
- WorkflowStep + DepartmentId Guid? (FK Restrict) + PositionLevel int?
  (PE + Contract — mirror).
- PE/Contract + CurrentWorkflowStepIndex int? + RejectedAtStepIndex int?
- DROP table PurchaseEvaluationWorkflowStepInnerSteps (Mig 18)
- DROP table WorkflowStepInnerSteps (Mig 20)
- DROP column ContractDeptApproval.InnerStepId (Mig 20)
- DROP column PEDeptApproval.InnerStepId (Mig 18)
- DROP filtered indexes (Mig 19/20) + restore simple unique
  (TargetId, Phase, Dept, Stage) non-filtered

Service rewrite (PE + Contract WorkflowService.TransitionAsync):
- Phase transitions: DangSoanThao → ChoDuyet (Drafter trình, init idx=0)
- ChoDuyet → ChoDuyet (advance idx per approve)
- ChoDuyet → DaDuyet/DaPhatHanh (idx >= steps.Count → terminal)
- ChoDuyet → DangSoanThao (Trả lại — save RejectedAtStepIndex)
- ChoDuyet → TuChoi (Từ chối — khoá vĩnh viễn)
- DangSoanThao + RejectedAtStepIndex → ChoDuyet jump-back to saved idx
- Approver match: actor.Dept == step.Dept AND actor.PositionLevel >=
  step.PositionLevel (OR-of-many cùng cấp/dept = pass) OR
  Approvers.Any(Kind=User AND id match) OR
  Approvers.Any(Kind=Role AND actorRoles contains)
- Admin role bypass policy. Last step done → gen mã HĐ (Contract only)

App CQRS:
- WorkflowStepDto + WorkflowStepInput drop InnerStep, add DepartmentId
  + PositionLevel fields. PE + Contract mirror.

Tests rewrite:
- DROP PeNStageApprovalTests.cs (6 test) + ContractNStageApprovalTests.cs
  (6 test) + PeTwoStageApprovalTests.cs (7 test) — legacy N-stage/2-stage
  no longer applicable
- UPDATE PeWorkflowAdminTests signature to new flat input
- 96 → 77 test pass (drop 19 legacy)

Reference Domain entities removed:
- WorkflowStepInnerStep (Contract)
- PurchaseEvaluationWorkflowStepInnerStep (PE)
- DTOs WorkflowStepInnerStepDto / CreateWorkflowStepInnerStepInput per module

Memory `feedback_drastic_refactor_scope.md` validated: drastic refactor
done in dedicated session với context fresh, scope ~5h actual (planned ~8-10h
with 2x buffer).

Verify:
- dotnet build SolutionErp.slnx 0 error
- dotnet ef database update Mig 21 LocalDB applied OK
- dotnet test 77 pass (54 Domain + 23 Infra)
- 3-file rule: Migration .cs + Designer.cs + Snapshot updated

Pending Chunk B: FE Designer flat UI (PeWorkflowsPage + WorkflowsPage).
Pending Chunk C: FE PeWorkflowPanel + workflow timeline display.
Pending Chunk D: Docs + Skill + Memory + session log.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Backend/SolutionErp.Infrastructure/Services/ContractWorkflowService.cs

@@ -11,9 +11,10 @@ using SolutionErp.Domain.Notifications;
 
 namespace SolutionErp.Infrastructure.Services;
 
-// Thin orchestrator — all phase/role/SLA rules live in WorkflowPolicy (Domain).
-// This class is responsible only for *applying* transitions: DB writes, code
-// generation at DangDongDau, SLA deadline computation, notification dispatch.
+// Contract Workflow Service — Session 16 drastic refactor (Mig 21):
+// Flat workflow model. Mỗi step = 1 (Phòng × Cấp + Approvers). Service iterate
+// steps OrderBy Order, advance Contract.CurrentWorkflowStepIndex per approve.
+// Phase enum simplified: DangSoanThao → ChoDuyet → DaPhatHanh / TuChoi.
 public class ContractWorkflowService(
     IApplicationDbContext db,
     IContractCodeGenerator codeGenerator,
@@ -22,11 +23,8 @@ public class ContractWorkflowService(
     IChangelogService changelog,
     UserManager<User> userManager) : IContractWorkflowService
 {
-    // Expose per-policy SLA via the contract — accepts optional contract so the
-    // caller (CreateContractCommand) can ask for a specific type's SLA even
-    // before the contract exists.
     public TimeSpan? GetPhaseSla(ContractPhase phase) =>
-        WorkflowPolicies.Standard.PhaseSla.GetValueOrDefault(phase);
+        phase == ContractPhase.ChoDuyet ? TimeSpan.FromDays(7) : null;
 
     public async Task TransitionAsync(
         Contract contract,
@@ -37,378 +35,196 @@ public class ContractWorkflowService(
         string? comment,
         CancellationToken ct = default)
     {
-        if (contract.Phase == targetPhase)
-            throw new ConflictException("HĐ đã ở phase đích.");
-
-        // ===== Smart reject + resume (Phase 9 — Migration 16) =====
-        // Reject: override target = DangSoanThao + lưu phase gốc → Drafter sửa.
-        // Resume sau reject: Drafter trình từ DangSoanThao + RejectedFromPhase
-        // != null → jump straight tới phase đã reject, bypass phase trung gian.
         var fromPhase = contract.Phase;
-        var isResumingAfterReject = decision == ApprovalDecision.Approve
-            && fromPhase == ContractPhase.DangSoanThao
-            && contract.RejectedFromPhase != null;
-
-        if (decision == ApprovalDecision.Reject)
-        {
-            contract.RejectedFromPhase = fromPhase;
-            targetPhase = ContractPhase.DangSoanThao;
-
-            // N-stage state reset (Mig 20): clear inner step approval rows tại
-            // fromPhase. User resume sẽ approve lại từ inner step đầu.
-            var staleNStageRows = await db.ContractDepartmentApprovals
-                .Where(a => a.ContractId == contract.Id
-                         && a.PhaseAtApproval == (int)fromPhase
-                         && a.InnerStepId != null)
-                .ToListAsync(ct);
-            foreach (var r in staleNStageRows) db.ContractDepartmentApprovals.Remove(r);
-        }
-        else if (isResumingAfterReject)
-        {
-            targetPhase = contract.RejectedFromPhase!.Value;
-            contract.RejectedFromPhase = null;
-        }
-
-        // Resolve the workflow: prefer the pinned WorkflowDefinition (new
-        // versioned system), else fall back to the static/override registry
-        // (legacy path for contracts created before versioning rolled out).
-        WorkflowPolicy policy;
-        WorkflowDefinition? definition = null;
-        if (contract.WorkflowDefinitionId is Guid wfId)
-        {
-            definition = await db.WorkflowDefinitions.AsNoTracking()
-                .Include(d => d.Steps.OrderBy(s => s.Order))
-                    .ThenInclude(s => s.Approvers)
-                .Include(d => d.Steps)
-                    .ThenInclude(s => s.InnerSteps.OrderBy(i => i.Order))
-                .FirstOrDefaultAsync(d => d.Id == wfId, ct);
-            policy = definition is not null
-                ? WorkflowPolicyRegistry.FromDefinition(definition)
-                : WorkflowPolicyRegistry.ForContract(contract);
-        }
-        else
-        {
-            var overrides = await db.WorkflowTypeAssignments.AsNoTracking()
-                .ToDictionaryAsync(a => a.ContractType, a => a.PolicyName, ct);
-            policy = WorkflowPolicyRegistry.ForContractWithOverrides(contract, overrides);
-        }
         var isAdmin = actorRoles.Contains(AppRoles.Admin);
         var isSystem = actorUserId is null && decision == ApprovalDecision.AutoApprove;
 
-        // Policy guard — bypass cho resume (Drafter có quyền trình lại sau khi
-        // sửa, không cần policy check vì target đã pinned bởi RejectedFromPhase).
-        if (!isAdmin && !isSystem && !isResumingAfterReject)
+        // ===== REJECT BRANCH =====
+        if (decision == ApprovalDecision.Reject)
         {
-            if (!policy.Transitions.TryGetValue((fromPhase, targetPhase), out var allowedRoles))
-                throw new ForbiddenException(
-                    $"Policy '{policy.Name}' không cho phép {fromPhase} → {targetPhase}. " +
-                    $"Kiểm tra ContractType hoặc BypassProcurementAndCCM.");
-
-            // Sử dụng IsTransitionAllowed — check Role + User-kind fallback.
-            // User-kind chỉ áp dụng khi WorkflowDefinition pinned có
-            // WorkflowStepApprover Kind=User cho step này.
-            if (!policy.IsTransitionAllowed(fromPhase, targetPhase, actorRoles, actorUserId))
+            if (targetPhase == ContractPhase.TuChoi)
             {
-                var userExtra = policy.UserTransitions is not null
-                    && policy.UserTransitions.TryGetValue((fromPhase, targetPhase), out var userIds)
-                    && userIds.Length > 0
-                    ? $" hoặc {userIds.Length} user explicit"
-                    : "";
-                throw new ForbiddenException(
-                    $"Role ({string.Join(",", actorRoles)}) không đủ quyền chuyển {fromPhase} → {targetPhase}. " +
-                    $"Policy '{policy.Name}' yêu cầu: {string.Join(",", allowedRoles)}{userExtra}.");
+                contract.Phase = ContractPhase.TuChoi;
             }
+            else
+            {
+                contract.RejectedFromPhase = fromPhase;
+                contract.RejectedAtStepIndex = contract.CurrentWorkflowStepIndex;
+                contract.Phase = ContractPhase.DangSoanThao;
+                contract.CurrentWorkflowStepIndex = null;
+            }
+            contract.SlaDeadline = null;
+            await LogTransitionAsync(contract, fromPhase, contract.Phase, actorUserId, decision, comment, ct);
+            await db.SaveChangesAsync(ct);
+            return;
         }
 
-        // ===== Department approval (N-stage Mig 20 hoặc Legacy 2-stage Mig 16) =====
-        // Mirror PE workflow service. Step có InnerSteps → N-stage logic
-        // (Phòng × PositionLevel sequential). Else fallback legacy 2-stage
-        // (NV.Review/TPB.Confirm). Skip với reject + resume + admin + system.
-        var currentStepDef = definition?.Steps.FirstOrDefault(s => s.Phase == fromPhase);
-        var hasInnerSteps = currentStepDef?.InnerSteps.Count > 0;
+        // ===== RESUME AFTER REJECT =====
+        var isResumingAfterReject = decision == ApprovalDecision.Approve
+            && fromPhase == ContractPhase.DangSoanThao
+            && contract.RejectedAtStepIndex != null;
 
-        if (decision == ApprovalDecision.Approve
-            && targetPhase != ContractPhase.DangSoanThao
-            && targetPhase != ContractPhase.TuChoi
-            && !isResumingAfterReject
-            && !isAdmin && !isSystem
-            && actorUserId is Guid actorUid)
+        if (isResumingAfterReject)
         {
-            var actor = await userManager.FindByIdAsync(actorUid.ToString());
+            contract.Phase = ContractPhase.ChoDuyet;
+            contract.CurrentWorkflowStepIndex = contract.RejectedAtStepIndex;
+            contract.RejectedAtStepIndex = null;
+            contract.RejectedFromPhase = null;
+            contract.SlaDeadline = dateTime.UtcNow.AddDays(7);
+            await LogTransitionAsync(contract, fromPhase, ContractPhase.ChoDuyet, actorUserId, decision, comment, ct);
+            await db.SaveChangesAsync(ct);
+            return;
+        }
 
-            if (hasInnerSteps && currentStepDef is not null)
+        // ===== DRAFTER TRÌNH =====
+        if (fromPhase == ContractPhase.DangSoanThao
+            && (targetPhase == ContractPhase.ChoDuyet || (!isAdmin && !isSystem)))
+        {
+            if (!isAdmin && !isSystem
+                && !actorRoles.Contains(AppRoles.Drafter)
+                && !actorRoles.Contains(AppRoles.DeptManager))
             {
-                // ===== N-stage logic (Mig 20) — mirror PE Mig 18 =====
-                if (actor?.DepartmentId is null || actor.PositionLevel is null)
-                {
+                throw new ForbiddenException(
+                    $"Role ({string.Join(",", actorRoles)}) không đủ quyền trình duyệt HĐ.");
+            }
+            contract.Phase = ContractPhase.ChoDuyet;
+            contract.CurrentWorkflowStepIndex = 0;
+            contract.SlaDeadline = dateTime.UtcNow.AddDays(7);
+            await LogTransitionAsync(contract, fromPhase, ContractPhase.ChoDuyet, actorUserId, decision, comment, ct);
+            await db.SaveChangesAsync(ct);
+            return;
+        }
+
+        // ===== APPROVE STEP =====
+        if (fromPhase == ContractPhase.ChoDuyet && decision == ApprovalDecision.Approve)
+        {
+            var def = contract.WorkflowDefinitionId is Guid wfId
+                ? await db.WorkflowDefinitions.AsNoTracking()
+                    .Include(d => d.Steps.OrderBy(s => s.Order))
+                        .ThenInclude(s => s.Approvers)
+                    .FirstOrDefaultAsync(d => d.Id == wfId, ct)
+                : null;
+
+            if (def == null || def.Steps.Count == 0)
+                throw new ConflictException("HĐ chưa pin workflow definition hoặc workflow không có step.");
+
+            var steps = def.Steps.OrderBy(s => s.Order).ToList();
+            var currentIdx = contract.CurrentWorkflowStepIndex ?? 0;
+            if (currentIdx < 0 || currentIdx >= steps.Count)
+                throw new ConflictException($"CurrentWorkflowStepIndex={currentIdx} không hợp lệ.");
+
+            var currentStep = steps[currentIdx];
+
+            if (!isAdmin && !isSystem)
+            {
+                var actor = actorUserId is Guid uid ? await userManager.FindByIdAsync(uid.ToString()) : null;
+                if (actor == null)
+                    throw new ForbiddenException("Không xác định được approver.");
+
+                var matchByDeptLevel = currentStep.DepartmentId != null
+                    && currentStep.PositionLevel != null
+                    && actor.DepartmentId == currentStep.DepartmentId
+                    && actor.PositionLevel != null
+                    && (int)actor.PositionLevel >= (int)currentStep.PositionLevel;
+
+                var matchByExplicitUser = currentStep.Approvers.Any(a =>
+                    a.Kind == WorkflowApproverKind.User
+                    && Guid.TryParse(a.AssignmentValue, out var auid)
+                    && auid == actor.Id);
+
+                var matchByRole = currentStep.Approvers.Any(a =>
+                    a.Kind == WorkflowApproverKind.Role
+                    && actorRoles.Contains(a.AssignmentValue));
+
+                if (!matchByDeptLevel && !matchByExplicitUser && !matchByRole)
                     throw new ForbiddenException(
-                        "User phải có Phòng + Cấp chức danh (NV/PP/TP) để duyệt N-stage workflow.");
-                }
-
-                var actorDept = actor.DepartmentId.Value;
-                var actorPos = actor.PositionLevel.Value;
-                var canBypass = actor.CanBypassReview;
-
-                var inners = currentStepDef.InnerSteps.OrderBy(i => i.Order).ToList();
-                var innerIds = inners.Select(i => i.Id).ToList();
-
-                var existingApprovals = await db.ContractDepartmentApprovals
-                    .Where(a => a.ContractId == contract.Id
-                             && a.PhaseAtApproval == (int)fromPhase
-                             && a.InnerStepId != null
-                             && innerIds.Contains(a.InnerStepId!.Value))
-                    .ToListAsync(ct);
-                var doneInnerIds = existingApprovals.Select(a => a.InnerStepId!.Value).ToHashSet();
-
-                var pendingRequired = inners.Where(i => i.IsRequired && !doneInnerIds.Contains(i.Id)).ToList();
-                if (pendingRequired.Count > 0)
-                {
-                    var firstPending = pendingRequired[0];
-
-                    var levelOk = actorPos == firstPending.PositionLevel
-                        || (canBypass && (int)actorPos >= (int)firstPending.PositionLevel);
-                    if (actorDept != firstPending.DepartmentId || !levelOk)
-                    {
-                        throw new ForbiddenException(
-                            $"Cấp duyệt tiếp theo: phòng {firstPending.DepartmentId} cấp {firstPending.PositionLevel}. " +
-                            $"Bạn (phòng {actorDept} cấp {actorPos}{(canBypass ? "+bypass" : "")}) không khớp.");
-                    }
-
-                    var rowsToCreate = new List<(WorkflowStepInnerStep i, bool bypassed)>();
-                    if (actorPos == firstPending.PositionLevel)
-                    {
-                        rowsToCreate.Add((firstPending, false));
-                    }
-                    else
-                    {
-                        // Bypass cùng dept: upsert tất cả pending inner trong dept actor
-                        // có level từ firstPending.PositionLevel đến actorPos (inclusive)
-                        foreach (var inner in inners
-                            .Where(i => i.DepartmentId == actorDept
-                                     && (int)i.PositionLevel >= (int)firstPending.PositionLevel
-                                     && (int)i.PositionLevel <= (int)actorPos
-                                     && !doneInnerIds.Contains(i.Id)))
-                        {
-                            rowsToCreate.Add((inner, inner.PositionLevel != actorPos));
-                        }
-                    }
-
-                    var nowUtc = dateTime.UtcNow;
-                    foreach (var (inner, bypassed) in rowsToCreate)
-                    {
-                        db.ContractDepartmentApprovals.Add(new ContractDepartmentApproval
-                        {
-                            ContractId = contract.Id,
-                            PhaseAtApproval = (int)fromPhase,
-                            DepartmentId = inner.DepartmentId,
-                            Stage = ApprovalStage.Confirm,
-                            ApproverUserId = actorUid,
-                            ApproverRoleSnapshot = $"{inner.PositionLevel}{(bypassed ? "(bypass)" : "")}",
-                            Comment = comment,
-                            ApprovedAt = nowUtc,
-                            IsBypassed = bypassed,
-                            InnerStepId = inner.Id,
-                        });
-                        doneInnerIds.Add(inner.Id);
-                    }
-
-                    var stillPending = inners.Any(i => i.IsRequired && !doneInnerIds.Contains(i.Id));
-                    if (stillPending)
-                    {
-                        db.ContractApprovals.Add(new ContractApproval
-                        {
-                            ContractId = contract.Id,
-                            FromPhase = fromPhase,
-                            ToPhase = fromPhase,
-                            ApproverUserId = actorUid,
-                            Decision = ApprovalDecision.Approve,
-                            Comment = $"[Inner step duyệt {actorPos}] {comment ?? ""}",
-                            ApprovedAt = nowUtc,
-                        });
-
-                        string? reviewerName = actor.FullName ?? actor.Email;
-                        db.ContractChangelogs.Add(new ContractChangelog
-                        {
-                            ContractId = contract.Id,
-                            EntityType = ChangelogEntityType.Workflow,
-                            Action = ChangelogAction.Transition,
-                            PhaseAtChange = fromPhase,
-                            UserId = actorUid,
-                            UserName = reviewerName ?? "Hệ thống",
-                            Summary = $"{reviewerName} duyệt cấp {actorPos} phase {fromPhase} (còn {inners.Count(i => i.IsRequired && !doneInnerIds.Contains(i.Id))} cấp pending)",
-                            ContextNote = comment,
-                        });
-
-                        await db.SaveChangesAsync(ct);
-                        return;
-                    }
-                    // All required inner steps done → fall through phase transition
-                }
+                        $"Step {currentIdx + 1} ({currentStep.Name}) yêu cầu phòng={currentStep.DepartmentId}, cấp={currentStep.PositionLevel}. Bạn không khớp.");
             }
-            else if (actor?.DepartmentId is Guid deptId)
+
+            db.ContractApprovals.Add(new ContractApproval
             {
-                // ===== Legacy 2-stage logic (Mig 16) — fallback khi step KHÔNG có InnerSteps =====
-                var isManager = actorRoles.Contains(AppRoles.DeptManager);
-                var canBypass = actor.CanBypassReview;
-                var stage = (isManager || canBypass) ? ApprovalStage.Confirm : ApprovalStage.Review;
-                var isBypassed = !isManager && canBypass;
-                var roleSnapshot = isManager ? "TPB" : (canBypass ? "NV(bypass)" : "NV");
+                ContractId = contract.Id,
+                FromPhase = fromPhase,
+                ToPhase = fromPhase,
+                ApproverUserId = actorUserId,
+                Decision = decision,
+                Comment = $"[Step {currentIdx + 1}] {comment ?? ""}",
+                ApprovedAt = dateTime.UtcNow,
+            });
 
-                var existing = await db.ContractDepartmentApprovals
-                    .FirstOrDefaultAsync(a =>
-                        a.ContractId == contract.Id
-                        && a.PhaseAtApproval == (int)fromPhase
-                        && a.DepartmentId == deptId
-                        && a.Stage == stage
-                        && a.InnerStepId == null, ct);
-                if (existing is null)
+            var nextIdx = currentIdx + 1;
+            if (nextIdx >= steps.Count)
+            {
+                // All steps done — gen mã HĐ + DaPhatHanh
+                if (string.IsNullOrEmpty(contract.MaHopDong))
                 {
-                    db.ContractDepartmentApprovals.Add(new ContractDepartmentApproval
-                    {
-                        ContractId = contract.Id,
-                        PhaseAtApproval = (int)fromPhase,
-                        DepartmentId = deptId,
-                        Stage = stage,
-                        ApproverUserId = actorUid,
-                        ApproverRoleSnapshot = roleSnapshot,
-                        Comment = comment,
-                        ApprovedAt = dateTime.UtcNow,
-                        IsBypassed = isBypassed,
-                        InnerStepId = null,
-                    });
-                }
-                else
-                {
-                    existing.ApproverUserId = actorUid;
-                    existing.ApproverRoleSnapshot = roleSnapshot;
-                    existing.Comment = comment;
-                    existing.ApprovedAt = dateTime.UtcNow;
-                    existing.IsBypassed = isBypassed;
-                }
-
-                var hasConfirm = stage == ApprovalStage.Confirm
-                    || await db.ContractDepartmentApprovals.AnyAsync(a =>
-                        a.ContractId == contract.Id
-                        && a.PhaseAtApproval == (int)fromPhase
-                        && a.DepartmentId == deptId
-                        && a.Stage == ApprovalStage.Confirm
-                        && a.InnerStepId == null, ct);
-
-                if (!hasConfirm)
-                {
-                    db.ContractApprovals.Add(new ContractApproval
-                    {
-                        ContractId = contract.Id,
-                        FromPhase = fromPhase,
-                        ToPhase = fromPhase,
-                        ApproverUserId = actorUid,
-                        Decision = ApprovalDecision.Approve,
-                        Comment = $"[Review NV] {comment ?? ""}",
-                        ApprovedAt = dateTime.UtcNow,
-                    });
-
-                    string? reviewerName = actor.FullName ?? actor.Email;
-                    db.ContractChangelogs.Add(new ContractChangelog
-                    {
-                        ContractId = contract.Id,
-                        EntityType = ChangelogEntityType.Workflow,
-                        Action = ChangelogAction.Transition,
-                        PhaseAtChange = fromPhase,
-                        UserId = actorUid,
-                        UserName = reviewerName ?? "Hệ thống",
-                        Summary = $"{reviewerName} (NV) đã review phase {fromPhase}, chờ TPB confirm",
-                        ContextNote = comment,
-                    });
-
-                    // Notify TPB cùng dept để confirm. Best effort.
-                    try
-                    {
-                        var managers = await db.Users.AsNoTracking()
-                            .Where(u => u.DepartmentId == deptId && u.Id != actorUid && u.IsActive)
-                            .Select(u => u.Id)
-                            .ToListAsync(ct);
-                        foreach (var mgrId in managers)
-                        {
-                            var mgr = await userManager.FindByIdAsync(mgrId.ToString());
-                            if (mgr is null) continue;
-                            var roles = await userManager.GetRolesAsync(mgr);
-                            if (!roles.Contains(AppRoles.DeptManager)) continue;
-
-                            await notifications.NotifyAsync(
-                                mgrId,
-                                NotificationType.ContractPhaseTransition,
-                                title: $"HĐ {contract.MaHopDong ?? contract.TenHopDong ?? ""} chờ TPB confirm",
-                                description: $"NV {reviewerName} đã review phase {fromPhase}. Vui lòng vào confirm để workflow tiếp tục.",
-                                href: $"/contracts/{contract.Id}",
-                                refId: contract.Id,
-                                ct: ct);
-                        }
-                    }
-                    catch { /* notification fail non-critical */ }
-
-                    await db.SaveChangesAsync(ct);
-                    return;
+                    var supplier = await db.Suppliers.FirstOrDefaultAsync(s => s.Id == contract.SupplierId, ct)
+                        ?? throw new NotFoundException("Supplier", contract.SupplierId);
+                    var project = await db.Projects.FirstOrDefaultAsync(p => p.Id == contract.ProjectId, ct)
+                        ?? throw new NotFoundException("Project", contract.ProjectId);
+                    contract.MaHopDong = await codeGenerator.GenerateAsync(contract, project.Code, supplier.Code, ct);
                 }
+                contract.Phase = ContractPhase.DaPhatHanh;
+                contract.CurrentWorkflowStepIndex = null;
+                contract.SlaDeadline = null;
+                await LogTransitionAsync(contract, fromPhase, ContractPhase.DaPhatHanh, actorUserId, decision, comment, ct);
             }
+            else
+            {
+                contract.CurrentWorkflowStepIndex = nextIdx;
+                contract.SlaDeadline = dateTime.UtcNow.AddDays(7);
+                await LogTransitionAsync(contract, fromPhase, fromPhase, actorUserId, decision,
+                    $"Hoàn tất step {currentIdx + 1}/{steps.Count}, sang step {nextIdx + 1}", ct);
+            }
+            await db.SaveChangesAsync(ct);
+            return;
         }
 
-        // Defensive — gen mã HĐ nếu chưa có khi chuyển sang DangDongDau.
-        // Nominal flow (sau user feedback): mã đã gen sẵn từ CreateContract → skip.
-        // Fallback chỉ trigger cho HĐ legacy chưa qua backfill, hoặc HĐ tạo bằng
-        // path khác (vd seed/import) chưa set MaHopDong.
-        if (targetPhase == ContractPhase.DangDongDau && string.IsNullOrEmpty(contract.MaHopDong))
+        // Admin manual override
+        if (isAdmin)
         {
-            var supplier = await db.Suppliers.FirstOrDefaultAsync(s => s.Id == contract.SupplierId, ct)
-                ?? throw new NotFoundException("Supplier", contract.SupplierId);
-            var project = await db.Projects.FirstOrDefaultAsync(p => p.Id == contract.ProjectId, ct)
-                ?? throw new NotFoundException("Project", contract.ProjectId);
-            contract.MaHopDong = await codeGenerator.GenerateAsync(contract, project.Code, supplier.Code, ct);
+            contract.Phase = targetPhase;
+            contract.SlaDeadline = targetPhase == ContractPhase.ChoDuyet
+                ? dateTime.UtcNow.AddDays(7) : null;
+            await LogTransitionAsync(contract, fromPhase, targetPhase, actorUserId, decision, comment, ct);
+            await db.SaveChangesAsync(ct);
+            return;
         }
 
-        contract.SlaWarningSent = false;
-        contract.Phase = targetPhase;
+        throw new ConflictException($"Transition {fromPhase} → {targetPhase} không hỗ trợ.");
+    }
 
-        var sla = policy.PhaseSla.GetValueOrDefault(targetPhase);
-        contract.SlaDeadline = sla is null ? null : dateTime.UtcNow.Add(sla.Value);
-
-        db.ContractApprovals.Add(new ContractApproval
-        {
-            ContractId = contract.Id,
-            FromPhase = fromPhase,
-            ToPhase = targetPhase,
-            ApproverUserId = actorUserId,
-            Decision = decision,
-            Comment = comment,
-            ApprovedAt = dateTime.UtcNow,
-        });
-
-        // Log workflow transition vào unified Changelog (cho user xem trên tab Lịch sử)
-        await changelog.LogWorkflowTransitionAsync(contract.Id, fromPhase, targetPhase, comment);
+    private async Task LogTransitionAsync(
+        Contract contract,
+        ContractPhase fromPhase,
+        ContractPhase toPhase,
+        Guid? actorUserId,
+        ApprovalDecision decision,
+        string? comment,
+        CancellationToken ct)
+    {
+        await changelog.LogWorkflowTransitionAsync(contract.Id, fromPhase, toPhase, comment);
 
         if (contract.DrafterUserId is Guid drafterId && drafterId != actorUserId)
         {
-            var title = targetPhase switch
+            var (title, type) = toPhase switch
             {
-                ContractPhase.DaPhatHanh => $"HĐ {contract.MaHopDong ?? contract.TenHopDong} đã phát hành",
-                ContractPhase.TuChoi => $"HĐ {contract.TenHopDong ?? "của bạn"} bị từ chối",
-                _ => $"HĐ {contract.TenHopDong ?? contract.MaHopDong ?? ""} chuyển sang phase mới",
-            };
-            var type = targetPhase switch
-            {
-                ContractPhase.DaPhatHanh => NotificationType.ContractPublished,
-                ContractPhase.TuChoi => NotificationType.ContractRejected,
-                _ => NotificationType.ContractPhaseTransition,
+                ContractPhase.DaPhatHanh => ($"HĐ {contract.MaHopDong ?? contract.TenHopDong} đã phát hành",
+                                              NotificationType.ContractPublished),
+                ContractPhase.TuChoi => ($"HĐ {contract.TenHopDong ?? "của bạn"} bị từ chối",
+                                          NotificationType.ContractRejected),
+                ContractPhase.DangSoanThao when fromPhase == ContractPhase.ChoDuyet =>
+                    ($"HĐ {contract.TenHopDong ?? "của bạn"} bị trả lại — vui lòng sửa và trình lại",
+                     NotificationType.ContractRejected),
+                _ => ($"HĐ {contract.TenHopDong ?? contract.MaHopDong ?? ""} chuyển phase mới",
+                      NotificationType.ContractPhaseTransition),
             };
             await notifications.NotifyAsync(
-                drafterId,
-                type,
-                title,
-                description: $"{fromPhase} → {targetPhase}" + (string.IsNullOrWhiteSpace(comment) ? "" : $" · {comment}"),
+                drafterId, type, title,
+                description: $"{fromPhase} → {toPhase}" + (string.IsNullOrWhiteSpace(comment) ? "" : $" · {comment}"),
                 href: $"/contracts/{contract.Id}",
                 refId: contract.Id,
                 ct: ct);
         }
-
-        await db.SaveChangesAsync(ct);
     }
 }

src/Backend/SolutionErp.Infrastructure/Services/PurchaseEvaluationWorkflowService.cs

@@ -12,8 +12,11 @@ using SolutionErp.Domain.PurchaseEvaluations;
 
 namespace SolutionErp.Infrastructure.Services;
 
-// Mirror ContractWorkflowService. Load policy từ pinned
-// WorkflowDefinition (nếu có) hoặc fallback hardcoded registry.
+// PE Workflow Service — Session 16 drastic refactor (Mig 21):
+// Flat workflow model. Mỗi step = 1 (Phòng × Cấp + Approvers). Service iterate
+// steps OrderBy Order, advance PE.CurrentWorkflowStepIndex per approve.
+// Phase enum simplified: DangSoanThao → ChoDuyet (active workflow) → DaDuyet
+// (terminal) / TuChoi (khoá). Trả lại = về DangSoanThao + save RejectedAtStepIndex.
 public class PurchaseEvaluationWorkflowService(
     IApplicationDbContext db,
     IDateTime dateTime,
@@ -21,7 +24,7 @@ public class PurchaseEvaluationWorkflowService(
     UserManager<User> userManager) : IPurchaseEvaluationWorkflowService
 {
     public TimeSpan? GetPhaseSla(PurchaseEvaluationPhase phase) =>
-        PurchaseEvaluationPolicies.NccOnly.PhaseSla.GetValueOrDefault(phase);
+        phase == PurchaseEvaluationPhase.ChoDuyet ? TimeSpan.FromDays(7) : null;
 
     public async Task TransitionAsync(
         PurchaseEvaluation evaluation,
@@ -32,345 +35,173 @@ public class PurchaseEvaluationWorkflowService(
         string? comment,
         CancellationToken ct = default)
     {
-        if (evaluation.Phase == targetPhase)
-            throw new ConflictException("Phiếu đã ở phase đích.");
-
-        // ===== Smart reject + resume (Phase 9 — Migration 16) =====
         var fromPhase = evaluation.Phase;
-        var isResumingAfterReject = decision == ApprovalDecision.Approve
-            && fromPhase == PurchaseEvaluationPhase.DangSoanThao
-            && evaluation.RejectedFromPhase != null;
-
-        if (decision == ApprovalDecision.Reject)
-        {
-            // 2 loại Reject (Session 14):
-            //  - target=TuChoi: "Từ chối hoàn toàn" — phiếu khoá vĩnh viễn (Phase=TuChoi
-            //    → 17 handler Mig 16 lock edit). Drafter phải tạo phiếu mới. KHÔNG set
-            //    RejectedFromPhase + KHÔNG clear N-stage (không resume).
-            //  - target khác (thường = DangSoanThao): "Trả lại" — smart reject pattern
-            //    Mig 16. Set RejectedFromPhase + force DangSoanThao + clear N-stage rows
-            //    tại fromPhase → Drafter sửa rồi trình lại jump-back tới phase đã reject.
-            if (targetPhase != PurchaseEvaluationPhase.TuChoi)
-            {
-                evaluation.RejectedFromPhase = fromPhase;
-                targetPhase = PurchaseEvaluationPhase.DangSoanThao;
-
-                var staleNStageRows = await db.PurchaseEvaluationDepartmentApprovals
-                    .Where(a => a.PurchaseEvaluationId == evaluation.Id
-                             && a.PhaseAtApproval == (int)fromPhase
-                             && a.InnerStepId != null)
-                    .ToListAsync(ct);
-                foreach (var r in staleNStageRows) db.PurchaseEvaluationDepartmentApprovals.Remove(r);
-            }
-        }
-        else if (isResumingAfterReject)
-        {
-            targetPhase = evaluation.RejectedFromPhase!.Value;
-            evaluation.RejectedFromPhase = null;
-        }
-
-        PurchaseEvaluationPolicy policy;
-        PurchaseEvaluationWorkflowDefinition? definition = null;
-        if (evaluation.WorkflowDefinitionId is Guid wfId)
-        {
-            definition = await db.PurchaseEvaluationWorkflowDefinitions.AsNoTracking()
-                .Include(d => d.Steps.OrderBy(s => s.Order))
-                    .ThenInclude(s => s.Approvers)
-                .Include(d => d.Steps)
-                    .ThenInclude(s => s.InnerSteps.OrderBy(i => i.Order))
-                .FirstOrDefaultAsync(d => d.Id == wfId, ct);
-            policy = definition is not null
-                ? PurchaseEvaluationPolicyRegistry.FromDefinition(definition)
-                : PurchaseEvaluationPolicyRegistry.ForEvaluation(evaluation);
-        }
-        else
-        {
-            policy = PurchaseEvaluationPolicyRegistry.ForEvaluation(evaluation);
-        }
-
         var isAdmin = actorRoles.Contains(AppRoles.Admin);
         var isSystem = actorUserId is null && decision == ApprovalDecision.AutoApprove;
 
-        // Policy guard — bypass khi resume sau reject (target đã pinned).
-        if (!isAdmin && !isSystem && !isResumingAfterReject)
+        // ===== REJECT BRANCH =====
+        if (decision == ApprovalDecision.Reject)
         {
-            if (!policy.Transitions.TryGetValue((fromPhase, targetPhase), out var allowedRoles))
-                throw new ForbiddenException(
-                    $"Policy '{policy.Name}' không cho phép {fromPhase} → {targetPhase}.");
-
-            if (!policy.IsTransitionAllowed(fromPhase, targetPhase, actorRoles, actorUserId))
+            if (targetPhase == PurchaseEvaluationPhase.TuChoi)
             {
-                throw new ForbiddenException(
-                    $"Role ({string.Join(",", actorRoles)}) không đủ quyền chuyển {fromPhase} → {targetPhase}. " +
-                    $"Policy '{policy.Name}' yêu cầu: {string.Join(",", allowedRoles)}.");
+                // Từ chối hoàn toàn — phiếu khoá vĩnh viễn (lock edit Mig 16).
+                evaluation.Phase = PurchaseEvaluationPhase.TuChoi;
             }
+            else
+            {
+                // Trả lại — về DangSoanThao + save RejectedAtStepIndex (resume jump-back).
+                evaluation.RejectedFromPhase = fromPhase;
+                evaluation.RejectedAtStepIndex = evaluation.CurrentWorkflowStepIndex;
+                evaluation.Phase = PurchaseEvaluationPhase.DangSoanThao;
+                evaluation.CurrentWorkflowStepIndex = null;
+            }
+            evaluation.SlaDeadline = null;
+            await LogTransitionAsync(evaluation, fromPhase, evaluation.Phase, actorUserId, decision, comment, ct);
+            await db.SaveChangesAsync(ct);
+            return;
         }
 
-        // ===== Department approval (N-stage Mig 18 hoặc Legacy 2-stage Mig 16) =====
-        // Active block khi: Approve + chuyển sang phase trung gian (không phải
-        // DangSoanThao/TuChoi) + KHÔNG admin/system + KHÔNG resume sau reject.
-        var currentStepDef = definition?.Steps.FirstOrDefault(s => s.Phase == fromPhase);
-        var hasInnerSteps = currentStepDef?.InnerSteps.Count > 0;
+        // ===== RESUME AFTER REJECT (Drafter trình lại) =====
+        var isResumingAfterReject = decision == ApprovalDecision.Approve
+            && fromPhase == PurchaseEvaluationPhase.DangSoanThao
+            && evaluation.RejectedAtStepIndex != null;
 
-        if (decision == ApprovalDecision.Approve
-            && targetPhase != PurchaseEvaluationPhase.DangSoanThao
-            && targetPhase != PurchaseEvaluationPhase.TuChoi
-            && !isResumingAfterReject
-            && !isAdmin && !isSystem
-            && actorUserId is Guid actorUid)
+        if (isResumingAfterReject)
         {
-            var actor = await userManager.FindByIdAsync(actorUid.ToString());
+            evaluation.Phase = PurchaseEvaluationPhase.ChoDuyet;
+            evaluation.CurrentWorkflowStepIndex = evaluation.RejectedAtStepIndex;
+            evaluation.RejectedAtStepIndex = null;
+            evaluation.RejectedFromPhase = null;
+            evaluation.SlaDeadline = dateTime.UtcNow.AddDays(7);
+            await LogTransitionAsync(evaluation, fromPhase, PurchaseEvaluationPhase.ChoDuyet, actorUserId, decision, comment, ct);
+            await db.SaveChangesAsync(ct);
+            return;
+        }
 
-            if (hasInnerSteps && currentStepDef is not null)
+        // ===== DRAFTER TRÌNH (DangSoanThao → ChoDuyet) =====
+        if (fromPhase == PurchaseEvaluationPhase.DangSoanThao
+            && (targetPhase == PurchaseEvaluationPhase.ChoDuyet || !isAdmin && !isSystem))
+        {
+            // Drafter/DeptManager only (or Admin bypass).
+            if (!isAdmin && !isSystem
+                && !actorRoles.Contains(AppRoles.Drafter)
+                && !actorRoles.Contains(AppRoles.DeptManager))
             {
-                // ===== N-stage logic (Mig 18) =====
-                // Yêu cầu user có DepartmentId + PositionLevel set. Match exact
-                // (DeptId + PositionLevel) inner step pending tiếp theo theo Order.
-                // Bypass: actor cùng dept + PositionLevel cao hơn + CanBypassReview
-                //         → batch upsert luôn các inner step cấp dưới (audit IsBypassed=true).
-                if (actor?.DepartmentId is null || actor.PositionLevel is null)
-                {
+                throw new ForbiddenException(
+                    $"Role ({string.Join(",", actorRoles)}) không đủ quyền trình duyệt phiếu.");
+            }
+            evaluation.Phase = PurchaseEvaluationPhase.ChoDuyet;
+            evaluation.CurrentWorkflowStepIndex = 0;
+            evaluation.SlaDeadline = dateTime.UtcNow.AddDays(7);
+            await LogTransitionAsync(evaluation, fromPhase, PurchaseEvaluationPhase.ChoDuyet, actorUserId, decision, comment, ct);
+            await db.SaveChangesAsync(ct);
+            return;
+        }
+
+        // ===== APPROVE STEP (advance pointer trong ChoDuyet) =====
+        if (fromPhase == PurchaseEvaluationPhase.ChoDuyet && decision == ApprovalDecision.Approve)
+        {
+            var def = evaluation.WorkflowDefinitionId is Guid wfId
+                ? await db.PurchaseEvaluationWorkflowDefinitions.AsNoTracking()
+                    .Include(d => d.Steps.OrderBy(s => s.Order))
+                        .ThenInclude(s => s.Approvers)
+                    .FirstOrDefaultAsync(d => d.Id == wfId, ct)
+                : null;
+
+            if (def == null || def.Steps.Count == 0)
+                throw new ConflictException("Phiếu chưa pin workflow definition hoặc workflow không có step.");
+
+            var steps = def.Steps.OrderBy(s => s.Order).ToList();
+            var currentIdx = evaluation.CurrentWorkflowStepIndex ?? 0;
+            if (currentIdx < 0 || currentIdx >= steps.Count)
+                throw new ConflictException($"CurrentWorkflowStepIndex={currentIdx} không hợp lệ (max={steps.Count - 1}).");
+
+            var currentStep = steps[currentIdx];
+
+            // Match approver — admin bypass policy
+            if (!isAdmin && !isSystem)
+            {
+                var actor = actorUserId is Guid uid ? await userManager.FindByIdAsync(uid.ToString()) : null;
+                if (actor == null)
+                    throw new ForbiddenException("Không xác định được approver.");
+
+                var matchByDeptLevel = currentStep.DepartmentId != null
+                    && currentStep.PositionLevel != null
+                    && actor.DepartmentId == currentStep.DepartmentId
+                    && actor.PositionLevel != null
+                    && (int)actor.PositionLevel >= (int)currentStep.PositionLevel;
+
+                var matchByExplicitUser = currentStep.Approvers.Any(a =>
+                    a.Kind == WorkflowApproverKind.User
+                    && Guid.TryParse(a.AssignmentValue, out var auid)
+                    && auid == actor.Id);
+
+                var matchByRole = currentStep.Approvers.Any(a =>
+                    a.Kind == WorkflowApproverKind.Role
+                    && actorRoles.Contains(a.AssignmentValue));
+
+                if (!matchByDeptLevel && !matchByExplicitUser && !matchByRole)
                     throw new ForbiddenException(
-                        "User phải có Phòng + Cấp chức danh (NV/PP/TP) để duyệt N-stage workflow.");
-                }
-
-                var actorDept = actor.DepartmentId.Value;
-                var actorPos = actor.PositionLevel.Value;
-                var canBypass = actor.CanBypassReview;
-
-                var inners = currentStepDef.InnerSteps.OrderBy(i => i.Order).ToList();
-                var innerIds = inners.Select(i => i.Id).ToList();
-
-                var existingApprovals = await db.PurchaseEvaluationDepartmentApprovals
-                    .Where(a => a.PurchaseEvaluationId == evaluation.Id
-                             && a.PhaseAtApproval == (int)fromPhase
-                             && a.InnerStepId != null
-                             && innerIds.Contains(a.InnerStepId!.Value))
-                    .ToListAsync(ct);
-                var doneInnerIds = existingApprovals.Select(a => a.InnerStepId!.Value).ToHashSet();
-
-                var pendingRequired = inners.Where(i => i.IsRequired && !doneInnerIds.Contains(i.Id)).ToList();
-                if (pendingRequired.Count > 0)
-                {
-                    var firstPending = pendingRequired[0];
-
-                    // Match: same dept AND (exact level OR canBypass + level higher)
-                    var levelOk = actorPos == firstPending.PositionLevel
-                        || (canBypass && (int)actorPos >= (int)firstPending.PositionLevel);
-                    if (actorDept != firstPending.DepartmentId || !levelOk)
-                    {
-                        throw new ForbiddenException(
-                            $"Cấp duyệt tiếp theo: phòng {firstPending.DepartmentId} cấp {firstPending.PositionLevel}. " +
-                            $"Bạn (phòng {actorDept} cấp {actorPos}{(canBypass ? "+bypass" : "")}) không khớp.");
-                    }
-
-                    // Determine rows to upsert
-                    var rowsToCreate = new List<(PurchaseEvaluationWorkflowStepInnerStep i, bool bypassed)>();
-                    if (actorPos == firstPending.PositionLevel)
-                    {
-                        rowsToCreate.Add((firstPending, false));
-                    }
-                    else
-                    {
-                        // Bypass cùng dept: upsert tất cả pending inner trong dept actor có level
-                        // từ firstPending.PositionLevel đến actorPos (inclusive)
-                        foreach (var inner in inners
-                            .Where(i => i.DepartmentId == actorDept
-                                     && (int)i.PositionLevel >= (int)firstPending.PositionLevel
-                                     && (int)i.PositionLevel <= (int)actorPos
-                                     && !doneInnerIds.Contains(i.Id)))
-                        {
-                            rowsToCreate.Add((inner, inner.PositionLevel != actorPos));
-                        }
-                    }
-
-                    var nowUtc = dateTime.UtcNow;
-                    foreach (var (inner, bypassed) in rowsToCreate)
-                    {
-                        db.PurchaseEvaluationDepartmentApprovals.Add(new PurchaseEvaluationDepartmentApproval
-                        {
-                            PurchaseEvaluationId = evaluation.Id,
-                            PhaseAtApproval = (int)fromPhase,
-                            DepartmentId = inner.DepartmentId,
-                            Stage = ApprovalStage.Confirm,    // N-stage: tất cả row dùng Confirm semantically
-                            ApproverUserId = actorUid,
-                            ApproverRoleSnapshot = $"{inner.PositionLevel}{(bypassed ? "(bypass)" : "")}",
-                            Comment = comment,
-                            ApprovedAt = nowUtc,
-                            IsBypassed = bypassed,
-                            InnerStepId = inner.Id,
-                        });
-                        doneInnerIds.Add(inner.Id);
-                    }
-
-                    // Recheck remaining pending sau upsert
-                    var stillPending = inners.Any(i => i.IsRequired && !doneInnerIds.Contains(i.Id));
-                    if (stillPending)
-                    {
-                        // Còn cấp duyệt tiếp theo → BLOCK phase transition.
-                        // Log Approval (review-style) + Changelog audit.
-                        db.PurchaseEvaluationApprovals.Add(new PurchaseEvaluationApproval
-                        {
-                            PurchaseEvaluationId = evaluation.Id,
-                            FromPhase = fromPhase,
-                            ToPhase = fromPhase,
-                            ApproverUserId = actorUid,
-                            Decision = ApprovalDecision.Approve,
-                            Comment = $"[Inner step duyệt {actorPos}] {comment ?? ""}",
-                            ApprovedAt = nowUtc,
-                        });
-
-                        string? reviewerName = actor.FullName ?? actor.Email;
-                        db.PurchaseEvaluationChangelogs.Add(new PurchaseEvaluationChangelog
-                        {
-                            PurchaseEvaluationId = evaluation.Id,
-                            EntityType = PurchaseEvaluationEntityType.Workflow,
-                            Action = ChangelogAction.Transition,
-                            PhaseAtChange = fromPhase,
-                            UserId = actorUid,
-                            UserName = reviewerName ?? "Hệ thống",
-                            Summary = $"{reviewerName} duyệt cấp {actorPos} phase {fromPhase} (còn {inners.Count(i => i.IsRequired && !doneInnerIds.Contains(i.Id))} cấp pending)",
-                            ContextNote = comment,
-                        });
-
-                        await db.SaveChangesAsync(ct);
-                        return;
-                    }
-                    // All required inner steps done → fall through to phase transition
-                }
-                // pendingRequired.Count == 0 → all already done before this call → fall through
+                        $"Step {currentIdx + 1} ({currentStep.Name}) yêu cầu phòng={currentStep.DepartmentId}, cấp={currentStep.PositionLevel}. Bạn không khớp.");
             }
-            else if (actor?.DepartmentId is Guid deptId)
+
+            // Log approval row
+            db.PurchaseEvaluationApprovals.Add(new PurchaseEvaluationApproval
             {
-                // ===== Legacy 2-stage logic (Mig 16) — fallback khi step KHÔNG có InnerSteps =====
-                var isManager = actorRoles.Contains(AppRoles.DeptManager);
-                var canBypass = actor.CanBypassReview;
-                var stage = (isManager || canBypass) ? ApprovalStage.Confirm : ApprovalStage.Review;
-                var isBypassed = !isManager && canBypass;
-                var roleSnapshot = isManager ? "TPB" : (canBypass ? "NV(bypass)" : "NV");
+                PurchaseEvaluationId = evaluation.Id,
+                FromPhase = fromPhase,
+                ToPhase = fromPhase,    // step advance — phase same
+                ApproverUserId = actorUserId,
+                Decision = decision,
+                Comment = $"[Step {currentIdx + 1}] {comment ?? ""}",
+                ApprovedAt = dateTime.UtcNow,
+            });
 
-                // Upsert: 1 row mỗi (PEId, phase, dept, stage). UNIQUE filtered InnerStepId IS NULL.
-                var existing = await db.PurchaseEvaluationDepartmentApprovals
-                    .FirstOrDefaultAsync(a =>
-                        a.PurchaseEvaluationId == evaluation.Id
-                        && a.PhaseAtApproval == (int)fromPhase
-                        && a.DepartmentId == deptId
-                        && a.Stage == stage
-                        && a.InnerStepId == null, ct);
-                if (existing is null)
-                {
-                    db.PurchaseEvaluationDepartmentApprovals.Add(new PurchaseEvaluationDepartmentApproval
-                    {
-                        PurchaseEvaluationId = evaluation.Id,
-                        PhaseAtApproval = (int)fromPhase,
-                        DepartmentId = deptId,
-                        Stage = stage,
-                        ApproverUserId = actorUid,
-                        ApproverRoleSnapshot = roleSnapshot,
-                        Comment = comment,
-                        ApprovedAt = dateTime.UtcNow,
-                        IsBypassed = isBypassed,
-                        InnerStepId = null,
-                    });
-                }
-                else
-                {
-                    existing.ApproverUserId = actorUid;
-                    existing.ApproverRoleSnapshot = roleSnapshot;
-                    existing.Comment = comment;
-                    existing.ApprovedAt = dateTime.UtcNow;
-                    existing.IsBypassed = isBypassed;
-                }
-
-                // Check Stage=Confirm tồn tại cho (PEId, fromPhase, deptId)
-                var hasConfirm = stage == ApprovalStage.Confirm
-                    || await db.PurchaseEvaluationDepartmentApprovals.AnyAsync(a =>
-                        a.PurchaseEvaluationId == evaluation.Id
-                        && a.PhaseAtApproval == (int)fromPhase
-                        && a.DepartmentId == deptId
-                        && a.Stage == ApprovalStage.Confirm
-                        && a.InnerStepId == null, ct);
-
-                if (!hasConfirm)
-                {
-                    // NV review xong, chưa có TPB confirm → BLOCK phase transition.
-                    db.PurchaseEvaluationApprovals.Add(new PurchaseEvaluationApproval
-                    {
-                        PurchaseEvaluationId = evaluation.Id,
-                        FromPhase = fromPhase,
-                        ToPhase = fromPhase,
-                        ApproverUserId = actorUid,
-                        Decision = ApprovalDecision.Approve,
-                        Comment = $"[Review NV] {comment ?? ""}",
-                        ApprovedAt = dateTime.UtcNow,
-                    });
-
-                    string? reviewerName = actor.FullName ?? actor.Email;
-                    db.PurchaseEvaluationChangelogs.Add(new PurchaseEvaluationChangelog
-                    {
-                        PurchaseEvaluationId = evaluation.Id,
-                        EntityType = PurchaseEvaluationEntityType.Workflow,
-                        Action = ChangelogAction.Transition,
-                        PhaseAtChange = fromPhase,
-                        UserId = actorUid,
-                        UserName = reviewerName ?? "Hệ thống",
-                        Summary = $"{reviewerName} (NV) đã review phase {fromPhase}, chờ TPB confirm",
-                        ContextNote = comment,
-                    });
-
-                    // Notify TPB cùng dept để confirm. Best effort — fail OK.
-                    try
-                    {
-                        var managers = await db.Users.AsNoTracking()
-                            .Where(u => u.DepartmentId == deptId && u.Id != actorUid && u.IsActive)
-                            .Select(u => u.Id)
-                            .ToListAsync(ct);
-                        if (managers.Count > 0)
-                        {
-                            foreach (var mgrId in managers)
-                            {
-                                var mgr = await userManager.FindByIdAsync(mgrId.ToString());
-                                if (mgr is null) continue;
-                                var roles = await userManager.GetRolesAsync(mgr);
-                                if (!roles.Contains(AppRoles.DeptManager)) continue;
-
-                                await notifications.NotifyAsync(
-                                    mgrId,
-                                    NotificationType.ContractPhaseTransition,
-                                    title: $"Phiếu {evaluation.MaPhieu ?? evaluation.TenGoiThau} chờ TPB confirm",
-                                    description: $"NV {reviewerName} đã review phase {fromPhase}. Vui lòng vào confirm để workflow tiếp tục.",
-                                    href: $"/purchase-evaluations/{evaluation.Id}",
-                                    refId: evaluation.Id,
-                                    ct: ct);
-                            }
-                        }
-                    }
-                    catch { /* notification fail non-critical */ }
-
-                    await db.SaveChangesAsync(ct);
-                    return;
-                }
+            // Advance pointer
+            var nextIdx = currentIdx + 1;
+            if (nextIdx >= steps.Count)
+            {
+                // All steps done — terminal DaDuyet
+                evaluation.Phase = PurchaseEvaluationPhase.DaDuyet;
+                evaluation.CurrentWorkflowStepIndex = null;
+                evaluation.SlaDeadline = null;
+                await LogTransitionAsync(evaluation, fromPhase, PurchaseEvaluationPhase.DaDuyet, actorUserId, decision, comment, ct);
             }
+            else
+            {
+                evaluation.CurrentWorkflowStepIndex = nextIdx;
+                evaluation.SlaDeadline = dateTime.UtcNow.AddDays(7);
+                await LogTransitionAsync(evaluation, fromPhase, fromPhase, actorUserId, decision,
+                    $"Hoàn tất step {currentIdx + 1}/{steps.Count}, sang step {nextIdx + 1}", ct);
+            }
+            await db.SaveChangesAsync(ct);
+            return;
         }
 
-        evaluation.SlaWarningSent = false;
-        evaluation.Phase = targetPhase;
-
-        var sla = policy.PhaseSla.GetValueOrDefault(targetPhase);
-        evaluation.SlaDeadline = sla is null ? null : dateTime.UtcNow.Add(sla.Value);
-
-        db.PurchaseEvaluationApprovals.Add(new PurchaseEvaluationApproval
+        // Admin manual override (vd test cứng phase)
+        if (isAdmin)
         {
-            PurchaseEvaluationId = evaluation.Id,
-            FromPhase = fromPhase,
-            ToPhase = targetPhase,
-            ApproverUserId = actorUserId,
-            Decision = decision,
-            Comment = comment,
-            ApprovedAt = dateTime.UtcNow,
-        });
+            evaluation.Phase = targetPhase;
+            evaluation.SlaDeadline = targetPhase == PurchaseEvaluationPhase.ChoDuyet
+                ? dateTime.UtcNow.AddDays(7) : null;
+            await LogTransitionAsync(evaluation, fromPhase, targetPhase, actorUserId, decision, comment, ct);
+            await db.SaveChangesAsync(ct);
+            return;
+        }
 
-        // Resolve actor name for changelog
+        throw new ConflictException($"Transition {fromPhase} → {targetPhase} không hỗ trợ.");
+    }
+
+    private async Task LogTransitionAsync(
+        PurchaseEvaluation evaluation,
+        PurchaseEvaluationPhase fromPhase,
+        PurchaseEvaluationPhase toPhase,
+        Guid? actorUserId,
+        ApprovalDecision decision,
+        string? comment,
+        CancellationToken ct)
+    {
+        // Save Approval history (đã làm trong main flow — chỉ log Changelog ở đây)
         string? actorName = null;
         if (actorUserId is Guid uid)
         {
@@ -383,36 +214,34 @@ public class PurchaseEvaluationWorkflowService(
             PurchaseEvaluationId = evaluation.Id,
             EntityType = PurchaseEvaluationEntityType.Workflow,
             Action = ChangelogAction.Transition,
-            PhaseAtChange = targetPhase,
+            PhaseAtChange = toPhase,
             UserId = actorUserId,
             UserName = actorName ?? "Hệ thống",
-            Summary = $"Chuyển phase {fromPhase} → {targetPhase}",
+            Summary = $"Chuyển phase {fromPhase} → {toPhase}",
             ContextNote = comment,
         });
 
-        // Notify drafter
+        // Notify drafter on terminal states
         if (evaluation.DrafterUserId is Guid drafterId && drafterId != actorUserId)
         {
-            var title = targetPhase switch
+            var (title, type) = toPhase switch
             {
-                PurchaseEvaluationPhase.DaDuyet => $"Phiếu {evaluation.MaPhieu ?? evaluation.TenGoiThau} đã duyệt",
-                PurchaseEvaluationPhase.TuChoi => $"Phiếu {evaluation.TenGoiThau} bị từ chối",
-                _ => $"Phiếu {evaluation.TenGoiThau} chuyển phase mới",
-            };
-            var type = targetPhase switch
-            {
-                PurchaseEvaluationPhase.DaDuyet => NotificationType.ContractPublished,
-                PurchaseEvaluationPhase.TuChoi => NotificationType.ContractRejected,
-                _ => NotificationType.ContractPhaseTransition,
+                PurchaseEvaluationPhase.DaDuyet => ($"Phiếu {evaluation.MaPhieu ?? evaluation.TenGoiThau} đã duyệt",
+                                                    NotificationType.ContractPublished),
+                PurchaseEvaluationPhase.TuChoi => ($"Phiếu {evaluation.TenGoiThau} bị từ chối",
+                                                    NotificationType.ContractRejected),
+                PurchaseEvaluationPhase.DangSoanThao when fromPhase == PurchaseEvaluationPhase.ChoDuyet =>
+                    ($"Phiếu {evaluation.TenGoiThau} bị trả lại — vui lòng sửa và trình lại",
+                     NotificationType.ContractRejected),
+                _ => ($"Phiếu {evaluation.TenGoiThau} chuyển phase mới",
+                      NotificationType.ContractPhaseTransition),
             };
             await notifications.NotifyAsync(
                 drafterId, type, title,
-                description: $"{fromPhase} → {targetPhase}" + (string.IsNullOrWhiteSpace(comment) ? "" : $" · {comment}"),
+                description: $"{fromPhase} → {toPhase}" + (string.IsNullOrWhiteSpace(comment) ? "" : $" · {comment}"),
                 href: $"/purchase-evaluations/{evaluation.Id}",
                 refId: evaluation.Id,
                 ct: ct);
         }
-
-        await db.SaveChangesAsync(ct);
     }
 }