[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  no longer applicable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.Application/Contracts/WorkflowAdminFeatures.cs

@@ -17,26 +17,19 @@ public record WorkflowStepApproverDto(
     string AssignmentValue,
     string? DisplayName);   // resolved role label or user fullName
 
-// Mig 20 — N-stage approval inner step level con (mirror PE Mig 18)
-public record WorkflowStepInnerStepDto(
-    Guid Id,
-    int Order,
-    Guid DepartmentId,
-    string? DepartmentName,
-    int PositionLevel,        // 1=NV, 2=PP, 3=TP
-    string? Name,
-    int? SlaDays,
-    bool IsRequired);
-
+// Mig 21 — flat workflow step. Mỗi step = 1 (Phòng × Cấp + Approvers users)
+// sequential. Service iterate theo Order, advance Contract.CurrentWorkflowStepIndex.
 public record WorkflowStepDto(
     Guid Id,
     int Order,
-    int Phase,
+    int Phase,                  // [DEPRECATED post-Mig 21] dùng ChoDuyet=10 cho new
     string PhaseLabel,
-    string Name,
+    string Name,                // "Phòng A — Cấp 1"
     int? SlaDays,
-    List<WorkflowStepApproverDto> Approvers,
-    List<WorkflowStepInnerStepDto> InnerSteps);
+    Guid? DepartmentId,         // Mig 21
+    string? DepartmentName,     // resolved display
+    int? PositionLevel,         // Mig 21 — 1=NV, 2=PP, 3=TP
+    List<WorkflowStepApproverDto> Approvers);
 
 public record WorkflowDefinitionDto(
     Guid Id,
@@ -96,15 +89,15 @@ public class GetWorkflowAdminOverviewQueryHandler(
         var definitions = 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))
             .OrderByDescending(d => d.Version)
             .ToListAsync(ct);
 
-        // Resolve dept names cho InnerStep.DepartmentName display (Mig 20)
+        // Resolve dept names cho step.DepartmentId display (Mig 21)
         var deptIds = definitions
-            .SelectMany(d => d.Steps).SelectMany(s => s.InnerSteps)
-            .Select(i => i.DepartmentId).Distinct().ToList();
+            .SelectMany(d => d.Steps)
+            .Where(s => s.DepartmentId != null)
+            .Select(s => s.DepartmentId!.Value)
+            .Distinct().ToList();
         var deptNames = deptIds.Count == 0
             ? new Dictionary<Guid, string>()
             : await db.Departments.AsNoTracking()
@@ -151,19 +144,13 @@ public class GetWorkflowAdminOverviewQueryHandler(
                 PhaseLabels.GetValueOrDefault(s.Phase, s.Phase.ToString()),
                 s.Name,
                 s.SlaDays,
+                s.DepartmentId,
+                s.DepartmentId != null ? deptNames.GetValueOrDefault(s.DepartmentId.Value) : null,
+                s.PositionLevel != null ? (int?)s.PositionLevel : null,
                 s.Approvers.Select(a => new WorkflowStepApproverDto(
                     (int)a.Kind,
                     a.AssignmentValue,
-                    ResolveDisplay(a, userNames))).ToList(),
-                s.InnerSteps.OrderBy(i => i.Order).Select(i => new WorkflowStepInnerStepDto(
-                    i.Id,
-                    i.Order,
-                    i.DepartmentId,
-                    deptNames.GetValueOrDefault(i.DepartmentId),
-                    (int)i.PositionLevel,
-                    i.Name,
-                    i.SlaDays,
-                    i.IsRequired)).ToList()
+                    ResolveDisplay(a, userNames))).ToList()
             )).ToList());
 
         var types = Enum.GetValues<ContractType>()
@@ -193,23 +180,16 @@ public class GetWorkflowAdminOverviewQueryHandler(
 
 public record CreateWorkflowStepApproverInput(int Kind, string AssignmentValue);
 
-// Mig 20 — Inner step input cho designer N-stage. InnerSteps optional empty
-// list → service fallback 2-stage Review/Confirm logic legacy Mig 16.
-public record CreateWorkflowStepInnerStepInput(
-    int Order,
-    Guid DepartmentId,
-    int PositionLevel,        // 1=NV, 2=PP, 3=TP
-    string? Name,
-    int? SlaDays,
-    bool IsRequired);
-
+// Mig 21 — flat workflow step input. DeptId + PositionLevel = Phòng × Cấp.
+// Phase auto-assign ChoDuyet=10 cho new definitions (legacy phase-specific deprecated).
 public record CreateWorkflowStepInput(
     int Order,
-    int Phase,
+    int Phase,                  // [DEPRECATED] caller có thể truyền 10=ChoDuyet hoặc legacy enum value
     string Name,
     int? SlaDays,
-    List<CreateWorkflowStepApproverInput> Approvers,
-    List<CreateWorkflowStepInnerStepInput>? InnerSteps = null);
+    Guid? DepartmentId,         // Mig 21
+    int? PositionLevel,         // Mig 21 — 1=NV, 2=PP, 3=TP
+    List<CreateWorkflowStepApproverInput> Approvers);
 
 public record CreateWorkflowDefinitionCommand(
     ContractType ContractType,
@@ -233,25 +213,18 @@ public class CreateWorkflowDefinitionCommandValidator : AbstractValidator<Create
         RuleForEach(x => x.Steps).ChildRules(step =>
         {
             step.RuleFor(s => s.Order).GreaterThanOrEqualTo(1);
-            step.RuleFor(s => s.Phase).InclusiveBetween(1, 9);
+            step.RuleFor(s => s.Phase).InclusiveBetween(1, 99);   // Mig 21 accept ChoDuyet=10
             step.RuleFor(s => s.Name).NotEmpty().MaximumLength(200);
             step.RuleFor(s => s.SlaDays).GreaterThanOrEqualTo(0)
                 .When(s => s.SlaDays != null);
+            step.RuleFor(s => s.PositionLevel).InclusiveBetween(1, 3)
+                .When(s => s.PositionLevel != null)
+                .WithMessage("PositionLevel: 1=NV, 2=PP, 3=TP.");
             step.RuleForEach(s => s.Approvers).ChildRules(app =>
             {
                 app.RuleFor(a => a.Kind).InclusiveBetween(1, 2);
                 app.RuleFor(a => a.AssignmentValue).NotEmpty().MaximumLength(100);
             });
-            step.RuleForEach(s => s.InnerSteps!).ChildRules(inner =>
-            {
-                inner.RuleFor(i => i.Order).GreaterThanOrEqualTo(1);
-                inner.RuleFor(i => i.DepartmentId).NotEmpty();
-                inner.RuleFor(i => i.PositionLevel).InclusiveBetween(1, 3)
-                    .WithMessage("PositionLevel: 1=NV, 2=PP, 3=TP.");
-                inner.RuleFor(i => i.Name).MaximumLength(200);
-                inner.RuleFor(i => i.SlaDays).GreaterThanOrEqualTo(0)
-                    .When(i => i.SlaDays != null);
-            }).When(s => s.InnerSteps != null);
         });
     }
 }
@@ -291,20 +264,13 @@ public class CreateWorkflowDefinitionCommandHandler(IApplicationDbContext db)
                     Phase = (ContractPhase)s.Phase,
                     Name = s.Name,
                     SlaDays = s.SlaDays,
+                    DepartmentId = s.DepartmentId,
+                    PositionLevel = s.PositionLevel != null ? (PositionLevel)s.PositionLevel : null,
                     Approvers = s.Approvers.Select(a => new WorkflowStepApprover
                     {
                         Kind = (WorkflowApproverKind)a.Kind,
                         AssignmentValue = a.AssignmentValue,
                     }).ToList(),
-                    InnerSteps = (s.InnerSteps ?? new()).OrderBy(i => i.Order).Select(i => new WorkflowStepInnerStep
-                    {
-                        Order = i.Order,
-                        DepartmentId = i.DepartmentId,
-                        PositionLevel = (PositionLevel)i.PositionLevel,
-                        Name = i.Name,
-                        SlaDays = i.SlaDays,
-                        IsRequired = i.IsRequired,
-                    }).ToList(),
                 })
                 .ToList(),
         };