[CLAUDE] Infra: ContractWorkflowService N-stage logic mirror PE (Chunk C)

Refactor TransitionAsync mirror PurchaseEvaluationWorkflowService Mig 18
N-stage pattern:
- Reject branch: clear N-stage approval rows tại fromPhase (resume sẽ
  approve lại từ inner đầu)
- Load definition with InnerSteps eager + assign outer scope
- Department approval block split:
  * hasInnerSteps=true → N-stage logic:
    - Yêu cầu actor có DeptId + PositionLevel set (else throw 403)
    - Match firstPending (Order asc IsRequired) same dept + (exact level
      OR canBypass + level≥)
    - exact match: upsert 1 row InnerStepId, IsBypassed=false
    - bypass: batch upsert NV+PP+TP cùng dept ≤ actor (audit IsBypassed
      cho cấp dưới)
    - Recheck stillPending → BLOCK + log Approval/Changelog "duyệt cấp X
      (còn Y pending)"
    - All done → fall through phase transition
  * hasInnerSteps=false → Legacy 2-stage Mig 16 (giữ nguyên với
    InnerStepId=null filter)

Backward compat 100%: workflow Contract no InnerSteps configured →
service fallback legacy 2-stage NV.Review/TPB.Confirm. Tests 89 pass —
no regression.

Verify: dotnet build 0 error, dotnet test 89 pass.

Pending Chunk D: ContractNStageApprovalTests 6 test mirror PE pattern.

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

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

@@ -53,6 +53,15 @@ public class ContractWorkflowService(
         {
             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)
         {
@@ -64,14 +73,17 @@ public class ContractWorkflowService(
         // 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)
         {
-            var def = await db.WorkflowDefinitions.AsNoTracking()
+            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 = def is not null
-                ? WorkflowPolicyRegistry.FromDefinition(def)
+            policy = definition is not null
+                ? WorkflowPolicyRegistry.FromDefinition(definition)
                 : WorkflowPolicyRegistry.ForContract(contract);
         }
         else
@@ -108,10 +120,13 @@ public class ContractWorkflowService(
             }
         }
 
-        // ===== 2-stage department approval (Phase 9 — Migration 16) =====
-        // Mirror PE workflow service. NV thuộc dept review → BLOCK transition
-        // cho đến khi TPB cùng dept confirm. CanBypassReview cho NV → đẩy thẳng
-        // Confirm (skip Review). Skip với reject + resume + admin + system.
+        // ===== 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;
+
         if (decision == ApprovalDecision.Approve
             && targetPhase != ContractPhase.DangSoanThao
             && targetPhase != ContractPhase.TuChoi
@@ -120,21 +135,132 @@ public class ContractWorkflowService(
             && actorUserId is Guid actorUid)
         {
             var actor = await userManager.FindByIdAsync(actorUid.ToString());
-            if (actor?.DepartmentId is Guid deptId)
+
+            if (hasInnerSteps && currentStepDef is not null)
             {
+                // ===== N-stage logic (Mig 20) — mirror PE Mig 18 =====
+                if (actor?.DepartmentId is null || actor.PositionLevel is null)
+                {
+                    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
+                }
+            }
+            else if (actor?.DepartmentId is Guid deptId)
+            {
+                // ===== 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");
 
-                // Upsert: 1 row mỗi (ContractId, phase, dept, stage). UNIQUE index enforce.
                 var existing = await db.ContractDepartmentApprovals
                     .FirstOrDefaultAsync(a =>
                         a.ContractId == contract.Id
                         && a.PhaseAtApproval == (int)fromPhase
                         && a.DepartmentId == deptId
-                        && a.Stage == stage, ct);
+                        && a.Stage == stage
+                        && a.InnerStepId == null, ct);
                 if (existing is null)
                 {
                     db.ContractDepartmentApprovals.Add(new ContractDepartmentApproval
@@ -148,6 +274,7 @@ public class ContractWorkflowService(
                         Comment = comment,
                         ApprovedAt = dateTime.UtcNow,
                         IsBypassed = isBypassed,
+                        InnerStepId = null,
                     });
                 }
                 else
@@ -164,23 +291,23 @@ public class ContractWorkflowService(
                         a.ContractId == contract.Id
                         && a.PhaseAtApproval == (int)fromPhase
                         && a.DepartmentId == deptId
-                        && a.Stage == ApprovalStage.Confirm, ct);
+                        && a.Stage == ApprovalStage.Confirm
+                        && a.InnerStepId == null, ct);
 
                 if (!hasConfirm)
                 {
-                    // NV review xong, chưa có TPB confirm → BLOCK phase transition.
                     db.ContractApprovals.Add(new ContractApproval
                     {
                         ContractId = contract.Id,
                         FromPhase = fromPhase,
-                        ToPhase = fromPhase,    // không đổi phase
+                        ToPhase = fromPhase,
                         ApproverUserId = actorUid,
                         Decision = ApprovalDecision.Approve,
                         Comment = $"[Review NV] {comment ?? ""}",
                         ApprovedAt = dateTime.UtcNow,
                     });
 
-                    string? reviewerName = (actor.FullName ?? actor.Email);
+                    string? reviewerName = actor.FullName ?? actor.Email;
                     db.ContractChangelogs.Add(new ContractChangelog
                     {
                         ContractId = contract.Id,