[CLAUDE] Docs: Chunk E — chốt Session 21 turn 4 F1+F2+F3 PE Workflow advanced options (Mig 28)

Update docs theo rule §6.5 KEEP narrative:

- `docs/database/schema-diagram.md §14` title "Mig 22-28, S17-21" + thêm 6
  column Allow* inline trong Core ApprovalWorkflows block (inline comment
  F1/F2/F3 mapping). Bonus: 3 bảng (Steps + Levels) unchanged.

- `docs/STATUS.md` Last updated S21 t4 + count 27→28 mig (Mig 28 advanced
  options 6 column). UAT defer test count unchanged 84 (test-after-uat candidate
  bundle Plan C carry).

- `docs/HANDOFF.md` Insert TL;DR S21 t4 đầy đủ (trước S21 t3):
  - Q&A clarify 2 lượt chốt scope (F1 cả 2 mode admin, F1 Assignee runtime,
    F2 chỉ Cấp cuối, F3 Section 2 only, F2+F3 admin tick, F3 mọi approver
    active, test-after UAT)
  - 5 chunk narrative đầy đủ A schema → B BE → C FE Admin → D FE eOffice → E Docs
  - Pattern reusable: backward-compat option flags, boundary helper extension
  - State table cumulative + pending Plan C test-after catch-up

- NEW session log `docs/changelog/sessions/2026-05-13-1200-s21-turn4-pe-workflow-advanced-options.md`:
  - Trigger + Q&A 2 lượt
  - 5 chunk narrative chi tiết với code snippets
  - Pattern reusable 5 lessons learned
  - References file paths + spec context

Stats cumulative S21 t4:
- 28 mig (+1) · 59 tables · ~143 endpoints (+1) · 34 FE pages · 84 test pass
  (UAT defer test-after §7) · 45 gotcha unchanged · 17 memory · 6 skills
- 5 commits S21 t4 cumulative ready push remote

Pending: bro confirm push `0a3b747..HEAD` 8 commits ahead (S21 t3 + S21 t4).

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

docs/HANDOFF.md

@@ -1,8 +1,264 @@
 # HANDOFF — Brief 5 phút cho session tiếp theo
 
-**Last updated:** 2026-05-12 (Session 21 turn 2 — **🎯 RAG Hybrid setup planning + Cách A validation deep dive. 2 commit (`1f8e9af` plan save 1223 LOC + this chốt). KHÔNG implement, plan only — defer chờ bro confirm 5 dự án future. Decision chốt: Cách A defensive (giữ blanket 120K em main + RAG retrieve) over Cách B aggressive (cắt 60-70% blanket). Industry-validated cross 4 Anthropic blog + 5 community tools (Cursor/Continue/Cline/Aider). Stack: Voyage-3-large + Qdrant + FastMCP + Streamlit dashboard. Multi-agent cost reality: 4 agents → ~520K cumulative blanket → heavy session ~560K (Cách A) vs ~700K (lazy). 3-layer pattern Phase 1-3 rollout (embeddings + BM25 + reranking, ~70% → ~92% recall). Stats: +1 memory entry (`feedback_rag_hybrid_pattern`) +1 plan file (`rag-setup-plan.md` 1500 LOC). Sub-agents vẫn 4 seeds-only, em main solo session.**)
+**Last updated:** 2026-05-13 1200 (Session 21 turn 4 — **🎯 F1+F2+F3 PE Workflow advanced options (Mig 28) — 5 chunk per-commit `0294693` (A schema) → `c56024b` (B BE) → `a508564` (C FE Admin) → `d27caaf` (D FE eOffice) → this (E Docs). **F1** 4 mode Trả lại admin tick stick (1 Cấp / 1 Bước / Người chỉ định / Người soạn thảo) — 3 mode đầu giữ Phase=ChoDuyet lùi pointer (peer review chain), mode Drafter giữ Phase=TraLai clear pointer (S17 backward compat). **F2** Drafter skip thẳng Cấp cuối — workflow tick + Workspace checkbox dynamic. **F3** Approver edit Section 2 (Hạng mục/NCC/Báo giá) khi workflow tick + actor match CurrentLevel.ApproverUserId + audit ghi PurchaseEvaluationChangelog. Mig 28 thêm 6 bit column lên `ApprovalWorkflows` (DEFAULT 1 cho AllowReturnToDrafter backward compat, 5 còn lại 0). BE Service extend signature 3 optional param (returnMode/returnTargetUserId/skipToFinal). Helper `EnsureEditableForDetailsAsync` mới gating Detail/Quote/Supplier CRUD theo Drafter scope OR F3 Approver scope + audit changelog Update/Delete (trước đây silent). FE Admin Designer "Cấu hình nâng cao" section 6 checkbox 3 group. FE eOffice 3 changes mirror 2 app. UAT mode skip dotnet test mỗi chunk, npm build × 2 app pass mỗi chunk. CHƯA push remote — chờ bro confirm.**)
+**S21 turn 3:** 2026-05-12 2100 (Session 21 turn 3 — **🔴 BUG FIX CRITICAL "Trả về nhưng hệ thống vẫn duyệt" PE workflow (gotcha #45 mới). 3 chunk per-commit: `de00887` (BE Chunk A guard + 3 test) + `4b29d00` (FE Chunk B fix 2 app mirror) + this Chunk C Docs. Root: `PeWorkflowPanel.tsx` `isReject` payload (L64-66) thiếu nhánh TraLai → button "← Trả lại" gửi `decision: 1` (Approve) thay vì `2` (Reject) khi target=TraLai(98) → BE skip Reject branch → enter APPROVE STEP → `ApproveV2Async` UPSERT opinion "đã duyệt" + advance Cấp tiếp theo. Inconsistency phụ: dialog `isSendBack` (L247-248) cùng pattern thiếu TraLai → dialog title sai `'✓ Duyệt → Trả lại'` + KHÔNG amber warning. Severity CRITICAL — data integrity issue khó rollback (BE đã `SaveChangesAsync`). Test-before §7 BẮT BUỘC: viết test reproduce → confirm FAIL (BE đi sâu vào ApproveV2Async throw "Phiếu chưa pin workflow") → thêm BE guard early throw ConflictException khi `target ∈ {TraLai, TuChoi} && decision != Reject` → confirm PASS. 3 regression test (Throws TraLai+Approve, Throws TuChoi+Approve consistency, happy path Reject+TraLai). Tổng `dotnet test SolutionErp.slnx` 84 PASS (58 Domain + 26 Infra = +3 from 81 baseline). `npm run build` × 2 app pass. Stats: 27 mig (no change) · 59 tables · ~142 endpoints · 34 FE pages · **84 test (+3)** · **45 gotcha (+1 #45)** · 17 memory · 6 skills · 4 sub-agents seeds-only. Em main solo S21 t3 — bug fix reasoning chain cross BE/FE Implementer REFUSE per multi-agent rule (decision tree: tightly coupled BE+FE+test). CHƯA push remote — chờ bro confirm sau Chunk C wrap.**)
+**S21 turn 2:** 2026-05-12 1800 (Session 21 turn 2 — **🎯 RAG Hybrid setup planning + Cách A validation deep dive. 2 commit (`1f8e9af` plan save 1223 LOC + this chốt). KHÔNG implement, plan only — defer chờ bro confirm 5 dự án future. Decision chốt: Cách A defensive (giữ blanket 120K em main + RAG retrieve) over Cách B aggressive (cắt 60-70% blanket). Industry-validated cross 4 Anthropic blog + 5 community tools (Cursor/Continue/Cline/Aider). Stack: Voyage-3-large + Qdrant + FastMCP + Streamlit dashboard. Multi-agent cost reality: 4 agents → ~520K cumulative blanket → heavy session ~560K (Cách A) vs ~700K (lazy). 3-layer pattern Phase 1-3 rollout (embeddings + BM25 + reranking, ~70% → ~92% recall). Stats: +1 memory entry (`feedback_rag_hybrid_pattern`) +1 plan file (`rag-setup-plan.md` 1500 LOC). Sub-agents vẫn 4 seeds-only, em main solo session.**)
 **S21 turn 1:** 2026-05-12 0030 (Session 21 turn 1 — **🎯 Add con thứ 4 cicd-monitor (Path A — post-deploy verifier). 1 commit `f1c61c9` pushed `36e21c8..f1c61c9 main -> main`. CI skipped per path filter (3 file `.md`). Cost reality update: ~750K spawn (3 → 4 agents) · ~1.35M heavy / ~700K optimized. Stats: 4 sub-agents seeds-only · 16 memory · 27 mig · 59 tables · ~142 endpoints · 81 test · 44 gotcha · 6 skills unchanged. KHÔNG flush 3 agent MEMORY.md (chưa spawn work — em main solo). Trial Week 1 kick-off S21 turn 2+ Plan B Contract V2 wire mirror PE pattern.**)
 
+## TL;DR Session 21 turn 4 — F1+F2+F3 PE Workflow advanced options (Mig 28)
+
+User request 3 tính năng mới trong PE V2 Workflow:
+- **F1** 4 mode Trả lại admin stick: 1 Cấp / 1 Bước / Người chỉ định / Người soạn thảo
+- **F2** Drafter gửi thẳng Cấp cuối (skip mọi Bước/Cấp trung gian)
+- **F3** Approver chỉnh sửa Section 2 (Hạng mục + NCC + Báo giá) khi đang duyệt
+
+### Q&A clarify chốt scope (2 lượt AskUserQuestion)
+
+- **F1 "1 bậc"** = cả 2 mode (admin chọn 1 Cấp HOẶC 1 Bước HOẶC cả 2 stick)
+- **F1 "Người chỉ định"** = Approver pick runtime từ list NV đã ký (PE.LevelOpinions)
+- **F1 behavior** = 3 mode đầu giữ Phase=ChoDuyet lùi pointer (peer review chain). Mode Drafter giữ Phase=TraLai S17 fallback.
+- **F2 skip** = chỉ skip tới Level cuối (CEO) — Dropdown 2 option "Gửi tuần tự" vs "Gửi thẳng Cấp cuối"
+- **F2+F3 admin enable** = cả 2 cần admin tick per workflow (audit nghiêm)
+- **F3 approver perm** = mọi approver Cấp đang active (currentLevel match)
+- **F3 scope** = Section 2 only (Hạng mục + NCC + Báo giá), KHÔNG đụng PE Header, KHÔNG reset workflow
+- **Test** = test-after UAT default Phase 9 (skip dotnet test mỗi chunk, npm build × 2 app pass)
+
+### Chunk A — Mig 28 + Domain (`0294693`)
+
+`ApprovalWorkflow.cs` thêm 6 bool field:
+- `AllowReturnOneLevel` / `AllowReturnOneStep` / `AllowReturnToAssignee` (default false)
+- `AllowReturnToDrafter` (default **TRUE** — backward compat S17)
+- `AllowDrafterSkipToFinal` / `AllowApproverEditDetails` (default false)
+
+EF config `ApprovalWorkflowConfiguration` thêm 6 `HasDefaultValue` match Mig 28 DEFAULT.
+
+Mig 28 `AddAdvancedOptionsToApprovalWorkflows`:
+- 6 AddColumn bit NOT NULL DEFAULT 0/1
+- 3-file rule complete (mig.cs + Designer.cs + Snapshot.cs)
+- Apply LocalDB Dev + Design
+
+### Chunk B — BE Service + handlers + DTOs (`c56024b`)
+
+**Service interface + impl** `TransitionAsync` thêm 3 optional param (backward compat):
+- `WorkflowReturnMode? returnMode` (enum {OneLevel=1, OneStep=2, Assignee=3, Drafter=4})
+- `Guid? returnTargetUserId` (required khi mode=Assignee)
+- `bool skipToFinal`
+
+REJECT branch extend với helper `ApplyReturnModeAsync` switch 4 mode:
+- OneLevel: lùi 1 Cấp cùng Step. Bước 1 Cấp 1 → fallback Drafter.
+- OneStep: lùi sang Bước trước Cấp cuối. Bước 1 → fallback Drafter.
+- Assignee: tìm Step+Level match `ApproverUserId == returnTargetUserId`.
+- Drafter: Phase=TraLai clear pointer (S17 behavior).
+- 3 mode đầu giữ ChoDuyet + reset SLA 7d.
+- Admin bypass workflow.Allow* flag check.
+- Non-admin → throw ConflictException nếu flag disabled.
+
+DRAFTER trình branch extend với F2 skipToFinal:
+- Workflow.AllowDrafterSkipToFinal required (non-admin)
+- Set CurrentWorkflowStepIndex = Steps.Count-1 + CurrentApprovalLevelOrder = max Level
+- Audit comment append "[Drafter gửi thẳng Cấp cuối]"
+
+**Helper edit guard** `EnsureEditableForDetailsAsync` mới (PurchaseEvaluationDraftGuard class):
+- Drafter scope: DangSoanThao OR TraLai
+- F3 Approver scope: ChoDuyet + workflow.AllowApproverEditDetails + actor match CurrentLevel.ApproverUserId
+- Admin bypass workflow flag check
+
+**8 handler switch** sang helper mới + inject ICurrentUser khi cần:
+- Detail Add/Update/Delete + Quote Upsert/Delete (5 handler — replace EnsureDraftAsync)
+- Supplier Add/Update/Remove (3 handler — bonus security fix, trước đây hoàn toàn KHÔNG có phase guard!)
+- Update/Delete handler trước đây silent → thêm changelog `PhaseAtChange + UserId + Summary` (append `[Approver edit khi đang duyệt]` khi phase=ChoDuyet)
+
+**Command DTO + DTOs**:
+- `TransitionPurchaseEvaluationCommand` +3 optional field
+- `ApprovalWorkflowOptionsDto` NEW sub-record (6 Allow* flag)
+- `PurchaseEvaluationDetailBundleDto` +WorkflowOptions field
+- `AwDefinitionDto` +6 Allow* (admin Designer GET)
+- `CreateAwDefinitionCommand` +6 Allow* param (admin Designer POST)
+
+### Chunk C — FE Admin Designer (`a508564`)
+
+`ApprovalWorkflowsV2Page.tsx` Designer modal thêm section "Cấu hình nâng cao" 3 sub-group:
+
+1. Mode Trả lại 4 checkbox:
+   - Trả về 1 Cấp trước (peer review chain trong cùng Bước)
+   - Trả về 1 Bước trước (Cấp cuối Bước trước nhận lại)
+   - Trả về Người chỉ định (pick runtime từ NV đã ký)
+   - Trả về Người soạn thảo (default checked = backward compat S17)
+
+2. Drafter skip: 1 checkbox "Cho phép Drafter gửi thẳng Cấp cuối"
+
+3. Approver edit: 1 checkbox "Cho phép Approver chỉnh sửa Section 2"
+
+Styling: container amber-50/30 border distinct với Steps section. Helper text [10px] dưới label. Headers uppercase tracking.
+
+DTO types + state defaults từ cloneFrom (giữ config version trước) hoặc S17 fallback (chỉ AllowReturnToDrafter=true). POST body propagate 6 flag → BE Create handler set entity.
+
+fe-user KHÔNG mirror (Designer admin-only).
+
+### Chunk D — FE eOffice (`d27caaf`) mirror 2 app
+
+Types `purchaseEvaluation.ts`:
+- `ApprovalWorkflowOptions` type
+- `WorkflowReturnMode` const-object
+- `PeDetailBundle` +workflowOptions field
+
+`PeWorkflowPanel.tsx` F1 Trả lại radio picker:
+- State `returnMode` (default Drafter) + `returnTargetUserId`
+- Dialog Trả lại render 1-4 radio mode enabled theo wfOptions.Allow*
+- Assignee mode → submodal Select pick từ levelOpinions (NV đã ký), dedupe by userId
+- Banner amber rounded dưới mô tả hành vi mode chọn
+- Mutation payload +returnMode +returnTargetUserId khi isTraLaiAction
+
+`PeDetailTabs.tsx` F2 Drafter skip:
+- State `skipToFinal` + `allowSkipToFinal` từ workflowOptions
+- submitForApproval mutationFn accept opts.skipToFinal
+- Workspace action bar: checkbox violet "Gửi thẳng Cấp cuối (skip trung gian)" conditional
+- Confirm dialog message + button label dynamic theo skipToFinal
+
+`PeDetailTabs.tsx` F3 Approver edit Section 2:
+- useAuth import + compute `approverEditMode` (phase=ChoDuyet + workflowOptions.allowApproverEditDetails + actor match)
+- `itemsReadOnly = readOnly && !approverEditMode` → ItemsTab nhận
+- Banner violet "ⓘ Bạn được phép chỉnh sửa..." khi approverEditMode + readOnly (Duyệt menu)
+- InfoTab / NccSelectorRow / BudgetFieldRow GIỮ strict isEditablePhase (Header + Section 3, KHÔNG trong F3 scope)
+
+### Chunk E — Docs (this commit)
+
+- `docs/database/schema-diagram.md §14` cập nhật title "Mig 22-28, S17-21" + thêm 6 column Allow* trong Core block với inline comment F1/F2/F3
+- `docs/STATUS.md` Last updated S21 t4 + count 27→28 mig + UAT defer test count unchanged 84
+- `docs/HANDOFF.md` TL;DR S21 t4 đầy đủ (file này)
+- `docs/changelog/sessions/2026-05-13-1200-s21-turn4-pe-workflow-advanced-options.md` session log
+
+### State chốt S21 turn 4
+
+| Metric | Trước (S21 t3) | Sau (S21 t4) | Δ |
+|---|---|---|---|
+| DB tables | 59 | 59 | 0 |
+| **Migrations** | 27 | **28** | **+1** (Mig 28 6 column Allow*) |
+| Endpoints | ~142 | ~143 | +1 (extend transitions body) |
+| FE pages | 34 | 34 | 0 (Designer extend section) |
+| **Unit tests** | 84 | **84** | 0 (UAT defer test-after §7) |
+| Gotchas | 45 | 45 | 0 |
+| Memory entries | 17 | 17 | 0 |
+| Skills | 6 | 6 | 0 |
+| Sub-agents | 4 seeds-only | 4 seeds-only | 0 |
+| **Commits S21 t4** | — | **5** | (`0294693` → `c56024b` → `a508564` → `d27caaf` → this) |
+
+### Pending — Test-after (Plan C carry)
+
+Per `feedback_uat_skip_verify` Phase 9 default: viết test sau UAT 2-3 lần ổn.
+Test scope candidate (test-after-uat commit riêng):
+- Service `ApplyReturnModeAsync` 4 mode happy path (OneLevel/OneStep/Assignee/Drafter)
+- Service skipToFinal happy path + AllowDrafterSkipToFinal=false → ConflictException
+- `EnsureEditableForDetailsAsync` 3 scenario: Drafter scope / Approver match / Approver mismatch → Forbidden
+
+Bundle với Plan C existing (test #44 silent 403 + test V2 ApproveV2Async + Mig 25/27 PATCH).
+
+---
+
+## TL;DR Session 21 turn 3 — Bug fix CRITICAL "Trả về nhưng hệ thống vẫn duyệt" (gotcha #45)
+
+User UAT 2026-05-12 21:00 screenshot button labeled `← Trả lại` trong PE Workflow Panel (menu "Duyệt"), mô tả hành vi: nhấn vào nhưng phiếu KHÔNG về phase TraLai — ngược lại tiến qua Cấp tiếp theo. User mô tả: "Trả về nhưng hệ thống vẫn duyệt".
+
+### Diagnose (em main solo, no agent spawn)
+
+3 chỗ inconsistency cùng pattern trong `PeWorkflowPanel.tsx` (× 2 app fe-admin + fe-user):
+
+| # | Location | Logic | Bug? |
+|---|---|---|---|
+| 1 | L205-207 button `isSendBack` | include TraLai → label `← Trả lại` ĐÚNG | ✅ no bug |
+| 2 | L64-66 payload `isReject` | thiếu nhánh TraLai → gửi `decision: 1` (Approve) | 🔴 BUG ROOT |
+| 3 | L247-248 dialog `isSendBack` | thiếu nhánh TraLai → dialog title fallback `'✓ Duyệt → Trả lại'` + no amber warning | 🔴 BUG phụ |
+
+BE `PurchaseEvaluationWorkflowService.TransitionAsync`:
+- L51 `if (decision == Reject)` branch → đúng cho decision=Reject.
+- L97 `APPROVE STEP` branch khi decision=Approve + fromPhase=ChoDuyet → ApproveV2Async UPSERT opinion + advance Cấp.
+- → FE gửi `decision=1` (do bug `isReject`) → BE đi vào nhánh APPROVE thay vì REJECT → phiếu approve mặc dù user định trả lại.
+
+### Chunk A — BE defense-in-depth + 3 regression test (`de00887`)
+
+**Test-before §7 BẮT BUỘC:** Viết test reproduce bug TRƯỚC fix.
+
+```csharp
+// Sau line 48 (set isAdmin/isSystem), trước REJECT branch (L51)
+if ((targetPhase == PurchaseEvaluationPhase.TraLai
+        || targetPhase == PurchaseEvaluationPhase.TuChoi)
+    && decision != ApprovalDecision.Reject)
+{
+    throw new ConflictException(
+        $"Transition tới {targetPhase} BẮT BUỘC decision=Reject (nhận {decision}). " +
+        "Báo lỗi caller — payload mismatch giữa target phase và decision.");
+}
+```
+
+Boundary protection cho mọi caller tương lai (API client / mobile / cron retry). Guard KHÔNG xoá khi FE fix — defense-in-depth.
+
+3 test file `tests/SolutionErp.Infrastructure.Tests/Services/PurchaseEvaluationWorkflowServiceGuardTests.cs`:
+- `TransitionAsync_TargetTraLai_WithApproveDecision_Throws_AndDoesNotMutateState` — reproduce bug, expect `ConflictException` "*TraLai*Reject*"
+- `TransitionAsync_TargetTuChoi_WithApproveDecision_Throws_AndDoesNotMutateState` — consistency cover TuChoi
+- `TransitionAsync_TargetTraLai_WithRejectDecision_SetsPhaseTraLai` — happy path control (Reject branch vẫn đúng)
+
++ `NoOpNotificationService` stub reusable cho future PE service tests (avoid `INotificationService` real DI complexity).
+
+Run test → 2 FAIL (reproduce bug, BE đi sâu vào ApproveV2Async throw "Phiếu chưa pin workflow") + 1 PASS (happy path). Thêm BE guard → 3 PASS. Tổng `dotnet test SolutionErp.slnx` 84 PASS (+3 from 81 baseline).
+
+### Chunk B — FE fix mirror 2 app (`4b29d00`)
+
+3 chỗ × 2 app = 6 edits:
+
+```typescript
+// Chỗ 1: isReject payload (L64-66)
+const isReject = target === PurchaseEvaluationPhase.TuChoi
+  || (target === PurchaseEvaluationPhase.DangSoanThao
+      && evaluation.phase !== PurchaseEvaluationPhase.DangSoanThao)
+  || (target === PurchaseEvaluationPhase.TraLai             // ← THÊM
+      && evaluation.phase !== PurchaseEvaluationPhase.TraLai)
+
+// Chỗ 3: dialog isSendBack (L247-248)
+const isSendBack = (target === PurchaseEvaluationPhase.DangSoanThao
+                    || target === PurchaseEvaluationPhase.TraLai)   // ← THÊM
+  && evaluation.phase !== PurchaseEvaluationPhase.DangSoanThao
+  && evaluation.phase !== PurchaseEvaluationPhase.TraLai             // ← THÊM
+```
+
+Chỗ 2 (button label `isSendBack` L205-207) đã đúng từ S17, KHÔNG đụng.
+
+Verify: `npm run build` × 2 app pass (fe-user 17.91s + fe-admin 6.71s, 0 TS6 err).
+
+### Chunk C — Docs (this commit)
+
+- `docs/gotchas.md` +#45 PE button label vs decision payload mismatch (~120 dòng narrative + 2 commit cross-ref + pattern reusable + phòng tránh tương lai)
+- `docs/gotchas.md` checklist debug +entry 22 quick lookup
+- `docs/STATUS.md` Last updated S21 t3 + count 81→84 test + 44→45 gotcha
+- `docs/HANDOFF.md` TL;DR S21 t3 narrative đầy đủ (file này)
+- `docs/changelog/sessions/2026-05-12-2100-s21-turn3-fix-tra-lai-bug45.md` session log mới
+
+### Pending (carry from S21 turn 2)
+
+Plans A-I unchanged. Plan C1 (test regression gotcha #44 silent 403 S18) vẫn còn nợ — không bundle với S21 t3 fix (scope khác, ưu tiên unblock UAT bug critical trước).
+
+### Audit cadence
+
+- Lần gần nhất: 2026-05-04 manual trễ 4 ngày
+- Lần kế: **2026-06-01** combined audit
+- Drift sau S21 t3: 44→45 gotcha (+1) + 81→84 test (+3) + 17→17 memory (no new) + 6 skills unchanged
+
+### State chốt S21 turn 3
+
+| Metric | Trước (S21 t2) | Sau (S21 t3) | Δ |
+|---|---|---|---|
+| DB tables | 59 | 59 | 0 |
+| Migrations | 27 | 27 | 0 |
+| Endpoints | ~142 | ~142 | 0 |
+| FE pages | 34 | 34 | 0 |
+| **Unit tests** | 81 | **84** | **+3** (PE guard) |
+| **Gotchas** | 44 | **45** | **+1** (#45) |
+| Memory entries | 17 | 17 | 0 |
+| Skills | 6 | 6 | 0 |
+| Sub-agents | 4 seeds-only | 4 seeds-only | 0 |
+| **Commits S21 t3** | — | **3** | (`de00887` + `4b29d00` + this) |
+
+---
+
 ## TL;DR Session 21 turn 2 — RAG Hybrid setup planning (Cách A chốt + 3-layer pattern)
 
 User clarify 5 dự án future > 1M MD tokens → cuộc thảo luận deep ~15 turn về RAG infrastructure. Em main solo (no SOLUTION_ERP sub-agent spawn), delegate 2 lần claude-code-guide agent research Anthropic + community practice.

docs/STATUS.md

@@ -2,13 +2,15 @@
 
 > **Update rule:** trước khi bắt đầu 1 task → ghi row vào `🔥 In Progress`. Xong → chuyển sang `✅ Recently Done`.
 
-**Last updated:** 2026-05-12 1800 (Session 21 turn 2 — **🎯 RAG Hybrid setup planning + Cách A validation deep dive. 2 commit (`1f8e9af` plan save 1223 LOC + this chốt). Em main solo (no SOLUTION_ERP sub-agent spawn), delegate claude-code-guide × 2 research Anthropic + community practice. Decision chốt: Cách A defensive (giữ blanket 120K em main + RAG retrieve supplement) over Cách B aggressive (cắt 60-70% blanket). Industry-validated cross 4 Anthropic blog + 5 community tools (Cursor/Continue/Cline/Aider all hybrid). Stack: Voyage-3-large + Qdrant local + FastMCP Python + Streamlit dashboard 7 pages + SQLite event log. Multi-agent cost reality: 4 agents → ~520K cumulative blanket → heavy session ~560K (Cách A) vs ~700K (lazy), saving -20%. 3-layer pattern Phase 1-3 rollout (Layer 1 vector → Layer 2 +BM25 → Layer 3 +reranking, recall ~70% → ~92%). Stats: +1 memory entry (`feedback_rag_hybrid_pattern.md`) +1 plan file (`rag-setup-plan.md` 1500 LOC final). 4 sub-agents vẫn seeds-only. Plan I NEW deferred chờ bro confirm 5 dự án path + stack + Voyage API key + disk cleanup 5-8GB.**)
+**Last updated:** 2026-05-13 1200 (Session 21 turn 4 — **🎯 F1+F2+F3 PE Workflow advanced options (Mig 28) — 5 chunk per-commit `0294693`→`c56024b`→`a508564`→`d27caaf`→this Chunk E Docs. **F1** 4 mode Trả lại admin tick: "1 Cấp / 1 Bước / Người chỉ định / Người soạn thảo" — 3 mode đầu giữ Phase=ChoDuyet lùi pointer (peer review chain), mode Drafter giữ Phase=TraLai S17 fallback. **F2** Drafter skip thẳng Cấp cuối — workflow tick + Workspace checkbox dynamic confirm. **F3** Approver edit Section 2 (Hạng mục/NCC/Báo giá) khi workflow tick + actor match CurrentLevel + audit ghi PurchaseEvaluationChangelog. Mig 28 `ApprovalWorkflows +6 bool Allow*` (DEFAULT 1 cho AllowReturnToDrafter backward compat, 5 còn lại 0). BE Service `TransitionAsync` extend 3 optional param (returnMode/returnTargetUserId/skipToFinal) + helper `ApplyReturnModeAsync` switch 4 mode. Detail/Quote/Supplier helper `EnsureEditableForDetailsAsync` mới (kế thừa `EnsureDraftAsync` + add ChoDuyet+F3 branch + Admin bypass). FE Admin Designer "Cấu hình nâng cao" section 6 checkbox 3 group. FE eOffice 3 changes mirror 2 app: Trả lại radio picker 1-4 mode + Workspace skip checkbox violet + Section 2 itemsReadOnly approver banner. UAT mode skip dotnet test mỗi chunk (per `feedback_uat_skip_verify`), `npm run build` × 2 app pass mỗi chunk. Stats: **28 mig (+1)** · 59 tables · **~143 endpoints (+1 user-selectable patch existed)** · **34 FE pages (+1 Designer section)** · **84 test pass unchanged** (UAT defer test-after) · **45 gotcha unchanged** · 17 memory · 6 skills · 4 sub-agents seeds-only.**)
+**S21 turn 3:** 2026-05-12 2100 (Session 21 turn 3 — **🎯 Bug fix CRITICAL "Trả về nhưng hệ thống vẫn duyệt" PE workflow (gotcha #45). 2 chunk per-commit `de00887` (BE Chunk A) + `4b29d00` (FE Chunk B) + Chunk C Docs this. Root: PeWorkflowPanel.tsx `isReject` payload (L64-66) thiếu nhánh TraLai → button "← Trả lại" gửi `decision: 1` (Approve) thay vì `2` (Reject) khi target=TraLai(98) → BE ApproveV2Async UPSERT opinion "đã duyệt" + advance Cấp. Inconsistency phụ: dialog `isSendBack` (L247-248) cùng pattern thiếu TraLai → dialog title sai. Fix BE defense-in-depth + FE 3 chỗ × 2 app mirror rule §3.9. Test-before §7 BẮT BUỘC: 3 regression test mới (2 reproduce bug + 1 happy path control) — `dotnet test SolutionErp.slnx` 84 PASS (58 Domain + 26 Infra = +3). `npm run build` × 2 app pass. Stats: 27 mig (no change) · 59 tables · ~142 endpoints · 34 FE pages · **84 test pass (+3)** · **45 gotcha (+1 #45)** · 17 memory entries (no new) · 6 skills. Em main solo (no sub-agent spawn S21 t3 — bug fix reasoning chain cross BE/FE Implementer REFUSE per multi-agent rule).**)
+**S21 turn 2:** 2026-05-12 1800 (Session 21 turn 2 — **🎯 RAG Hybrid setup planning + Cách A validation deep dive. 2 commit (`1f8e9af` plan save 1223 LOC + this chốt). Em main solo (no SOLUTION_ERP sub-agent spawn), delegate claude-code-guide × 2 research Anthropic + community practice. Decision chốt: Cách A defensive (giữ blanket 120K em main + RAG retrieve supplement) over Cách B aggressive (cắt 60-70% blanket). Industry-validated cross 4 Anthropic blog + 5 community tools (Cursor/Continue/Cline/Aider all hybrid). Stack: Voyage-3-large + Qdrant local + FastMCP Python + Streamlit dashboard 7 pages + SQLite event log. Multi-agent cost reality: 4 agents → ~520K cumulative blanket → heavy session ~560K (Cách A) vs ~700K (lazy), saving -20%. 3-layer pattern Phase 1-3 rollout (Layer 1 vector → Layer 2 +BM25 → Layer 3 +reranking, recall ~70% → ~92%). Stats: +1 memory entry (`feedback_rag_hybrid_pattern.md`) +1 plan file (`rag-setup-plan.md` 1500 LOC final). 4 sub-agents vẫn seeds-only. Plan I NEW deferred chờ bro confirm 5 dự án path + stack + Voyage API key + disk cleanup 5-8GB.**)
 **S21 turn 1:** 2026-05-12 0030 (Session 21 turn 1 — **🎯 Add con thứ 4 cicd-monitor (Path A — post-deploy verifier green READ tier). 1 commit `f1c61c9` pushed `36e21c8..f1c61c9 main -> main`, CI skipped per path filter (`**/*.md` paths-ignore docs-only). Trade-off: +~150K spawn extra mỗi run, đổi lại catch deploy ship fail tự động (bundle hash unchanged / mig drift prod / endpoint 500) — recurring blind spot pattern em main solo S20 quên verify ~30% push. Cost reality update: ~750K spawn setup (3 → 4 agents) · ~1.35M heavy session · ~700K optimized cached. Stats: 4 sub-agents seeds-only (+1 cicd-monitor green) · 16 memory entries (no new, update existing `feedback_multi_agent_setup.md` 3 → 4 agents narrative) · 27 mig · 59 tables · ~142 endpoints · 81 test unchanged · 44 gotcha unchanged · 6 skills unchanged. KHÔNG flush 3 agent MEMORY.md (chưa spawn work S21 t1 nên KHÔNG có findings — em main solo via context + Write file).**)
 **S20 wrap:** 2026-05-11 22:00 (Session 20 wrap turns 1-12 — **🎯 14 commit `9dee00d` → `ae1814c`. PE Detail UI restructure 3 yêu cầu (t1-5) + Manual budget drop tên (t6) + Mig 27 admin menu eOffice (t7) + NCC palette 5-màu cycle + Winner icon ✓ đậm + AddSupplier auto-fill master + Responsive laptop nhỏ 4-tầng pattern (t8-11) + Multi-agent infrastructure setup 3 sub-agents (t12). 27 mig (+1) · 59 tables · ~142 endpoints (+1) · 34 FE pages (+1) · 61 menu key (+1) · 81 test pass unchanged · 44 gotcha · 16 memory entries (+2) · 3 sub-agents NEW. Phase 9 UAT iteration mode.**)
 **S20 turn 7:** 2026-05-11 17:00 (Session 20 turn 7 — **🎯 Admin Ẩn/Hiện + Đổi tên menu eOffice (Mig 27). 5 chunk `2ea2d27`→`ef394f8`→`059bfcb`→`1ed6530`→Chunk E Docs. User Q2=b: DisplayLabel CHỈ áp fe-user, admin sidebar giữ Label gốc. Domain MenuItem +IsVisible(true) +DisplayLabel(200). Mig 27 AddVisibilityAndDisplayLabelToMenuItems. BE PATCH /api/menus/{key} [Authorize Policy=Permissions.Update]. NEW FE-admin MenuVisibilityPage ~210 LOC (table inline edit per-row + Save dirty + Khôi phục mặc định + Toggle Eye/EyeOff + 4 StatCard). fe-user Layout filterForUser 2 tầng (USER_HIDDEN_KEYS hardcode + !isVisible dynamic) + effectiveLabel(displayLabel || label) replace 3 callsite. fe-admin Layout KHÔNG đụng. +1 menu key MenuVisibility "Menu eOffice" leaf System Order=94. 27 mig, 59 tables, ~142 endpoints, 34 FE pages, 81 test pass (Q4 UAT defer).**)
 **S20 prev:** 2026-05-11 (Session 20 — **🎯 PE Detail UI restructure 3 yêu cầu user UX. 4 chunk per-commit `9dee00d` → `2bba851` → `f2f01f4` → (current Chunk D Docs).** Q1=a (giữ Section "Chọn NCC TP" riêng), Q2=a "1 hạng mục trước tiên" (NCC shared, demo 1 hạng mục), Q3=a (chỉ hiện NV đã ký), Q4 public luôn (skip dotnet test mỗi chunk theo memory `feedback_uat_skip_verify`, vẫn `npm run build` × 2 app mỗi chunk vì có rename/remove function). **Chunk A (`9dee00d`)**: BE `CreatePurchaseEvaluationCommandHandler` thêm 1 PurchaseEvaluationDetail mặc định khi tạo phiếu — GroupCode="01", GroupName="Hạng mục chính", NoiDung=TenGoiThau, DonGiaNganSach=ThanhTienNganSach=Budget.TongNganSach hoặc BudgetManualAmount fallback 0; Changelog Insert audit. FE reorder PeDetailTabs (mirror 2 app) 1.Thông tin / 2.Hạng mục (lên #2) / 3.Chọn NCC / 4.NCC tham gia / 5.Ý kiến. **Chunk B (`2bba851`)**: ItemsTab restructure thành list `HangMucCard` (1 card / 1 hạng mục, expanded=true mặc định cho 1 hạng mục demo). Header card: GroupCode + NoiDung + 3 stat (KL/ĐG/TT) + NS link Δ nếu có + Pencil/Trash actions + ▼/▶ toggle expand. Expand body: NCC inline table columns NCC / Liên hệ / Điều khoản TT / **File báo giá** / ĐG chưa VAT / ĐG có VAT / Thành tiền / Action. Quote inline click cell → QuoteDialog cũ reuse. Add NCC + Sửa NCC reuse AddSupplierDialog/EditSupplierDialog cũ. Winner ✓ button mỗi NCC row. Drop function `SuppliersTab` (dead code ~134 LOC, replace bằng HangMucCard expand panel). Giữ AddSupplierDialog + EditSupplierDialog + SupplierAttachmentsCell (HangMucCard call lại). Section layout cuối: 1.Thông tin / 2.Hạng mục + Báo giá NCC (nested) / 3.Chọn NCC TP thắng thầu / 4.Ý kiến cấp duyệt — 4 section. **Chunk C (`f2f01f4`)**: Section Ý kiến restructure render layer (KHÔNG đụng Mig 26 schema — vẫn UPSERT 1 row / Level). LevelOpinionsSectionV2 forEach step → 1 `StepOpinionsBox` (replace grid-cols-2 cho N approver). Box header: "Bước N — Tên" + dept badge emerald + "X/Y đã duyệt" counter. Body: filter opinions theo step.order → sort levelOrder asc, signedAt asc → render `StepOpinionEntry` per signed opinion (tên NV + Cấp badge slate + admin override badge amber nếu có + emerald rounded-full timestamp + comment text). NV chưa duyệt KHÔNG hiển thị (Q3=a). Drop function `LevelOpinionBox` (replaced). Mirror fe-admin + fe-user. Verify build pass cả 2 app sau khi catch TS6133 `SuppliersTab` + `SupplierAttachmentsCell` unused (đã giải quyết: drop SuppliersTab, restore SupplierAttachmentsCell vào HangMucCard cột "File báo giá"). 81 test pass (no change — UAT defer)**)
 
-## 📍 Phase hiện tại: **Phase 9 active — UAT V2 testing với user thật** — **59 DB tables (+1 PurchaseEvaluationLevelOpinions Mig 26), 26 migrations (+1 Mig 26), ~141 API endpoints (no new — UPSERT auto qua Service hook không endpoint riêng, Q1=1B), 33 FE pages. 81 unit test pass** (58 Domain + 23 Infra — no change S19, feature UAT defer test theo §7). 44 gotcha. 30 demo user + 1 test user UAT. 6 skill. **5 trạng thái phiếu** (Nháp/Đã gửi duyệt/Trả lại/Từ chối/Đã duyệt). **2 Workflow schemas đồng tồn tại** post-Session 17: (1) Mig 21 `WorkflowDefinition` flat (V1) — pin với PE/Contract cũ + match Dept+PositionLevel. (2) Mig 22-26 `ApprovalWorkflow` (V2) — pin với PE mới + match ApproverUserId 1-1, Steps/Levels group by Order, Bước (Phòng) > Cấp (N NV OR-of-N), Mig 25 +IsUserSelectable admin pin per version, **Mig 26 +PeLevelOpinions sign-off dynamic theo Level**. Service PE branch theo `ApprovalWorkflowId` set or null. Sau UAT chốt → migrate + drop V1 + Contract V2 wire.
+## 📍 Phase hiện tại: **Phase 9 active — UAT V2 testing với user thật** — **59 DB tables (+1 PurchaseEvaluationLevelOpinions Mig 26), 28 migrations (+1 Mig 28 advanced options S21 t4 — 6 bool column trên ApprovalWorkflows), ~143 API endpoints, 34 FE pages. 84 unit test pass** (58 Domain + 26 Infra — baseline +3 PE guard S21 t3, S21 t4 UAT defer test-after per §7). **45 gotcha**. 30 demo user + 1 test user UAT. 6 skill. **5 trạng thái phiếu** (Nháp/Đã gửi duyệt/Trả lại/Từ chối/Đã duyệt). **2 Workflow schemas đồng tồn tại** post-Session 17: (1) Mig 21 `WorkflowDefinition` flat (V1) — pin với PE/Contract cũ + match Dept+PositionLevel. (2) Mig 22-26 `ApprovalWorkflow` (V2) — pin với PE mới + match ApproverUserId 1-1, Steps/Levels group by Order, Bước (Phòng) > Cấp (N NV OR-of-N), Mig 25 +IsUserSelectable admin pin per version, **Mig 26 +PeLevelOpinions sign-off dynamic theo Level**. Service PE branch theo `ApprovalWorkflowId` set or null. Sau UAT chốt → migrate + drop V1 + Contract V2 wire.
 
 ### 🌐 Production URLs
 

docs/changelog/sessions/2026-05-12-2100-s21-turn3-fix-tra-lai-bug45.md

@@ -0,0 +1,182 @@
+# Session 21 turn 3 — 2026-05-12 21:00 — Bug fix CRITICAL "Trả về nhưng hệ thống vẫn duyệt" PE workflow (gotcha #45)
+
+**Dev:** Claude Opus 4.7 1M Max (em main solo, no SOLUTION_ERP sub-agent spawn)
+**Duration:** ~1.5h diagnose + fix + test + docs
+**Base commit:** `0a3b747` (S21 t2 RAG planning chốt)
+**Commits này turn:** `de00887` (BE Chunk A) → `4b29d00` (FE Chunk B) → this (Chunk C Docs)
+
+## Trigger
+
+User UAT 2026-05-12 21:00 screenshot button labeled `← Trả lại` trong PE Workflow Panel (menu "Duyệt") với caption thắc mắc "Trả về nhưng hệ thống vẫn duyệt" + yêu cầu "check lại nhé chỗ Duyệt NCC".
+
+Đây là bug CRITICAL data integrity — NV nhấn "Trả lại" vô tình "duyệt" phiếu sang Cấp tiếp theo + UPSERT opinion vĩnh viễn vào `PurchaseEvaluationLevelOpinions` (Mig 26). Khó rollback vì BE đã `SaveChangesAsync`.
+
+## Diagnose
+
+Em main solo (Implementer REFUSE per multi-agent rule — reasoning chain cross BE/FE+test tightly coupled). Grep `Trả lại|isReject|TraLai` trong fe-user/fe-admin → tìm 3 chỗ inconsistency trong `PeWorkflowPanel.tsx`:
+
+| # | Location | Logic | Bug? |
+|---|---|---|---|
+| 1 | L205-207 button `isSendBack` | include cả `DangSoanThao` lẫn `TraLai` → label `← Trả lại` đúng | ✅ no bug |
+| 2 | L64-66 payload `isReject` | CHỈ check `DangSoanThao`, thiếu `TraLai` → gửi `decision: 1` (Approve) thay vì `2` | 🔴 BUG ROOT |
+| 3 | L247-248 dialog `isSendBack` | CHỈ check `DangSoanThao`, thiếu `TraLai` → title fallback `'✓ Duyệt → Trả lại'` (sai semantic) + no amber warning | 🔴 BUG phụ |
+
+**BE side audit** `PurchaseEvaluationWorkflowService.TransitionAsync`:
+- L51 `if (decision == Reject)` branch → handle BOTH TuChoi (set Phase=TuChoi) + TraLai (set Phase=TraLai, clear pointer). Correct.
+- L97 `APPROVE STEP` branch khi `decision=Approve && fromPhase=ChoDuyet` → `ApproveV2Async` UPSERT opinion + advance Cấp pointer.
+- → Khi FE gửi `decision=1` do bug `isReject` thiếu nhánh TraLai, BE entry → APPROVE branch thay vì REJECT branch → phiếu approve mặc dù user định trả lại.
+
+## Chunk A — BE defense-in-depth + 3 regression test (`de00887`)
+
+### Test-before §7 BẮT BUỘC strict flow
+
+**Step 1:** Write test file `tests/SolutionErp.Infrastructure.Tests/Services/PurchaseEvaluationWorkflowServiceGuardTests.cs` 3 test KHÔNG có BE guard → run → expect FAIL.
+
+**Step 2:** Confirm 2 test FAIL (reproduce bug — BE đi sâu vào ApproveV2Async throw "Phiếu chưa pin workflow definition hoặc workflow không có step") + 1 test PASS (happy path Reject branch — đã pass vì BE đã đúng cho decision=Reject từ Session 17).
+
+**Step 3:** Add BE guard sau L48, trước L51:
+
+```csharp
+// ===== GUARD: targetPhase TraLai/TuChoi BẮT BUỘC decision=Reject =====
+// Defense-in-depth chặn FE inconsistency (gotcha #45 — Session 21 turn 3).
+// Bug: button "← Trả lại" gửi decision=Approve khi target=TraLai → BE skip
+// Reject branch → enter APPROVE STEP → ApproveV2Async UPSERT opinion.
+if ((targetPhase == PurchaseEvaluationPhase.TraLai
+        || targetPhase == PurchaseEvaluationPhase.TuChoi)
+    && decision != ApprovalDecision.Reject)
+{
+    throw new ConflictException(
+        $"Transition tới {targetPhase} BẮT BUỘC decision=Reject (nhận {decision}). " +
+        "Báo lỗi caller — payload mismatch giữa target phase và decision " +
+        "(xem gotcha #45 + docs/workflow-contract.md).");
+}
+```
+
+**Step 4:** Re-run test → 3/3 PASS. Run full suite → 84/84 PASS (58 Domain + 26 Infra = +3 from 81 baseline).
+
+### 3 test cases
+
+1. **`TransitionAsync_TargetTraLai_WithApproveDecision_Throws_AndDoesNotMutateState`** — Bug reproduce. Setup PE ở Phase=ChoDuyet, CurrentApprovalLevelOrder=1. Act: gửi target=TraLai + decision=Approve. Assert: throw `ConflictException` "*TraLai*Reject*" + Phase KHÔNG đổi + CurrentApprovalLevelOrder=1 (no advance).
+2. **`TransitionAsync_TargetTuChoi_WithApproveDecision_Throws_AndDoesNotMutateState`** — Consistency cover. Cùng pattern với TuChoi.
+3. **`TransitionAsync_TargetTraLai_WithRejectDecision_SetsPhaseTraLai`** — Happy path control. decision=Reject + target=TraLai → BE đi vào Reject branch, set Phase=TraLai, clear pointer (CurrentApprovalLevelOrder=null + CurrentWorkflowStepIndex=null + SlaDeadline=null).
+
++ `NoOpNotificationService internal sealed` stub trong cùng file (Tests scope) — reusable cho future PE service tests, avoid `INotificationService` real DI complexity.
+
+### Pattern reusable
+- **Boundary guard semantic invariant.** Bất kỳ BE service nào nhận payload từ FE → audit invariant `(domain state X) ⇔ (input parameter Y)` → throw early nếu mismatch. Defense-in-depth thay vì trust FE đúng.
+- **Test-before flow strict:** Write test → confirm FAIL với exception KHÁC expected (proves bug reproduce) → add fix → confirm PASS với exception ĐÚNG expected. KHÔNG bỏ qua bước "confirm FAIL" — đảm bảo test actually catches bug.
+
+## Chunk B — FE fix mirror 2 app (`4b29d00`)
+
+3 chỗ × 2 app = 6 edits.
+
+### fe-user/src/components/pe/PeWorkflowPanel.tsx
+
+**Edit #1 (L64-66 `isReject`):**
+
+```typescript
+const isReject = target === PurchaseEvaluationPhase.TuChoi
+  || (target === PurchaseEvaluationPhase.DangSoanThao
+      && evaluation.phase !== PurchaseEvaluationPhase.DangSoanThao)
+  || (target === PurchaseEvaluationPhase.TraLai             // ← THÊM nhánh TraLai
+      && evaluation.phase !== PurchaseEvaluationPhase.TraLai)
+```
+
+**Edit #2 (L247-248 dialog `isSendBack`):**
+
+```typescript
+const isSendBack = (target === PurchaseEvaluationPhase.DangSoanThao
+                    || target === PurchaseEvaluationPhase.TraLai)   // ← THÊM TraLai
+  && evaluation.phase !== PurchaseEvaluationPhase.DangSoanThao
+  && evaluation.phase !== PurchaseEvaluationPhase.TraLai             // ← THÊM guard
+```
+
+**Comment update:** Thêm context bug + cross-ref BE guard Chunk A trong comment.
+
+### fe-admin/src/components/pe/PeWorkflowPanel.tsx
+
+Mirror y hệt (rule §3.9 mirror 2 app — duplicate có chủ đích).
+
+### Verify
+
+```bash
+# fe-user
+cd fe-user && npm run build
+✓ built in 17.91s
+
+# fe-admin  
+cd fe-admin && npm run build
+✓ built in 6.71s
+```
+
+0 TS6 err, 0 new warnings. Warning chunk size pre-existing (KHÔNG introduced).
+
+## Chunk C — Docs (this commit)
+
+### `docs/gotchas.md` +#45
+
+~120 dòng narrative đầy đủ KEEP rule §6.5:
+- **Triệu chứng** — UAT screenshot user mô tả hành vi
+- **Root cause** — 3 chỗ inconsistency table + BE service path narrative
+- **Severity** CRITICAL — data integrity issue khó rollback
+- **Fix Chunk A** BE code block + 3 test list
+- **Fix Chunk B** FE code block diff
+- **Pattern reusable** — boundary guard semantic invariant + button label ↔ payload sync
+- **Phòng tránh tương lai** — grep audit khi spec mới thêm phase + test-before §7 strict flow
+- **References** — 2 commit + Session 17 spec
+
+`docs/gotchas.md` checklist debug +entry 22 quick lookup.
+
+### `docs/STATUS.md`
+
+Edit Last updated header thêm S21 t3 + count 81→84 test + 44→45 gotcha. Giữ nguyên S21 t2/t1/S20 narrative cũ (rule §6.5 KEEP).
+
+### `docs/HANDOFF.md`
+
+Insert TL;DR S21 t3 section trên cùng (trước S21 t2). Header Last updated mới + narrative đầy đủ Chunk A/B/C + state table cumulative. Giữ S21 t2/t1/S20 narrative cũ.
+
+### Session log
+
+File này — `docs/changelog/sessions/2026-05-12-2100-s21-turn3-fix-tra-lai-bug45.md`.
+
+## Stats cumulative
+
+| Metric | Trước (S21 t2) | Sau (S21 t3) | Δ |
+|---|---|---|---|
+| DB tables | 59 | 59 | 0 |
+| Migrations | 27 | 27 | 0 |
+| Endpoints | ~142 | ~142 | 0 |
+| FE pages | 34 | 34 | 0 |
+| **Unit tests** | 81 | **84** | **+3** (PE guard) |
+| **Gotchas** | 44 | **45** | **+1** (#45) |
+| Memory entries | 17 | 17 | 0 |
+| Skills | 6 | 6 | 0 |
+| Sub-agents | 4 seeds-only | 4 seeds-only | 0 |
+| Commits S21 t3 | — | **3** | (`de00887` + `4b29d00` + this) |
+
+## Lessons learned
+
+1. **Mảng inconsistency 3 chỗ cùng pattern** — khi spec mới thêm value vào set check (vd Session 17 thêm `TraLai` làm Phase RIÊNG thay vì DangSoanThao revert), DỄ QUÊN grep TOÀN BỘ logic check `=== OldValue` để thêm `|| === NewValue`. Tốt nhất extract helper function `isReject(target, currentPhase): boolean` share 1 nơi thay vì duplicate 3 chỗ.
+2. **BE guard defense-in-depth có giá trị thực** — trong S21 t3, nếu BE chỉ trust FE đúng → bug ship prod, user UAT report, mất data integrity. BE guard early catch payload mismatch + ConflictException rõ ràng → fix nhanh + safe.
+3. **Test-before flow strict không chỉ là "viết test" — còn confirm FAIL** — em main đầu tiên định viết test + fix cùng commit (cho gọn). Nhưng test-before §7 BẮT BUỘC confirm test FAIL trước fix. Bước này quan trọng — confirm test actually reproduce bug (assert đúng exception type/message), không chỉ là "test xanh sau fix".
+4. **Multi-agent decision tree áp đúng** — Bug fix tightly coupled BE+FE+test reasoning chain → Implementer REFUSE per rule (Cognition "writes single-threaded"). Em main solo correct decision, KHÔNG cố split → tránh agent thrash.
+
+## Handoff
+
+- ✅ Chunk A `de00887` committed local — chưa push
+- ✅ Chunk B `4b29d00` committed local — chưa push
+- ✅ Chunk C (this) — committed sau khi save session log
+- ⏭ **PENDING bro confirm push remote** — `git push origin main` 3 commit ahead `0a3b747..HEAD`
+- ⏭ Sau push: CI sẽ trigger (NOT docs-only — có file `.cs` + `.tsx`) → 🟩 CICD Monitor spawn smoke verify (per plan G Trial Week 1)
+
+User next action expected: "fix đi rồi tao giao thêm task" → sau Chunk C wrap → bro chốt task tiếp theo (có thể là Plan B Contract V2 wire hoặc fix khác phát sinh UAT).
+
+## References
+
+- Gotcha #45: `docs/gotchas.md`
+- BE service: `src/Backend/SolutionErp.Infrastructure/Services/PurchaseEvaluationWorkflowService.cs`
+- FE component (× 2 app): `{fe-admin,fe-user}/src/components/pe/PeWorkflowPanel.tsx`
+- Test: `tests/SolutionErp.Infrastructure.Tests/Services/PurchaseEvaluationWorkflowServiceGuardTests.cs`
+- Workflow spec Session 17: `PurchaseEvaluationPhase.cs` enum doc + Service comment L15-19
+- Rule §7 test-before: `docs/rules.md`
+- Rule §3.9 mirror 2 FE: `docs/rules.md`

docs/changelog/sessions/2026-05-13-1200-s21-turn4-pe-workflow-advanced-options.md

@@ -0,0 +1,316 @@
+# Session 21 turn 4 — 2026-05-13 12:00 — PE Workflow advanced options (F1+F2+F3, Mig 28)
+
+**Dev:** Claude Opus 4.7 1M Max (em main solo — 3 feature multi-layer Implementer REFUSE per cross-stack reasoning chain rule)
+**Duration:** ~3h (clarify Q&A 2 lượt + 5 chunk implement + verify build cả 2 app mỗi chunk)
+**Base commit:** `6d30ba4` (S21 t3 fix gotcha #45 Chunk C Docs)
+**Commits này turn:** `0294693` (A schema) → `c56024b` (B BE) → `a508564` (C FE Admin) → `d27caaf` (D FE eOffice) → this (E Docs)
+
+## Trigger
+
+User chốt 3 tính năng mới trong "Quy trình duyệt NCC":
+
+1. **F1** — 4 mode Trả lại trong workflow (admin stick per workflow):
+   - Cho trả về 1 bậc trước đó
+   - Cho trả về người chỉ định
+   - Trả về người soạn thảo
+   - Workflow tick stick mode nào enabled → user eOffice dropdown chỉ hiện mode đó
+
+2. **F2** — Drafter chọn "Gửi duyệt thẳng cấp" (vd skip → CEO):
+   - "Các bước này đều ghi nhận vào quy trình duyệt phiếu"
+
+3. **F3** — Approver chỉnh sửa phiếu (Section 2 chi tiết):
+   - "lưu vào lịch sử chỉnh sửa luôn"
+
+## Clarify Q&A (2 lượt AskUserQuestion)
+
+### Lượt 1 — Schema + UX scope:
+
+| Câu | User chốt |
+|---|---|
+| F1 "Trả về 1 bậc trước đó" nghĩa là gì? | **Cả 2 mode (admin chọn)** — 1 Cấp + 1 Bước stick độc lập |
+| F1 "Người chỉ định" nguồn từ đâu? | **Approver pick runtime** — dropdown từ list NV đã ký (PeLevelOpinions) |
+| F2 skip scope | **Chỉ skip tới Level cuối (CEO)** — Dropdown 2 option |
+| F3 edit scope | **Section 2 (Hạng mục + NCC + Báo giá)** — KHÔNG đụng Header, KHÔNG reset workflow |
+
+### Lượt 2 — Behavior + admin enable:
+
+| Câu | User chốt |
+|---|---|
+| 3 mode Trả lại behavior | **Giữ ChoDuyet, lùi pointer** (peer review chain). Mode Drafter giữ Phase=TraLai S17 |
+| F2+F3 admin enable | **Cả 2 cần admin tick** per workflow (audit nghiêm) |
+| F3 approver perm | **Mọi approver Cấp đang active** (currentLevel match) |
+| Test timing | **Test-after UAT default Phase 9** (skip dotnet test mỗi chunk, npm build × 2 app) |
+
+## Chunk A — Schema + Migration 28 (`0294693`)
+
+### Domain `ApprovalWorkflow.cs` +6 bool
+
+```csharp
+public bool AllowReturnOneLevel { get; set; }        // F1 mode 1
+public bool AllowReturnOneStep { get; set; }         // F1 mode 2
+public bool AllowReturnToAssignee { get; set; }      // F1 mode 3
+public bool AllowReturnToDrafter { get; set; } = true;  // F1 mode 4 (backward compat S17)
+public bool AllowDrafterSkipToFinal { get; set; }    // F2
+public bool AllowApproverEditDetails { get; set; }   // F3
+```
+
+### EF config `ApprovalWorkflowConfiguration`
+
+```csharp
+e.Property(x => x.AllowReturnOneLevel).HasDefaultValue(false);
+// ... 4 more false ...
+e.Property(x => x.AllowReturnToDrafter).HasDefaultValue(true);  // backfill rows cũ
+```
+
+### Migration 28 `AddAdvancedOptionsToApprovalWorkflows`
+
+- 6 AddColumn bit NOT NULL DEFAULT 0/1
+- 3-file rule complete (mig.cs + Designer.cs + Snapshot.cs)
+- Apply LocalDB Dev + Design success
+
+## Chunk B — BE Service + handlers + DTOs (`c56024b`)
+
+### Service signature extend (backward compat)
+
+```csharp
+public async Task TransitionAsync(
+    PurchaseEvaluation evaluation,
+    PurchaseEvaluationPhase targetPhase,
+    Guid? actorUserId,
+    IReadOnlyList<string> actorRoles,
+    ApprovalDecision decision,
+    string? comment,
+    WorkflowReturnMode? returnMode = null,        // ← NEW
+    Guid? returnTargetUserId = null,              // ← NEW
+    bool skipToFinal = false,                     // ← NEW
+    CancellationToken ct = default)
+```
+
+`WorkflowReturnMode` enum: OneLevel=1, OneStep=2, Assignee=3, Drafter=4.
+
+### REJECT branch extend với `ApplyReturnModeAsync`
+
+```csharp
+// Inside REJECT branch (line 51+)
+var effectiveMode = returnMode ?? WorkflowReturnMode.Drafter;
+var returnSummary = await ApplyReturnModeAsync(
+    evaluation, effectiveMode, returnTargetUserId, isAdmin, ct);
+comment = $"{comment} [{returnSummary}]";
+```
+
+Helper `ApplyReturnModeAsync` switch 4 mode:
+
+```csharp
+// OneLevel — lùi 1 Cấp trong cùng Step. Bước 1 Cấp 1 → fallback Drafter.
+if (curLevel > 1) {
+    evaluation.CurrentApprovalLevelOrder = curLevel - 1;
+    summary = $"Trả về Cấp {curLevel - 1}";
+}
+else if (curStepIdx > 0) {
+    var prevStep = stepsOrdered[curStepIdx - 1];
+    evaluation.CurrentWorkflowStepIndex = curStepIdx - 1;
+    evaluation.CurrentApprovalLevelOrder = prevStep.Levels.Max(l => l.Order);
+    summary = $"Trả về Bước {prevStep.Order} Cấp {maxLevel} (Bước trước)";
+}
+else { /* fallback Drafter */ }
+
+// OneStep — lùi sang Bước trước, set Level = max của Bước đó. Bước 1 → fallback.
+// Assignee — tìm Step+Level match returnTargetUserId trong workflow.
+// Drafter — Phase=TraLai clear pointer (S17 backward compat).
+```
+
+3 mode đầu giữ Phase=ChoDuyet + reset SLA 7d. Admin bypass workflow.Allow* flag check.
+
+### DRAFTER trình branch extend với F2
+
+```csharp
+if (skipToFinal && evaluation.ApprovalWorkflowId is Guid skipAwId) {
+    // Workflow.AllowDrafterSkipToFinal required (non-admin)
+    if (!wfSkip.AllowDrafterSkipToFinal)
+        throw new ConflictException("Workflow không bật mode 'Gửi thẳng Cấp cuối'.");
+    evaluation.CurrentWorkflowStepIndex = wfSkip.Steps.Count - 1;  // 0-based last
+    evaluation.CurrentApprovalLevelOrder = finalStep.Levels.Max(l => l.Order);
+    comment = $"{comment} [Drafter gửi thẳng Cấp cuối — skip Bước/Cấp trung gian]";
+}
+```
+
+### Helper edit guard `EnsureEditableForDetailsAsync` (PurchaseEvaluationDraftGuard class)
+
+```csharp
+public static async Task<PurchaseEvaluation> EnsureEditableForDetailsAsync(
+    IApplicationDbContext db, Guid id, ICurrentUser currentUser, CancellationToken ct)
+{
+    var pe = await db.PurchaseEvaluations.FirstOrDefaultAsync(...);
+
+    // Drafter scope — bypass current Controller [Authorize] handles role
+    if (pe.Phase == DangSoanThao || pe.Phase == TraLai) return pe;
+
+    // F3 Approver scope (Mig 28) — chỉ ChoDuyet
+    if (pe.Phase == ChoDuyet && currentUser.UserId is Guid actorUserId) {
+        if (currentUser.Roles.Contains(Admin)) return pe;  // bypass
+
+        var workflow = await db.ApprovalWorkflows.Include(w => w.Steps)...
+        if (!workflow.AllowApproverEditDetails)
+            throw new ConflictException("Workflow không bật mode...");
+
+        var level = step.Levels.FirstOrDefault(lv => lv.Order == levelOrder);
+        if (level.ApproverUserId != actorUserId)
+            throw new ForbiddenException("Chỉ NV phụ trách Bước X / Cấp Y...");
+
+        return pe;
+    }
+
+    throw new ConflictException($"Phiếu PE ở Phase={pe.Phase}, không thể chỉnh sửa.");
+}
+```
+
+### 8 handler switch + audit changelog
+
+- `PurchaseEvaluationDetailFeatures.cs`: Add/Update/Delete + Quote Upsert/Delete (5)
+- `PurchaseEvaluationSupplierFeatures.cs`: Add/Update/Remove (3) — **bonus security fix**: trước đây Supplier handlers HOÀN TOÀN KHÔNG có phase guard!
+
+Update/Delete handlers trước đây silent → thêm changelog `PhaseAtChange + UserId + Summary` (append `[Approver edit khi đang duyệt]` khi phase=ChoDuyet).
+
+### Command DTO + DTOs extend
+
+- `TransitionPurchaseEvaluationCommand` +3 optional field + Validator
+- `ApprovalWorkflowOptionsDto` NEW sub-record (6 Allow* flag)
+- `PurchaseEvaluationDetailBundleDto` +WorkflowOptions field (null nếu V1 legacy)
+- `AwDefinitionDto` +6 Allow* (admin Designer GET)
+- `CreateAwDefinitionCommand` +6 Allow* param (admin Designer POST)
+
+### Verify
+- `dotnet build SolutionErp.slnx` → 0 err, 2 warn pre-existing DocxRenderer
+- 3 regression test gotcha #45 vẫn PASS (signature backward compat)
+
+## Chunk C — FE Admin Designer (`a508564`)
+
+### `ApprovalWorkflowsV2Page.tsx` Section "Cấu hình nâng cao" 6 checkbox
+
+Container amber-50/30 + border distinct với Steps. 3 sub-group:
+
+1. **Mode Trả lại** (4 checkbox):
+   - ☐ Trả về 1 Cấp trước (peer review chain trong cùng Bước)
+   - ☐ Trả về 1 Bước trước (Cấp cuối Bước trước nhận lại)
+   - ☐ Trả về Người chỉ định (pick runtime từ NV đã ký)
+   - ☑ Trả về Người soạn thảo (default checked = backward compat S17)
+
+2. **Drafter gửi duyệt** (1 checkbox):
+   - ☐ Cho phép Drafter gửi thẳng Cấp cuối
+
+3. **Approver chỉnh sửa phiếu** (1 checkbox):
+   - ☐ Cho phép Approver chỉnh sửa Section 2 (Hạng mục + NCC + Báo giá)
+
+DTO types + state defaults từ cloneFrom (giữ config version trước) hoặc S17 fallback. POST body propagate.
+
+fe-user KHÔNG mirror (Designer admin-only).
+
+## Chunk D — FE eOffice (`d27caaf`) mirror 2 app
+
+### Types `purchaseEvaluation.ts`
+
+```typescript
+export type ApprovalWorkflowOptions = {
+  allowReturnOneLevel: boolean
+  // ... 5 more
+}
+
+export const WorkflowReturnMode = {
+  OneLevel: 1, OneStep: 2, Assignee: 3, Drafter: 4,
+} as const
+
+export type PeDetailBundle = {
+  // ...
+  workflowOptions: ApprovalWorkflowOptions | null
+}
+```
+
+### `PeWorkflowPanel.tsx` F1 Trả lại radio picker
+
+State `returnMode` + `returnTargetUserId`. Dialog render 1-4 radio mode enabled theo `wfOptions.Allow*`. Assignee mode → submodal Select pick từ `evaluation.levelOpinions` (NV đã ký, dedupe by userId).
+
+Banner amber rounded dưới mô tả hành vi mode chọn:
+- Drafter: "Phiếu sẽ về 'Trả lại'. Drafter có thể sửa rồi trình lại từ Cấp 1 Bước 1."
+- Assignee: "Phiếu sẽ về Cấp/Bước của NV đã chọn..."
+- OneLevel/OneStep: "Phiếu sẽ lùi pointer (vẫn 'Đã gửi duyệt')..."
+
+Mutation payload +`returnMode` +`returnTargetUserId` khi `isTraLaiAction`.
+
+### `PeDetailTabs.tsx` F2 Drafter skip
+
+State `skipToFinal` + `allowSkipToFinal` từ workflowOptions. submitForApproval mutationFn accept `opts.skipToFinal`. Workspace action bar: checkbox violet conditional. Confirm dialog message + button label dynamic.
+
+### `PeDetailTabs.tsx` F3 Approver edit Section 2
+
+useAuth import + compute `approverEditMode`:
+
+```typescript
+const approverEditMode = evaluation.phase === ChoDuyet
+  && (evaluation.workflowOptions?.allowApproverEditDetails ?? false)
+  && actorMatchesLevel  // isAdmin || actor.id in currentApproval.approvers
+const itemsReadOnly = readOnly && !approverEditMode
+```
+
+Banner violet "ⓘ Bạn được phép chỉnh sửa..." khi approverEditMode + readOnly (Duyệt menu).
+
+InfoTab / NccSelectorRow / BudgetFieldRow GIỮ strict isEditablePhase (Header + Section 3 KHÔNG trong F3 scope).
+
+### Verify
+- `npm run build × 2 app` pass (fe-user 7.52s + fe-admin 499ms cached)
+- 0 TS6 err, warning chunk size pre-existing
+
+## Chunk E — Docs (this commit)
+
+- `docs/database/schema-diagram.md §14` title "Mig 22-28, S17-21" + thêm 6 column Allow* trong Core block với inline comment F1/F2/F3
+- `docs/STATUS.md` Last updated S21 t4 + count 27→28 mig + UAT defer test count unchanged
+- `docs/HANDOFF.md` TL;DR S21 t4 đầy đủ (5 chunk narrative + Q&A + pattern reusable)
+- Session log file này
+
+## Stats cumulative S21 t4
+
+| Metric | Trước (S21 t3) | Sau (S21 t4) | Δ |
+|---|---|---|---|
+| DB tables | 59 | 59 | 0 |
+| **Migrations** | 27 | **28** | **+1** (Mig 28) |
+| Endpoints | ~142 | ~143 | +1 (transitions body extend) |
+| FE pages | 34 | 34 | 0 (Designer extend) |
+| **Unit tests** | 84 | **84** | 0 (UAT defer test-after §7) |
+| Gotchas | 45 | 45 | 0 |
+| Memory entries | 17 | 17 | 0 |
+| Skills | 6 | 6 | 0 |
+| Sub-agents | 4 seeds-only | 4 seeds-only | 0 |
+| Commits S21 t4 | — | **5** | `0294693` → `c56024b` → `a508564` → `d27caaf` → this |
+
+## Lessons learned
+
+1. **Backward-compat option pattern.** Thêm 6 cột mới với 1 cột default TRUE (AllowReturnToDrafter S17 fallback) + 5 cột default FALSE (admin opt-in) → workflow cũ chạy đúng sau deploy, không breaking change. Pattern reusable cho future feature flags.
+
+2. **Boundary helper pattern** (extension thay vì rewrite). Helper cũ `EnsureDraftAsync` strict DangSoanThao only → thêm helper mới `EnsureEditableForDetailsAsync` accept thêm Approver scope. KHÔNG rename + KHÔNG break cũ → coexistence safe. 8 handler switch cleanly.
+
+3. **Multi-agent decision tree áp đúng**. 3 feature multi-layer (Domain + Mig + Service + 8 handler + 2 FE app + 4 DTO file) — tightly coupled reasoning chain → Implementer REFUSE per Cognition "writes single-threaded". Em main solo decision đúng, KHÔNG split tránh agent thrash.
+
+4. **Per-chunk discipline (5 chunk A-E)** mặc dù big-feature multi-layer >1000 LOC. Mỗi chunk verify build pass trước commit → rollback dễ nếu fail. Audit trail commit history rõ ràng cho future debug.
+
+5. **Test-after UAT default Phase 9** chấp nhận được khi feature nhánh enable mới (admin opt-in). Test-before BẮT BUỘC chỉ cho bug fix (gotcha #45 S21 t3 đã làm). Cảnh báo carry: Plan C test-after candidate cumulative ngày càng nhiều — cần dedicated commit "Test catch-up S21 t1-t4" sau UAT ổn.
+
+## Handoff
+
+- ✅ Chunk A `0294693` BE schema + Mig 28 committed local
+- ✅ Chunk B `c56024b` BE Service + handlers + DTOs committed local
+- ✅ Chunk C `a508564` FE Admin Designer committed local
+- ✅ Chunk D `d27caaf` FE eOffice mirror 2 app committed local
+- ✅ Chunk E (this) — Docs commit sau khi save session log
+- ⏭ **PENDING bro confirm push remote** — `git push origin main` 8 commit ahead `0a3b747..HEAD` (S21 t3 fix gotcha #45 + S21 t4 F1+F2+F3)
+
+User next action expected: UAT test 3 feature mới trong env Prod hoặc local. Sau UAT 2-3 lần ổn → Plan C bundle test-after catch up.
+
+## References
+
+- BE Service: `src/Backend/SolutionErp.Infrastructure/Services/PurchaseEvaluationWorkflowService.cs`
+- BE entity: `src/Backend/SolutionErp.Domain/ApprovalWorkflowsV2/ApprovalWorkflow.cs`
+- BE handlers: `src/Backend/SolutionErp.Application/PurchaseEvaluations/{PurchaseEvaluationFeatures, PurchaseEvaluationDetailFeatures, PurchaseEvaluationSupplierFeatures}.cs`
+- Mig 28: `src/Backend/SolutionErp.Infrastructure/Persistence/Migrations/20260513114505_AddAdvancedOptionsToApprovalWorkflows.cs`
+- FE Admin Designer: `fe-admin/src/pages/system/ApprovalWorkflowsV2Page.tsx`
+- FE eOffice × 2 app: `{fe-admin,fe-user}/src/components/pe/PeWorkflowPanel.tsx` + `PeDetailTabs.tsx` + `types/purchaseEvaluation.ts`
+- Spec context: gotcha #45 S21 t3 BE guard payload mismatch + Session 17 spec 5 trạng thái
+- Rules: §3.9 mirror 2 FE, §6.5 KEEP narrative, §7 test timing, `feedback_uat_skip_verify`, `feedback_per_chunk_commit`

docs/database/schema-diagram.md

@@ -715,7 +715,7 @@ CREATE TABLE PurchaseEvaluationDepartmentOpinions (
 CREATE UNIQUE INDEX IX_PEDeptOpinions_PEId_Kind ON PurchaseEvaluationDepartmentOpinions (PurchaseEvaluationId, Kind);
 ```
 
-## 14. ApprovalWorkflow V2 schema (Migration 22-25, Session 17-18 — 3 bảng mới + 3 column)
+## 14. ApprovalWorkflow V2 schema (Migration 22-28, Session 17-21 — 3 bảng mới + 9 column)
 
 Schema riêng song song WorkflowDefinition V1 (Mig 21) — pin per phiếu PE.
 V1 vẫn giữ cho phiếu cũ; V2 mới là active cho phiếu tạo từ Session 17 trở đi.
@@ -728,6 +728,15 @@ ApprovalWorkflows
 ├── ApplicableType (1=DuyetNcc, 2=DuyetNccPhuongAn, 3=Contract)
 ├── Name, Description, IsActive, ActivatedAt
 ├── IsUserSelectable (Mig 25, S18) — admin pin/unpin cho user pick lúc create phiếu
+│
+├── Mig 28 (S21 t4) — 6 advanced options "Cấu hình nâng cao" per workflow:
+├── AllowReturnOneLevel       bit DEFAULT 0  — F1 mode: Trả về 1 Cấp trước (peer review)
+├── AllowReturnOneStep        bit DEFAULT 0  — F1 mode: Trả về 1 Bước trước
+├── AllowReturnToAssignee     bit DEFAULT 0  — F1 mode: Trả về Người chỉ định (pick runtime)
+├── AllowReturnToDrafter      bit DEFAULT 1  — F1 mode: Trả về Drafter (S17 backward compat)
+├── AllowDrafterSkipToFinal   bit DEFAULT 0  — F2: Drafter trình thẳng Cấp cuối, skip trung gian
+├── AllowApproverEditDetails  bit DEFAULT 0  — F3: Approver chỉnh Section 2 lúc đang duyệt
+│
 └── (audit) CreatedAt, UpdatedAt, CreatedBy, UpdatedBy
 
 ApprovalWorkflowSteps  (FK Cascade ApprovalWorkflowId, FK Restrict DepartmentId)

docs/gotchas.md

@@ -637,6 +637,76 @@ public class ApprovalWorkflowsV2Controller(IMediator mediator) : ControllerBase
 
 **FE diagnostic improvement:** TanStack Query error nên hiển thị warning UI (toast hoặc banner) thay vì silent. Hiện tại `useQuery` catch silent → debug khó. Future: wire `onError` handler global show generic error toast.
 
+### 45. PE "Trả về nhưng hệ thống vẫn duyệt" — FE button label vs decision payload mismatch (Session 21 turn 3)
+
+**Triệu chứng:** UAT 2026-05-12 — User bro screenshot button labeled `← Trả lại` trong PE Workflow Panel (menu "Duyệt"), nhấn vào nhưng phiếu KHÔNG về phase TraLai — ngược lại tiến qua Cấp tiếp theo (hệ thống ghi nhận approve). User mô tả hành vi: "Trả về nhưng hệ thống vẫn duyệt".
+
+**Root cause:** `PeWorkflowPanel.tsx` có 3 chỗ check transition type với logic KHÔNG sync giữa nhau:
+
+- **L205-207** `isSendBack` (button label color): include cả `DangSoanThao` lẫn `TraLai` từ phase trung gian → label hiển thị `← Trả lại` đúng.
+- **L64-66** `isReject` (payload `decision` gửi BE): CHỈ check `DangSoanThao`, **thiếu `TraLai`** → khi target=TraLai (98), `isReject=false` → payload `decision: 1` (Approve) thay vì `2` (Reject).
+- **L247-248** dialog `isSendBack` (title + warning): CHỈ check `DangSoanThao`, **thiếu `TraLai`** → dialog title fallback `'✓ Duyệt → Trả lại'` (sai semantic) + KHÔNG hiển thị amber warning "Phiếu sẽ về Đang soạn thảo".
+
+BE `PurchaseEvaluationWorkflowService.TransitionAsync`:
+- L51 `if (decision == Reject)` branch → set Phase=TraLai correctly khi decision=Reject.
+- L97 `APPROVE STEP` branch khi decision=Approve + fromPhase=ChoDuyet → `ApproveV2Async` UPSERT opinion = "đã duyệt" + advance Cấp.
+- → Khi FE gửi `decision=1` (do bug `isReject`), BE đi vào nhánh APPROVE thay vì REJECT → phiếu được ghi nhận approve dù user định trả lại.
+
+**Severity:** 🔴 CRITICAL — data integrity issue. NV nhấn "Trả lại" sẽ vô tình "duyệt" phiếu sang Cấp tiếp theo + UPSERT opinion vĩnh viễn vào `PurchaseEvaluationLevelOpinions` (Mig 26). Khó rollback vì BE đã `SaveChangesAsync`.
+
+**Fix Chunk A (`de00887` BE defense-in-depth):**
+```csharp
+// PurchaseEvaluationWorkflowService.cs sau set isAdmin/isSystem (L48), trước REJECT branch (L51)
+if ((targetPhase == PurchaseEvaluationPhase.TraLai
+        || targetPhase == PurchaseEvaluationPhase.TuChoi)
+    && decision != ApprovalDecision.Reject)
+{
+    throw new ConflictException(
+        $"Transition tới {targetPhase} BẮT BUỘC decision=Reject (nhận {decision}). " +
+        "Báo lỗi caller — payload mismatch giữa target phase và decision.");
+}
+```
+
+Boundary protection cho mọi caller tương lai (API client / mobile / cron retry). 3 regression test:
+- `TransitionAsync_TargetTraLai_WithApproveDecision_Throws_AndDoesNotMutateState` (bug reproduce)
+- `TransitionAsync_TargetTuChoi_WithApproveDecision_Throws_AndDoesNotMutateState` (consistency cover)
+- `TransitionAsync_TargetTraLai_WithRejectDecision_SetsPhaseTraLai` (happy path control)
+
+**Fix Chunk B (`4b29d00` FE mirror 2 app):**
+```typescript
+// PeWorkflowPanel.tsx (fe-user + fe-admin) — 3 chỗ × 2 app
+
+// Chỗ 1: isReject payload (line 64-66)
+const isReject = target === PurchaseEvaluationPhase.TuChoi
+  || (target === PurchaseEvaluationPhase.DangSoanThao
+      && evaluation.phase !== PurchaseEvaluationPhase.DangSoanThao)
+  || (target === PurchaseEvaluationPhase.TraLai             // ← THÊM
+      && evaluation.phase !== PurchaseEvaluationPhase.TraLai)
+
+// Chỗ 2: dialog isSendBack (line 247-248)
+const isSendBack = (target === PurchaseEvaluationPhase.DangSoanThao
+                    || target === PurchaseEvaluationPhase.TraLai)   // ← THÊM
+  && evaluation.phase !== PurchaseEvaluationPhase.DangSoanThao
+  && evaluation.phase !== PurchaseEvaluationPhase.TraLai             // ← THÊM
+```
+
+Chỗ 3 (button label `isSendBack` L205-207) đã đúng từ S17, KHÔNG đụng.
+
+**Pattern reusable — invariant check khi viết FE workflow transition:**
+1. Button label condition (visual) phải SYNC với payload decision (semantic).
+2. Dialog title/warning condition phải SYNC với button label + payload.
+3. Tốt nhất: extract `isReject(target, currentPhase)` thành 1 helper FE + BE share semantic — KHÔNG duplicate logic giữa 3 chỗ.
+
+**Phòng tránh tương lai:**
+- Khi spec mới có thêm phase terminal/intermediate (vd Session 17 thêm TraLai làm Phase RIÊNG thay vì DangSoanThao revert), audit grep TOÀN BỘ logic check `=== DangSoanThao` để xem chỗ nào cần thêm `|| === NewPhase`.
+- BE guard early invariant `(targetPhase ∈ terminalSet) ⇔ (decision == Reject)` thay vì trust FE payload.
+- Test-before bug fix BẮT BUỘC §7 — 3 test cover bug reproduce + consistency + happy path.
+
+**References:**
+- Commit fix: `de00887` (BE Chunk A) + `4b29d00` (FE Chunk B)
+- Spec Session 17: `feedback_n_stage_workflow_pattern` DEPRECATED + spec mới trong `PurchaseEvaluationWorkflowService.cs` comment L15-19
+- State machine 5 trạng thái: Nháp / Đã gửi duyệt / **Trả lại (98) — Phase RIÊNG** / Từ chối / Đã duyệt
+
 ## Checklist debug bug mới
 
 1. Build pass không? → fail → check using + package version compat
@@ -660,3 +730,4 @@ public class ApprovalWorkflowsV2Controller(IMediator mediator) : ControllerBase
 19. Nếu npm install caching fail `tsc not found` → KHÔNG dùng junction Move-Item, thử robocopy/Copy-Item (#40)
 20. Nếu CI vẫn trigger khi commit MD-only → paths-ignore trong on:push không match patterns đúng (#41)
 21. Nếu user phàn nàn "feature work cho admin nhưng user empty/403 silent" → check class-level Authorize policy có over-restrict cho non-admin không, split per action (#44)
+22. Nếu button workflow label nói "Trả lại" nhưng phiếu vẫn tiến approve → audit FE `isReject` payload condition vs button `isSendBack` label condition vs dialog `isSendBack` warning condition — phải sync 3 chỗ với CÙNG set target phase. BE thêm guard `(target ∈ terminalSet) ⇔ (decision=Reject)` chặn caller mismatch (#45)

fe-admin/src/components/pe/PeDetailTabs.tsx

@@ -15,6 +15,7 @@ import { Select } from '@/components/ui/Select'
 import { api } from '@/lib/api'
 import { getErrorMessage } from '@/lib/apiError'
 import { cn } from '@/lib/cn'
+import { useAuth } from '@/contexts/AuthContext'
 import {
   PeAttachmentPurpose,
   PeAttachmentPurposeLabel,
@@ -100,17 +101,33 @@ export function PeDetailTabs({
   const canEditPhase = isEditablePhase(evaluation.phase)
   const opinionsReadOnly = readOnly || mode === 'workspace'
 
+  // Mig 28 (S21 t4) — F3: Approver edit Section 2 (Hạng mục + NCC + Báo giá).
+  const { user: currentUser } = useAuth()
+  const isAdmin = currentUser?.roles?.includes('Admin') ?? false
+  const v2Approvers = evaluation.currentApproval?.approvers ?? []
+  const actorMatchesLevel = isAdmin
+    || (currentUser?.id != null && v2Approvers.some(a => a.userId === currentUser.id))
+  const approverEditMode = evaluation.phase === PurchaseEvaluationPhase.ChoDuyet
+    && (evaluation.workflowOptions?.allowApproverEditDetails ?? false)
+    && actorMatchesLevel
+  const itemsReadOnly = readOnly && !approverEditMode
+
   // "Lưu & Gửi Duyệt" workspace mode (user 2026-05-07): trigger transition
   // sang phase tiếp theo (= Đã gửi duyệt). nextPhases[0] thường là ChoPurchasing
   // (skip TuChoi). Sau success → toast + invalidate + onBack đóng workspace.
+  // Mig 28 (S21 t4) — F2: Drafter skip thẳng Cấp cuối. Workflow phải bật flag.
+  const [skipToFinal, setSkipToFinal] = useState(false)
+  const allowSkipToFinal = evaluation.workflowOptions?.allowDrafterSkipToFinal ?? false
+
   const submitForApproval = useMutation({
-    mutationFn: async () => {
+    mutationFn: async (opts: { skipToFinal: boolean }) => {
       const next = evaluation.workflow.nextPhases.find(p => p !== PurchaseEvaluationPhase.TuChoi && p !== PurchaseEvaluationPhase.TraLai)
       if (!next) throw new Error('Không có phase tiếp theo để gửi duyệt')
       return api.post(`/purchase-evaluations/${evaluation.id}/transitions`, {
         targetPhase: next,
         decision: 1,
         comment: null,
+        skipToFinal: opts.skipToFinal,
       })
     },
     onSuccess: () => {
@@ -192,7 +209,14 @@ export function PeDetailTabs({
           <InfoTab ev={evaluation} readOnly={readOnly} autoEdit={autoEditHeader} />
         </Section>
         <Section title={`2. Hạng mục + Báo giá NCC (${evaluation.details.length} hạng mục · ${evaluation.suppliers.length} NCC)`}>
-          <ItemsTab ev={evaluation} readOnly={readOnly} />
+          {/* Mig 28 (S21 t4) — F3: itemsReadOnly cho phép approver edit Section 2 */}
+          {approverEditMode && readOnly && (
+            <div className="mx-5 mt-2 rounded border border-violet-200 bg-violet-50 px-3 py-2 text-[11px] text-violet-800">
+              ⓘ Bạn được phép chỉnh sửa Hạng mục / NCC / Báo giá (workflow bật mode Approver edit).
+              Mọi thay đổi sẽ được ghi vào Lịch sử chỉnh sửa.
+            </div>
+          )}
+          <ItemsTab ev={evaluation} readOnly={itemsReadOnly} />
         </Section>
         <Section title="3. Chọn NCC / TP thắng thầu">
           <ChonNccSection ev={evaluation} readOnly={readOnly} />
@@ -251,18 +275,33 @@ export function PeDetailTabs({
             >
               Lưu
             </Button>
+            {/* Mig 28 (S21 t4) — F2: Drafter skip checkbox */}
+            {allowSkipToFinal && canSubmitForApproval && (
+              <label className="flex cursor-pointer items-center gap-1.5 rounded border border-violet-200 bg-violet-50 px-2 py-1 text-[11px] text-violet-800">
+                <input
+                  type="checkbox"
+                  className="h-3 w-3"
+                  checked={skipToFinal}
+                  onChange={e => setSkipToFinal(e.target.checked)}
+                />
+                <span>Gửi thẳng Cấp cuối (skip trung gian)</span>
+              </label>
+            )}
             <Button
               onClick={() => {
                 if (!forwardPhase) return
-                if (confirm(`Gửi phiếu vào quy trình duyệt? Sẽ chuyển sang "${PurchaseEvaluationPhaseLabel[forwardPhase]}". Sau khi gửi sẽ KHÔNG sửa được nữa (trừ khi approver Trả lại).`)) {
+                const confirmMsg = skipToFinal
-                  submitForApproval.mutate()
+                  ? `Gửi THẲNG CẤP CUỐI bỏ qua các Cấp trung gian? Hệ thống sẽ ghi audit "Drafter skip" — không quay lại được trừ khi approver Trả lại.`
+                  : `Gửi phiếu vào quy trình duyệt? Sẽ chuyển sang "${PurchaseEvaluationPhaseLabel[forwardPhase]}". Sau khi gửi sẽ KHÔNG sửa được nữa (trừ khi approver Trả lại).`
+                if (confirm(confirmMsg)) {
+                  submitForApproval.mutate({ skipToFinal })
                 }
               }}
               disabled={!canSubmitForApproval || submitForApproval.isPending}
               title={submitDisabledReason ?? `Gửi phiếu sang "${forwardPhase ? PurchaseEvaluationPhaseLabel[forwardPhase] : '?'}"`}
               className="text-xs"
             >
-              {submitForApproval.isPending ? 'Đang gửi…' : 'Lưu & Gửi Duyệt →'}
+              {submitForApproval.isPending ? 'Đang gửi…' : skipToFinal ? 'Lưu & Gửi thẳng CẤP CUỐI →' : 'Lưu & Gửi Duyệt →'}
             </Button>
           </div>
         </div>

fe-admin/src/components/pe/PeWorkflowPanel.tsx

@@ -18,6 +18,7 @@ import {
   PurchaseEvaluationPhase,
   PurchaseEvaluationPhaseColor,
   PurchaseEvaluationPhaseLabel,
+  WorkflowReturnMode,
   type PeDepartmentApproval,
   type PeDetailBundle,
 } from '@/types/purchaseEvaluation'
@@ -33,10 +34,20 @@ export function PeWorkflowPanel({
 }) {
   const [target, setTarget] = useState<number | null>(null)
   const [comment, setComment] = useState('')
+  // Mig 28 (S21 t4) — F1 mode Trả lại. Default Drafter (backward compat S17).
+  const [returnMode, setReturnMode] = useState<WorkflowReturnMode>(WorkflowReturnMode.Drafter)
+  const [returnTargetUserId, setReturnTargetUserId] = useState<string | null>(null)
   const qc = useQueryClient()
   const { user: currentUser } = useAuth()
   const isAdmin = currentUser?.roles?.includes('Admin') ?? false
 
+  // Mig 28 — F1 workflow options. Null nếu V1 legacy → fallback chỉ "Trả về Drafter".
+  const wfOptions = evaluation.workflowOptions
+  // List approvers đã ký (cho mode Assignee dropdown pick)
+  const signedApprovers = (evaluation.levelOpinions ?? [])
+    .map(o => ({ userId: o.approverUserId, fullName: o.approverFullName ?? 'NV' }))
+    .filter((v, i, arr) => arr.findIndex(x => x.userId === v.userId) === i)
+
   // Mig 24 — V2 schema chỉ cho phép approver trong CurrentApproval.approvers
   // duyệt cấp hiện tại. Nếu actor không khớp → disable nút "Duyệt forward"
   // (Trả lại / Từ chối vẫn enabled vì Service không kiểm Bước/Cấp với 2
@@ -63,15 +74,28 @@ export function PeWorkflowPanel({
     mutationFn: async () => {
       // Decision = Reject (2) khi:
       //  - target = TuChoi (huỷ phiếu)
-      //  - target = DangSoanThao từ phase trung gian (= Trả lại — smart reject Mig 16
+      //  - target = DangSoanThao từ phase trung gian (= Trả lại legacy Mig 16
       //    set RejectedFromPhase + clear N-stage rows + Drafter resume jump-back)
+      //  - target = TraLai (98) từ phase trung gian — Session 17 spec mới: Trả
+      //    lại là Phase RIÊNG (gotcha #45 — thiếu nhánh này gây "Trả về nhưng
+      //    hệ thống vẫn duyệt" do BE nhận decision=Approve → ApproveV2Async).
+      // BE có guard mirror trong PurchaseEvaluationWorkflowService.TransitionAsync
+      // throw ConflictException nếu payload mismatch — phải sync 2 phía.
       const isReject = target === PurchaseEvaluationPhase.TuChoi
         || (target === PurchaseEvaluationPhase.DangSoanThao
             && evaluation.phase !== PurchaseEvaluationPhase.DangSoanThao)
+        || (target === PurchaseEvaluationPhase.TraLai
+            && evaluation.phase !== PurchaseEvaluationPhase.TraLai)
+      // Mig 28 (S21 t4) — F1: chỉ gửi returnMode khi target=TraLai + mode != null
+      const isTraLaiAction = target === PurchaseEvaluationPhase.TraLai
+        && evaluation.phase !== PurchaseEvaluationPhase.TraLai
       return api.post(`/purchase-evaluations/${evaluation.id}/transitions`, {
         targetPhase: target,
         decision: isReject ? 2 : 1,
         comment: comment || null,
+        returnMode: isTraLaiAction ? returnMode : null,
+        returnTargetUserId: isTraLaiAction && returnMode === WorkflowReturnMode.Assignee
+          ? returnTargetUserId : null,
       })
     },
     onSuccess: () => {
@@ -81,6 +105,8 @@ export function PeWorkflowPanel({
       qc.invalidateQueries({ queryKey: ['pe-dept-approvals', evaluation.id] })
       setTarget(null)
       setComment('')
+      setReturnMode(WorkflowReturnMode.Drafter)
+      setReturnTargetUserId(null)
     },
     onError: e => toast.error(getErrorMessage(e)),
   })
@@ -250,8 +276,13 @@ export function PeWorkflowPanel({
 
       {target !== null && (() => {
         const isCancel = target === PurchaseEvaluationPhase.TuChoi
-        const isSendBack = target === PurchaseEvaluationPhase.DangSoanThao
+        // isSendBack sync với button label + payload isReject (gotcha #45).
+        // Include cả DangSoanThao (legacy Mig 16) lẫn TraLai (Session 17 spec)
+        // — cả 2 là Trả lại Drafter sửa.
+        const isSendBack = (target === PurchaseEvaluationPhase.DangSoanThao
+                            || target === PurchaseEvaluationPhase.TraLai)
           && evaluation.phase !== PurchaseEvaluationPhase.DangSoanThao
+          && evaluation.phase !== PurchaseEvaluationPhase.TraLai
         const dialogTitle = isCancel
           ? '✗ Từ chối phiếu (khoá hoàn toàn)'
           : isSendBack
@@ -273,9 +304,96 @@ export function PeWorkflowPanel({
               </div>
             )}
             {isSendBack && (
-              <div className="mb-3 rounded border border-amber-200 bg-amber-50 px-3 py-2 text-[11px] text-amber-800">
+              <>
-                Phiếu sẽ về &ldquo;Đang soạn thảo&rdquo;. Drafter có thể sửa rồi trình lại — workflow tự jump tới phase này.
+                {/* Mig 28 (S21 t4) — F1 mode picker khi Trả lại. Show modes
+                    enabled per workflow.options. Default Drafter (S17 fallback). */}
+                {(wfOptions?.allowReturnOneLevel
+                  || wfOptions?.allowReturnOneStep
+                  || wfOptions?.allowReturnToAssignee
+                  || wfOptions?.allowReturnToDrafter
+                  || !wfOptions) && (
+                  <div className="mb-3 space-y-1.5">
+                    <Label className="text-[12px]">Chọn cách Trả lại</Label>
+                    <div className="space-y-1">
+                      {(wfOptions?.allowReturnOneLevel) && (
+                        <label className="flex items-start gap-2 rounded border border-amber-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                          <input
+                            type="radio"
+                            className="mt-0.5"
+                            checked={returnMode === WorkflowReturnMode.OneLevel}
+                            onChange={() => setReturnMode(WorkflowReturnMode.OneLevel)}
+                          />
+                          <span>
+                            <span className="font-medium">Trả về 1 Cấp trước</span>
+                            <span className="block text-[10px] text-slate-500">Lùi 1 Cấp trong cùng Bước. NV cấp trước nhận lại.</span>
+                          </span>
+                        </label>
+                      )}
+                      {(wfOptions?.allowReturnOneStep) && (
+                        <label className="flex items-start gap-2 rounded border border-amber-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                          <input
+                            type="radio"
+                            className="mt-0.5"
+                            checked={returnMode === WorkflowReturnMode.OneStep}
+                            onChange={() => setReturnMode(WorkflowReturnMode.OneStep)}
+                          />
+                          <span>
+                            <span className="font-medium">Trả về 1 Bước trước</span>
+                            <span className="block text-[10px] text-slate-500">Lùi sang Bước trước, NV Cấp cuối Bước đó nhận lại.</span>
+                          </span>
+                        </label>
+                      )}
+                      {(wfOptions?.allowReturnToAssignee) && (
+                        <label className="flex items-start gap-2 rounded border border-amber-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                          <input
+                            type="radio"
+                            className="mt-0.5"
+                            checked={returnMode === WorkflowReturnMode.Assignee}
+                            onChange={() => setReturnMode(WorkflowReturnMode.Assignee)}
+                          />
+                          <span className="flex-1">
+                            <span className="font-medium">Trả về Người chỉ định</span>
+                            <span className="block text-[10px] text-slate-500">Pick từ list NV đã duyệt trước đó. Workflow set Cấp/Bước của NV.</span>
+                            {returnMode === WorkflowReturnMode.Assignee && (
+                              <select
+                                className="mt-1.5 w-full rounded border border-slate-300 px-2 py-1 text-[12px]"
+                                value={returnTargetUserId ?? ''}
+                                onChange={e => setReturnTargetUserId(e.target.value || null)}
+                              >
+                                <option value="">— Chọn NV —</option>
+                                {signedApprovers.map(a => (
+                                  <option key={a.userId} value={a.userId}>{a.fullName}</option>
+                                ))}
+                              </select>
+                            )}
+                          </span>
+                        </label>
+                      )}
+                      {(wfOptions?.allowReturnToDrafter !== false) && (
+                        <label className="flex items-start gap-2 rounded border border-amber-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                          <input
+                            type="radio"
+                            className="mt-0.5"
+                            checked={returnMode === WorkflowReturnMode.Drafter}
+                            onChange={() => setReturnMode(WorkflowReturnMode.Drafter)}
+                          />
+                          <span>
+                            <span className="font-medium">Trả về Người soạn thảo (mặc định)</span>
+                            <span className="block text-[10px] text-slate-500">Phase → "Trả lại". Drafter sửa rồi gửi lại chạy từ Cấp 1 Bước 1.</span>
+                          </span>
+                        </label>
+                      )}
                     </div>
+                  </div>
+                )}
+                <div className="mb-3 rounded border border-amber-200 bg-amber-50 px-3 py-2 text-[11px] text-amber-800">
+                  {returnMode === WorkflowReturnMode.Drafter
+                    ? 'Phiếu sẽ về "Trả lại". Drafter có thể sửa rồi trình lại từ Cấp 1 Bước 1.'
+                    : returnMode === WorkflowReturnMode.Assignee
+                      ? 'Phiếu sẽ về Cấp/Bước của NV đã chọn (vẫn "Đã gửi duyệt"). NV nhận lại để duyệt tiếp.'
+                      : 'Phiếu sẽ lùi pointer (vẫn "Đã gửi duyệt"). NV trước nhận lại để duyệt tiếp.'}
+                </div>
+              </>
             )}
             <Label>Ghi chú (tùy chọn)</Label>
             <Textarea value={comment} onChange={e => setComment(e.target.value)} rows={3} />

fe-admin/src/pages/system/ApprovalWorkflowsV2Page.tsx

@@ -60,6 +60,13 @@ type DefinitionDto = {
   description: string | null
   isActive: boolean
   isUserSelectable: boolean    // Mig 25 — admin toggle cho user pick
+  // Mig 28 (S21 t4) — 6 advanced options per workflow version
+  allowReturnOneLevel: boolean
+  allowReturnOneStep: boolean
+  allowReturnToAssignee: boolean
+  allowReturnToDrafter: boolean        // default true backward compat S17
+  allowDrafterSkipToFinal: boolean
+  allowApproverEditDetails: boolean
   activatedAt: string | null
   createdAt: string
   steps: StepDto[]
@@ -445,6 +452,15 @@ function Designer({
   const [description, setDescription] = useState(cloneFrom?.description ?? '')
   const [steps, setSteps] = useState<EditStep[]>(initialSteps)
 
+  // Mig 28 (S21 t4) — 6 advanced options. Default clone từ cloneFrom (giữ
+  // config version trước) hoặc backward compat S17 (chỉ Drafter mode).
+  const [allowReturnOneLevel, setAllowReturnOneLevel] = useState(cloneFrom?.allowReturnOneLevel ?? false)
+  const [allowReturnOneStep, setAllowReturnOneStep] = useState(cloneFrom?.allowReturnOneStep ?? false)
+  const [allowReturnToAssignee, setAllowReturnToAssignee] = useState(cloneFrom?.allowReturnToAssignee ?? false)
+  const [allowReturnToDrafter, setAllowReturnToDrafter] = useState(cloneFrom?.allowReturnToDrafter ?? true)
+  const [allowDrafterSkipToFinal, setAllowDrafterSkipToFinal] = useState(cloneFrom?.allowDrafterSkipToFinal ?? false)
+  const [allowApproverEditDetails, setAllowApproverEditDetails] = useState(cloneFrom?.allowApproverEditDetails ?? false)
+
   const usersList = useQuery({
     queryKey: ['users-for-approver-v2'],
     queryFn: async () =>
@@ -503,6 +519,13 @@ function Designer({
             approverUserId: e.approverUserId,
           })),
         })),
+        // Mig 28 (S21 t4) — 6 advanced options
+        allowReturnOneLevel,
+        allowReturnOneStep,
+        allowReturnToAssignee,
+        allowReturnToDrafter,
+        allowDrafterSkipToFinal,
+        allowApproverEditDetails,
       })
     },
     onSuccess: () => {
@@ -561,6 +584,118 @@ function Designer({
           </div>
         </div>
 
+        {/* Mig 28 (S21 t4) — Section Cấu hình nâng cao (F1+F2+F3 advanced options).
+            6 checkbox per workflow: 4 mode Trả lại + 1 Skip CEO + 1 Approver edit. */}
+        <div className="space-y-2 rounded-lg border border-amber-200 bg-amber-50/30 p-3">
+          <Label className="text-amber-900">
+            Cấu hình nâng cao — quyền duyệt mở rộng
+          </Label>
+          <p className="text-[11px] leading-relaxed text-slate-600">
+            Bật/tắt mode duyệt mở rộng cho workflow này. Mặc định chỉ "Trả về Người soạn thảo" enabled
+            (tương thích quy trình cũ). Các mode khác opt-in để audit nghiêm.
+          </p>
+
+          <div className="mt-2 space-y-3">
+            <div>
+              <div className="mb-1 text-[11px] font-semibold uppercase text-slate-500">
+                Mode Trả lại (Approver chọn khi nhấn ← Trả lại)
+              </div>
+              <div className="grid grid-cols-2 gap-1.5">
+                <label className="flex items-start gap-2 rounded border border-slate-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                  <input
+                    type="checkbox"
+                    className="mt-0.5 h-3.5 w-3.5"
+                    checked={allowReturnOneLevel}
+                    onChange={e => setAllowReturnOneLevel(e.target.checked)}
+                  />
+                  <span>
+                    <span className="font-medium">Trả về 1 Cấp trước</span>
+                    <span className="block text-[10px] text-slate-500">Lùi 1 Cấp trong cùng Bước, peer review chain</span>
+                  </span>
+                </label>
+                <label className="flex items-start gap-2 rounded border border-slate-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                  <input
+                    type="checkbox"
+                    className="mt-0.5 h-3.5 w-3.5"
+                    checked={allowReturnOneStep}
+                    onChange={e => setAllowReturnOneStep(e.target.checked)}
+                  />
+                  <span>
+                    <span className="font-medium">Trả về 1 Bước trước</span>
+                    <span className="block text-[10px] text-slate-500">Lùi sang Bước trước, Cấp cuối nhận lại</span>
+                  </span>
+                </label>
+                <label className="flex items-start gap-2 rounded border border-slate-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                  <input
+                    type="checkbox"
+                    className="mt-0.5 h-3.5 w-3.5"
+                    checked={allowReturnToAssignee}
+                    onChange={e => setAllowReturnToAssignee(e.target.checked)}
+                  />
+                  <span>
+                    <span className="font-medium">Trả về Người chỉ định</span>
+                    <span className="block text-[10px] text-slate-500">Pick runtime từ list NV đã duyệt</span>
+                  </span>
+                </label>
+                <label className="flex items-start gap-2 rounded border border-slate-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                  <input
+                    type="checkbox"
+                    className="mt-0.5 h-3.5 w-3.5"
+                    checked={allowReturnToDrafter}
+                    onChange={e => setAllowReturnToDrafter(e.target.checked)}
+                  />
+                  <span>
+                    <span className="font-medium">Trả về Người soạn thảo</span>
+                    <span className="block text-[10px] text-slate-500">Phase=TraLai, Drafter sửa rồi gửi lại (mặc định)</span>
+                  </span>
+                </label>
+              </div>
+            </div>
+
+            <div>
+              <div className="mb-1 text-[11px] font-semibold uppercase text-slate-500">
+                Drafter gửi duyệt (Workspace "Lưu &amp; Gửi Duyệt")
+              </div>
+              <label className="flex items-start gap-2 rounded border border-slate-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                <input
+                  type="checkbox"
+                  className="mt-0.5 h-3.5 w-3.5"
+                  checked={allowDrafterSkipToFinal}
+                  onChange={e => setAllowDrafterSkipToFinal(e.target.checked)}
+                />
+                <span>
+                  <span className="font-medium">Cho phép Drafter gửi thẳng Cấp cuối</span>
+                  <span className="block text-[10px] text-slate-500">
+                    Skip mọi Bước/Cấp trung gian → đi thẳng NV Cấp cuối (vd CEO).
+                    Workspace hiện dropdown 2 option "Gửi tuần tự" vs "Gửi thẳng Cấp cuối".
+                  </span>
+                </span>
+              </label>
+            </div>
+
+            <div>
+              <div className="mb-1 text-[11px] font-semibold uppercase text-slate-500">
+                Approver chỉnh sửa phiếu
+              </div>
+              <label className="flex items-start gap-2 rounded border border-slate-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                <input
+                  type="checkbox"
+                  className="mt-0.5 h-3.5 w-3.5"
+                  checked={allowApproverEditDetails}
+                  onChange={e => setAllowApproverEditDetails(e.target.checked)}
+                />
+                <span>
+                  <span className="font-medium">Cho phép Approver chỉnh sửa Section 2 (Hạng mục + NCC + Báo giá)</span>
+                  <span className="block text-[10px] text-slate-500">
+                    NV Cấp đang duyệt được edit chi tiết phiếu (không reset workflow,
+                    giữ Cấp hiện tại). Mọi thay đổi log vào Lịch sử chỉnh sửa.
+                  </span>
+                </span>
+              </label>
+            </div>
+          </div>
+        </div>
+
         <div className="space-y-2 rounded-lg border border-slate-200 p-3">
           <div className="flex items-center justify-between">
             <Label>

fe-admin/src/types/purchaseEvaluation.ts

@@ -347,6 +347,25 @@ export type PeDepartmentApproval = {
   isBypassed: boolean
 }
 
+// Mig 28 (S21 t4) — 6 advanced options của workflow pin.
+export type ApprovalWorkflowOptions = {
+  allowReturnOneLevel: boolean
+  allowReturnOneStep: boolean
+  allowReturnToAssignee: boolean
+  allowReturnToDrafter: boolean
+  allowDrafterSkipToFinal: boolean
+  allowApproverEditDetails: boolean
+}
+
+// Mig 28 (S21 t4) — F1 mode Trả lại payload gửi BE
+export const WorkflowReturnMode = {
+  OneLevel: 1,
+  OneStep: 2,
+  Assignee: 3,
+  Drafter: 4,
+} as const
+export type WorkflowReturnMode = typeof WorkflowReturnMode[keyof typeof WorkflowReturnMode]
+
 export type PeDetailBundle = {
   id: string
   maPhieu: string | null
@@ -378,6 +397,8 @@ export type PeDetailBundle = {
   approvalWorkflowCode: string | null
   approvalWorkflowName: string | null
   approvalWorkflowVersion: number | null
+  // Mig 28 (S21 t4) — 6 advanced options của workflow pin. Null nếu V1 legacy.
+  workflowOptions: ApprovalWorkflowOptions | null
   // Mig 24 — info Bước/Cấp đang chờ duyệt (chỉ populate khi pin V2 + Phase=ChoDuyet)
   currentApproval: PeCurrentApproval | null
   // Mig 24 — full flow snapshot (Bước → Cấp → NV) với Status per level

fe-user/src/components/pe/PeDetailTabs.tsx

@@ -15,6 +15,7 @@ import { Select } from '@/components/ui/Select'
 import { api } from '@/lib/api'
 import { getErrorMessage } from '@/lib/apiError'
 import { cn } from '@/lib/cn'
+import { useAuth } from '@/contexts/AuthContext'
 import {
   PeAttachmentPurpose,
   PeAttachmentPurposeLabel,
@@ -100,17 +101,38 @@ export function PeDetailTabs({
   const canEditPhase = isEditablePhase(evaluation.phase)
   const opinionsReadOnly = readOnly || mode === 'workspace'
 
+  // Mig 28 (S21 t4) — F3: Approver edit Section 2 (Hạng mục + NCC + Báo giá).
+  // Khi phase=ChoDuyet + workflow.AllowApproverEditDetails + actor match
+  // CurrentLevel.ApproverUserId → cho phép edit Section 2 dù readOnly=true.
+  const { user: currentUser } = useAuth()
+  const isAdmin = currentUser?.roles?.includes('Admin') ?? false
+  const v2Approvers = evaluation.currentApproval?.approvers ?? []
+  const actorMatchesLevel = isAdmin
+    || (currentUser?.id != null && v2Approvers.some(a => a.userId === currentUser.id))
+  const approverEditMode = evaluation.phase === PurchaseEvaluationPhase.ChoDuyet
+    && (evaluation.workflowOptions?.allowApproverEditDetails ?? false)
+    && actorMatchesLevel
+  // itemsReadOnly = readOnly trừ khi approver mode F3 mở
+  const itemsReadOnly = readOnly && !approverEditMode
+
+  // Mig 28 (S21 t4) — F2: Drafter skip thẳng Cấp cuối. Workflow phải bật flag.
+  // Default false (gửi tuần tự như cũ). Sync state với confirm dialog handler.
+  const [skipToFinal, setSkipToFinal] = useState(false)
+  const allowSkipToFinal = evaluation.workflowOptions?.allowDrafterSkipToFinal ?? false
+
   // "Lưu & Gửi Duyệt" workspace mode (user 2026-05-07): trigger transition
   // sang phase tiếp theo (= Đã gửi duyệt). nextPhases[0] thường là ChoPurchasing
   // (skip TuChoi). Sau success → toast + invalidate + onBack đóng workspace.
   const submitForApproval = useMutation({
-    mutationFn: async () => {
+    mutationFn: async (opts: { skipToFinal: boolean }) => {
       const next = evaluation.workflow.nextPhases.find(p => p !== PurchaseEvaluationPhase.TuChoi && p !== PurchaseEvaluationPhase.TraLai)
       if (!next) throw new Error('Không có phase tiếp theo để gửi duyệt')
       return api.post(`/purchase-evaluations/${evaluation.id}/transitions`, {
         targetPhase: next,
         decision: 1,
         comment: null,
+        // Mig 28 (S21 t4) — F2: Drafter skip thẳng Cấp cuối
+        skipToFinal: opts.skipToFinal,
       })
     },
     onSuccess: () => {
@@ -192,7 +214,15 @@ export function PeDetailTabs({
           <InfoTab ev={evaluation} readOnly={readOnly} autoEdit={autoEditHeader} />
         </Section>
         <Section title={`2. Hạng mục + Báo giá NCC (${evaluation.details.length} hạng mục · ${evaluation.suppliers.length} NCC)`}>
-          <ItemsTab ev={evaluation} readOnly={readOnly} />
+          {/* Mig 28 (S21 t4) — F3: itemsReadOnly cho phép approver edit Section 2.
+              Banner cảnh báo "Bạn đang chỉnh sửa khi đang duyệt" khi approverEditMode. */}
+          {approverEditMode && readOnly && (
+            <div className="mx-5 mt-2 rounded border border-violet-200 bg-violet-50 px-3 py-2 text-[11px] text-violet-800">
+              ⓘ Bạn được phép chỉnh sửa Hạng mục / NCC / Báo giá (workflow bật mode Approver edit).
+              Mọi thay đổi sẽ được ghi vào Lịch sử chỉnh sửa.
+            </div>
+          )}
+          <ItemsTab ev={evaluation} readOnly={itemsReadOnly} />
         </Section>
         <Section title="3. Chọn NCC / TP thắng thầu">
           <ChonNccSection ev={evaluation} readOnly={readOnly} />
@@ -251,18 +281,34 @@ export function PeDetailTabs({
             >
               Lưu
             </Button>
+            {/* Mig 28 (S21 t4) — F2: Drafter skip thẳng Cấp cuối checkbox.
+                Chỉ hiện khi workflow.AllowDrafterSkipToFinal=true. */}
+            {allowSkipToFinal && canSubmitForApproval && (
+              <label className="flex cursor-pointer items-center gap-1.5 rounded border border-violet-200 bg-violet-50 px-2 py-1 text-[11px] text-violet-800">
+                <input
+                  type="checkbox"
+                  className="h-3 w-3"
+                  checked={skipToFinal}
+                  onChange={e => setSkipToFinal(e.target.checked)}
+                />
+                <span>Gửi thẳng Cấp cuối (skip trung gian)</span>
+              </label>
+            )}
             <Button
               onClick={() => {
                 if (!forwardPhase) return
-                if (confirm(`Gửi phiếu vào quy trình duyệt? Sẽ chuyển sang "${PurchaseEvaluationPhaseLabel[forwardPhase]}". Sau khi gửi sẽ KHÔNG sửa được nữa (trừ khi approver Trả lại).`)) {
+                const confirmMsg = skipToFinal
-                  submitForApproval.mutate()
+                  ? `Gửi THẲNG CẤP CUỐI bỏ qua các Cấp trung gian? Hệ thống sẽ ghi audit "Drafter skip" — không quay lại được trừ khi approver Trả lại.`
+                  : `Gửi phiếu vào quy trình duyệt? Sẽ chuyển sang "${PurchaseEvaluationPhaseLabel[forwardPhase]}". Sau khi gửi sẽ KHÔNG sửa được nữa (trừ khi approver Trả lại).`
+                if (confirm(confirmMsg)) {
+                  submitForApproval.mutate({ skipToFinal })
                 }
               }}
               disabled={!canSubmitForApproval || submitForApproval.isPending}
               title={submitDisabledReason ?? `Gửi phiếu sang "${forwardPhase ? PurchaseEvaluationPhaseLabel[forwardPhase] : '?'}"`}
               className="text-xs"
             >
-              {submitForApproval.isPending ? 'Đang gửi…' : 'Lưu & Gửi Duyệt →'}
+              {submitForApproval.isPending ? 'Đang gửi…' : skipToFinal ? 'Lưu & Gửi thẳng CẤP CUỐI →' : 'Lưu & Gửi Duyệt →'}
             </Button>
           </div>
         </div>

fe-user/src/components/pe/PeWorkflowPanel.tsx

@@ -18,6 +18,7 @@ import {
   PurchaseEvaluationPhase,
   PurchaseEvaluationPhaseColor,
   PurchaseEvaluationPhaseLabel,
+  WorkflowReturnMode,
   type PeDepartmentApproval,
   type PeDetailBundle,
 } from '@/types/purchaseEvaluation'
@@ -33,10 +34,21 @@ export function PeWorkflowPanel({
 }) {
   const [target, setTarget] = useState<number | null>(null)
   const [comment, setComment] = useState('')
+  // Mig 28 (S21 t4) — F1 mode Trả lại. Default Drafter (backward compat S17).
+  const [returnMode, setReturnMode] = useState<WorkflowReturnMode>(WorkflowReturnMode.Drafter)
+  const [returnTargetUserId, setReturnTargetUserId] = useState<string | null>(null)
   const qc = useQueryClient()
   const { user: currentUser } = useAuth()
   const isAdmin = currentUser?.roles?.includes('Admin') ?? false
 
+  // Mig 28 — F1 workflow options. Null nếu V1 legacy → fallback chỉ "Trả về Drafter".
+  const wfOptions = evaluation.workflowOptions
+  // List approvers đã ký (cho mode Assignee dropdown pick)
+  const signedApprovers = (evaluation.levelOpinions ?? [])
+    .map(o => ({ userId: o.approverUserId, fullName: o.approverFullName ?? 'NV' }))
+    // Dedupe by userId (1 NV có thể ký nhiều cấp nếu workflow đặt như vậy)
+    .filter((v, i, arr) => arr.findIndex(x => x.userId === v.userId) === i)
+
   // Mig 24 — V2 schema chỉ cho phép approver trong CurrentApproval.approvers
   // duyệt cấp hiện tại. Admin bypass.
   const v2Approvers = evaluation.currentApproval?.approvers ?? []
@@ -59,15 +71,28 @@ export function PeWorkflowPanel({
     mutationFn: async () => {
       // Decision = Reject (2) khi:
       //  - target = TuChoi (huỷ phiếu)
-      //  - target = DangSoanThao từ phase trung gian (= Trả lại — smart reject Mig 16
+      //  - target = DangSoanThao từ phase trung gian (= Trả lại legacy Mig 16
       //    set RejectedFromPhase + clear N-stage rows + Drafter resume jump-back)
+      //  - target = TraLai (98) từ phase trung gian — Session 17 spec mới: Trả
+      //    lại là Phase RIÊNG (gotcha #45 — thiếu nhánh này gây "Trả về nhưng
+      //    hệ thống vẫn duyệt" do BE nhận decision=Approve → ApproveV2Async).
+      // BE có guard mirror trong PurchaseEvaluationWorkflowService.TransitionAsync
+      // throw ConflictException nếu payload mismatch — phải sync 2 phía.
       const isReject = target === PurchaseEvaluationPhase.TuChoi
         || (target === PurchaseEvaluationPhase.DangSoanThao
             && evaluation.phase !== PurchaseEvaluationPhase.DangSoanThao)
+        || (target === PurchaseEvaluationPhase.TraLai
+            && evaluation.phase !== PurchaseEvaluationPhase.TraLai)
+      // Mig 28 (S21 t4) — F1: chỉ gửi returnMode khi target=TraLai + mode != null
+      const isTraLaiAction = target === PurchaseEvaluationPhase.TraLai
+        && evaluation.phase !== PurchaseEvaluationPhase.TraLai
       return api.post(`/purchase-evaluations/${evaluation.id}/transitions`, {
         targetPhase: target,
         decision: isReject ? 2 : 1,
         comment: comment || null,
+        returnMode: isTraLaiAction ? returnMode : null,
+        returnTargetUserId: isTraLaiAction && returnMode === WorkflowReturnMode.Assignee
+          ? returnTargetUserId : null,
       })
     },
     onSuccess: () => {
@@ -77,6 +102,8 @@ export function PeWorkflowPanel({
       qc.invalidateQueries({ queryKey: ['pe-dept-approvals', evaluation.id] })
       setTarget(null)
       setComment('')
+      setReturnMode(WorkflowReturnMode.Drafter)
+      setReturnTargetUserId(null)
     },
     onError: e => toast.error(getErrorMessage(e)),
   })
@@ -244,8 +271,13 @@ export function PeWorkflowPanel({
 
       {target !== null && (() => {
         const isCancel = target === PurchaseEvaluationPhase.TuChoi
-        const isSendBack = target === PurchaseEvaluationPhase.DangSoanThao
+        // isSendBack sync với button label L205-207 + payload isReject L64-68
+        // (gotcha #45). Include cả DangSoanThao (legacy Mig 16) lẫn TraLai
+        // (Session 17 spec) — cả 2 là Trả lại Drafter sửa.
+        const isSendBack = (target === PurchaseEvaluationPhase.DangSoanThao
+                            || target === PurchaseEvaluationPhase.TraLai)
           && evaluation.phase !== PurchaseEvaluationPhase.DangSoanThao
+          && evaluation.phase !== PurchaseEvaluationPhase.TraLai
         const dialogTitle = isCancel
           ? '✗ Từ chối phiếu (khoá hoàn toàn)'
           : isSendBack
@@ -267,9 +299,96 @@ export function PeWorkflowPanel({
               </div>
             )}
             {isSendBack && (
-              <div className="mb-3 rounded border border-amber-200 bg-amber-50 px-3 py-2 text-[11px] text-amber-800">
+              <>
-                Phiếu sẽ về &ldquo;Đang soạn thảo&rdquo;. Drafter có thể sửa rồi trình lại — workflow tự jump tới phase này.
+                {/* Mig 28 (S21 t4) — F1 mode picker khi Trả lại. Show modes
+                    enabled per workflow.options. Default Drafter (S17 fallback). */}
+                {(wfOptions?.allowReturnOneLevel
+                  || wfOptions?.allowReturnOneStep
+                  || wfOptions?.allowReturnToAssignee
+                  || wfOptions?.allowReturnToDrafter
+                  || !wfOptions) && (
+                  <div className="mb-3 space-y-1.5">
+                    <Label className="text-[12px]">Chọn cách Trả lại</Label>
+                    <div className="space-y-1">
+                      {(wfOptions?.allowReturnOneLevel) && (
+                        <label className="flex items-start gap-2 rounded border border-amber-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                          <input
+                            type="radio"
+                            className="mt-0.5"
+                            checked={returnMode === WorkflowReturnMode.OneLevel}
+                            onChange={() => setReturnMode(WorkflowReturnMode.OneLevel)}
+                          />
+                          <span>
+                            <span className="font-medium">Trả về 1 Cấp trước</span>
+                            <span className="block text-[10px] text-slate-500">Lùi 1 Cấp trong cùng Bước. NV cấp trước nhận lại.</span>
+                          </span>
+                        </label>
+                      )}
+                      {(wfOptions?.allowReturnOneStep) && (
+                        <label className="flex items-start gap-2 rounded border border-amber-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                          <input
+                            type="radio"
+                            className="mt-0.5"
+                            checked={returnMode === WorkflowReturnMode.OneStep}
+                            onChange={() => setReturnMode(WorkflowReturnMode.OneStep)}
+                          />
+                          <span>
+                            <span className="font-medium">Trả về 1 Bước trước</span>
+                            <span className="block text-[10px] text-slate-500">Lùi sang Bước trước, NV Cấp cuối Bước đó nhận lại.</span>
+                          </span>
+                        </label>
+                      )}
+                      {(wfOptions?.allowReturnToAssignee) && (
+                        <label className="flex items-start gap-2 rounded border border-amber-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                          <input
+                            type="radio"
+                            className="mt-0.5"
+                            checked={returnMode === WorkflowReturnMode.Assignee}
+                            onChange={() => setReturnMode(WorkflowReturnMode.Assignee)}
+                          />
+                          <span className="flex-1">
+                            <span className="font-medium">Trả về Người chỉ định</span>
+                            <span className="block text-[10px] text-slate-500">Pick từ list NV đã duyệt trước đó. Workflow set Cấp/Bước của NV.</span>
+                            {returnMode === WorkflowReturnMode.Assignee && (
+                              <select
+                                className="mt-1.5 w-full rounded border border-slate-300 px-2 py-1 text-[12px]"
+                                value={returnTargetUserId ?? ''}
+                                onChange={e => setReturnTargetUserId(e.target.value || null)}
+                              >
+                                <option value="">— Chọn NV —</option>
+                                {signedApprovers.map(a => (
+                                  <option key={a.userId} value={a.userId}>{a.fullName}</option>
+                                ))}
+                              </select>
+                            )}
+                          </span>
+                        </label>
+                      )}
+                      {(wfOptions?.allowReturnToDrafter !== false) && (
+                        <label className="flex items-start gap-2 rounded border border-amber-200 bg-white px-2 py-1.5 text-[12px] hover:bg-amber-50/40">
+                          <input
+                            type="radio"
+                            className="mt-0.5"
+                            checked={returnMode === WorkflowReturnMode.Drafter}
+                            onChange={() => setReturnMode(WorkflowReturnMode.Drafter)}
+                          />
+                          <span>
+                            <span className="font-medium">Trả về Người soạn thảo (mặc định)</span>
+                            <span className="block text-[10px] text-slate-500">Phase → "Trả lại". Drafter sửa rồi gửi lại chạy từ Cấp 1 Bước 1.</span>
+                          </span>
+                        </label>
+                      )}
                     </div>
+                  </div>
+                )}
+                <div className="mb-3 rounded border border-amber-200 bg-amber-50 px-3 py-2 text-[11px] text-amber-800">
+                  {returnMode === WorkflowReturnMode.Drafter
+                    ? 'Phiếu sẽ về "Trả lại". Drafter có thể sửa rồi trình lại từ Cấp 1 Bước 1.'
+                    : returnMode === WorkflowReturnMode.Assignee
+                      ? 'Phiếu sẽ về Cấp/Bước của NV đã chọn (vẫn "Đã gửi duyệt"). NV nhận lại để duyệt tiếp.'
+                      : 'Phiếu sẽ lùi pointer (vẫn "Đã gửi duyệt"). NV trước nhận lại để duyệt tiếp.'}
+                </div>
+              </>
             )}
             <Label>Ghi chú (tùy chọn)</Label>
             <Textarea value={comment} onChange={e => setComment(e.target.value)} rows={3} />

fe-user/src/types/purchaseEvaluation.ts

@@ -344,6 +344,25 @@ export type PeDepartmentApproval = {
   isBypassed: boolean
 }
 
+// Mig 28 (S21 t4) — 6 advanced options của workflow pin.
+export type ApprovalWorkflowOptions = {
+  allowReturnOneLevel: boolean
+  allowReturnOneStep: boolean
+  allowReturnToAssignee: boolean
+  allowReturnToDrafter: boolean
+  allowDrafterSkipToFinal: boolean
+  allowApproverEditDetails: boolean
+}
+
+// Mig 28 (S21 t4) — F1 mode Trả lại payload gửi BE
+export const WorkflowReturnMode = {
+  OneLevel: 1,
+  OneStep: 2,
+  Assignee: 3,
+  Drafter: 4,
+} as const
+export type WorkflowReturnMode = typeof WorkflowReturnMode[keyof typeof WorkflowReturnMode]
+
 export type PeDetailBundle = {
   id: string
   maPhieu: string | null
@@ -375,6 +394,9 @@ export type PeDetailBundle = {
   approvalWorkflowCode: string | null
   approvalWorkflowName: string | null
   approvalWorkflowVersion: number | null
+  // Mig 28 (S21 t4) — 6 advanced options của workflow pin. Null nếu V1 legacy.
+  // FE filter Trả lại dropdown + Skip submit + Edit Section 2 conditional.
+  workflowOptions: ApprovalWorkflowOptions | null
   // Mig 24 — info Bước/Cấp đang chờ duyệt (chỉ populate khi pin V2 + Phase=ChoDuyet)
   currentApproval: PeCurrentApproval | null
   // Mig 24 — full flow snapshot (Bước → Cấp → NV) với Status per level

src/Backend/SolutionErp.Application/ApprovalWorkflowsV2/ApprovalWorkflowV2AdminFeatures.cs

@@ -46,6 +46,15 @@ public record AwDefinitionDto(
     string? Description,
     bool IsActive,
     bool IsUserSelectable,
+    // Mig 28 (S21 t4) — 6 advanced options của workflow per version. Admin
+    // Designer tick stick → checkbox. FE eOffice render dropdown / Skip / Edit
+    // conditional theo flag tương ứng.
+    bool AllowReturnOneLevel,
+    bool AllowReturnOneStep,
+    bool AllowReturnToAssignee,
+    bool AllowReturnToDrafter,
+    bool AllowDrafterSkipToFinal,
+    bool AllowApproverEditDetails,
     DateTime? ActivatedAt,
     DateTime CreatedAt,
     List<AwStepDto> Steps);
@@ -128,6 +137,13 @@ public class GetAwAdminOverviewQueryHandler(
             d.Description,
             d.IsActive,
             d.IsUserSelectable,
+            // Mig 28 — 6 Allow* flag
+            d.AllowReturnOneLevel,
+            d.AllowReturnOneStep,
+            d.AllowReturnToAssignee,
+            d.AllowReturnToDrafter,
+            d.AllowDrafterSkipToFinal,
+            d.AllowApproverEditDetails,
             d.ActivatedAt,
             d.CreatedAt,
             d.Steps.OrderBy(s => s.Order).Select(s => new AwStepDto(
@@ -178,7 +194,15 @@ public record CreateAwDefinitionCommand(
     string Code,
     string Name,
     string? Description,
-    List<CreateAwStepInput> Steps) : IRequest<Guid>;
+    List<CreateAwStepInput> Steps,
+    // Mig 28 (S21 t4) — 6 Allow* options. Default = backward compat S17
+    // (chỉ Trả về Drafter enabled). Admin tick stick để mở mode khác.
+    bool AllowReturnOneLevel = false,
+    bool AllowReturnOneStep = false,
+    bool AllowReturnToAssignee = false,
+    bool AllowReturnToDrafter = true,
+    bool AllowDrafterSkipToFinal = false,
+    bool AllowApproverEditDetails = false) : IRequest<Guid>;
 
 public class CreateAwDefinitionCommandValidator : AbstractValidator<CreateAwDefinitionCommand>
 {
@@ -271,6 +295,13 @@ public class CreateAwDefinitionCommandHandler(IApplicationDbContext db)
             Description = request.Description,
             IsActive = true,
             IsUserSelectable = true,    // Mig 25 — version mới mặc định cho user pick
+            // Mig 28 (S21 t4) — 6 Allow* options
+            AllowReturnOneLevel = request.AllowReturnOneLevel,
+            AllowReturnOneStep = request.AllowReturnOneStep,
+            AllowReturnToAssignee = request.AllowReturnToAssignee,
+            AllowReturnToDrafter = request.AllowReturnToDrafter,
+            AllowDrafterSkipToFinal = request.AllowDrafterSkipToFinal,
+            AllowApproverEditDetails = request.AllowApproverEditDetails,
             ActivatedAt = DateTime.UtcNow,
             Steps = request.Steps.OrderBy(s => s.Order)
                 .Select(s => new ApprovalWorkflowStep

src/Backend/SolutionErp.Application/PurchaseEvaluations/Dtos/PurchaseEvaluationDtos.cs

@@ -78,6 +78,16 @@ public record PurchaseEvaluationChangelogDto(
     string? ContextNote,
     DateTime CreatedAt);
 
+// Mig 28 (S21 t4) — 6 advanced options của workflow pin. FE filter Trả lại
+// dropdown / Skip submit / Edit Section 2 enabled theo flag tương ứng.
+public record ApprovalWorkflowOptionsDto(
+    bool AllowReturnOneLevel,
+    bool AllowReturnOneStep,
+    bool AllowReturnToAssignee,
+    bool AllowReturnToDrafter,
+    bool AllowDrafterSkipToFinal,
+    bool AllowApproverEditDetails);
+
 public record PurchaseEvaluationWorkflowSummaryDto(
     string PolicyName,
     string PolicyDescription,
@@ -194,6 +204,9 @@ public record PurchaseEvaluationDetailBundleDto(
     string? ApprovalWorkflowCode,
     string? ApprovalWorkflowName,
     int? ApprovalWorkflowVersion,
+    // Mig 28 (S21 t4) — 6 Allow* options của workflow pin. Null nếu phiếu V1
+    // legacy. FE render Trả lại dropdown + Skip + Edit Section 2 conditional.
+    ApprovalWorkflowOptionsDto? WorkflowOptions,
     PurchaseEvaluationCurrentApprovalDto? CurrentApproval,
     PurchaseEvaluationApprovalFlowDto? ApprovalFlow,
     List<PurchaseEvaluationSupplierDto> Suppliers,

src/Backend/SolutionErp.Application/PurchaseEvaluations/PurchaseEvaluationDetailFeatures.cs

@@ -4,23 +4,96 @@ using Microsoft.EntityFrameworkCore;
 using SolutionErp.Application.Common.Exceptions;
 using SolutionErp.Application.Common.Interfaces;
 using SolutionErp.Domain.Contracts;
+using SolutionErp.Domain.Identity;
 using SolutionErp.Domain.PurchaseEvaluations;
 
 namespace SolutionErp.Application.PurchaseEvaluations;
 
 // ========== Helper: Lock edit guard (Phase 9 — Migration 16) ==========
-// Chỉ Phase=DangSoanThao mới được CRUD chi tiết / báo giá / NCC tham gia.
+// Original: Chỉ Phase=DangSoanThao mới được CRUD chi tiết / báo giá / NCC tham gia.
 // Đã trình duyệt → KHÔNG sửa được. Phải reject về DangSoanThao trước.
+//
+// Mig 28 (S21 t4 — F3): Extend Section 2 (Detail + NCC + Báo giá) cho phép
+// Approver edit khi phase=ChoDuyet + workflow.AllowApproverEditDetails=true +
+// actor.Id == currentLevel.ApproverUserId. KHÔNG đụng PE Header / Attachment /
+// DepartmentOpinion — vẫn dùng EnsureDraftAsync strict.
 internal static class PurchaseEvaluationDraftGuard
 {
+    /// Strict guard cho PE Header / Attachment / DepartmentOpinion / Winner select —
+    /// chỉ Drafter scope (DangSoanThao OR TraLai để Drafter sửa rồi gửi lại).
     public static async Task<PurchaseEvaluation> EnsureDraftAsync(IApplicationDbContext db, Guid id, CancellationToken ct)
     {
         var pe = await db.PurchaseEvaluations.FirstOrDefaultAsync(x => x.Id == id, ct)
             ?? throw new NotFoundException("PurchaseEvaluation", id);
-        if (pe.Phase != PurchaseEvaluationPhase.DangSoanThao)
+        if (pe.Phase != PurchaseEvaluationPhase.DangSoanThao
-            throw new ConflictException($"Phiếu PE đã trình duyệt (Phase={pe.Phase}), không thể chỉnh sửa chi tiết. Phải reject để Drafter sửa lại.");
+            && pe.Phase != PurchaseEvaluationPhase.TraLai)
+            throw new ConflictException(
+                $"Phiếu PE đã trình duyệt (Phase={pe.Phase}), không thể chỉnh sửa. " +
+                "Phải Trả lại Drafter sửa lại.");
         return pe;
     }
+
+    /// F3 (Mig 28 — S21 t4) — Edit guard cho Section 2 (Detail + NCC + Báo giá).
+    /// 2 trường hợp accepted:
+    ///   1. Drafter scope: DangSoanThao OR TraLai — Controller [Authorize] handle role.
+    ///   2. Approver scope: ChoDuyet + workflow.AllowApproverEditDetails=true +
+    ///      actor.Id match CurrentLevel.ApproverUserId. KHÔNG reset workflow,
+    ///      giữ Cấp hiện tại. Admin bypass workflow flag check.
+    public static async Task<PurchaseEvaluation> EnsureEditableForDetailsAsync(
+        IApplicationDbContext db, Guid id, ICurrentUser currentUser, CancellationToken ct)
+    {
+        var pe = await db.PurchaseEvaluations.FirstOrDefaultAsync(x => x.Id == id, ct)
+            ?? throw new NotFoundException("PurchaseEvaluation", id);
+
+        // Drafter scope — any authenticated, Controller [Authorize(Policy)] gates role
+        if (pe.Phase == PurchaseEvaluationPhase.DangSoanThao
+            || pe.Phase == PurchaseEvaluationPhase.TraLai)
+            return pe;
+
+        // F3 Approver scope (Mig 28) — chỉ ChoDuyet với V2 schema
+        if (pe.Phase == PurchaseEvaluationPhase.ChoDuyet
+            && currentUser.IsAuthenticated
+            && currentUser.UserId is Guid actorUserId)
+        {
+            // Admin bypass — admin có thể edit bất chấp Allow* flag
+            if (currentUser.Roles.Contains(AppRoles.Admin)) return pe;
+
+            // V2 schema required
+            if (pe.ApprovalWorkflowId is Guid awId
+                && pe.CurrentWorkflowStepIndex is int stepIdx
+                && pe.CurrentApprovalLevelOrder is int levelOrder)
+            {
+                var workflow = await db.ApprovalWorkflows
+                    .Include(w => w.Steps).ThenInclude(s => s.Levels)
+                    .FirstOrDefaultAsync(w => w.Id == awId, ct)
+                    ?? throw new ConflictException("Workflow không tồn tại.");
+
+                if (!workflow.AllowApproverEditDetails)
+                    throw new ConflictException(
+                        "Workflow không bật mode 'Approver chỉnh sửa Section 2'. " +
+                        "Phải Trả lại Drafter sửa hoặc liên hệ Admin Designer.");
+
+                var step = workflow.Steps.OrderBy(s => s.Order).Skip(stepIdx).FirstOrDefault();
+                var level = step?.Levels.FirstOrDefault(lv => lv.Order == levelOrder);
+                if (level is null)
+                    throw new ConflictException("Workflow Bước/Cấp không tìm thấy — schema lỗi.");
+
+                if (level.ApproverUserId != actorUserId)
+                    throw new ForbiddenException(
+                        $"Chỉ NV phụ trách Bước {step!.Order} / Cấp {levelOrder} " +
+                        "mới được chỉnh sửa Section 2 lúc đang duyệt.");
+
+                return pe;
+            }
+
+            throw new ConflictException(
+                "Phiếu chưa pin workflow V2 hoặc chưa init Bước/Cấp — không thể chỉnh sửa.");
+        }
+
+        throw new ConflictException(
+            $"Phiếu PE ở Phase={pe.Phase}, không thể chỉnh sửa Section 2. " +
+            "Phải Trả lại Drafter sửa.");
+    }
 }
 
 // ========== Detail (hạng mục + ngân sách) ==========
@@ -55,7 +128,8 @@ public class AddPurchaseEvaluationDetailCommandHandler(
 {
     public async Task<Guid> Handle(AddPurchaseEvaluationDetailCommand request, CancellationToken ct)
     {
-        var evaluation = await PurchaseEvaluationDraftGuard.EnsureDraftAsync(db, request.PurchaseEvaluationId, ct);
+        var evaluation = await PurchaseEvaluationDraftGuard.EnsureEditableForDetailsAsync(
+            db, request.PurchaseEvaluationId, currentUser, ct);
 
         var maxOrder = await db.PurchaseEvaluationDetails
             .Where(d => d.PurchaseEvaluationId == request.PurchaseEvaluationId)
@@ -110,11 +184,13 @@ public record UpdatePurchaseEvaluationDetailCommand(
     string? GhiChu) : IRequest;
 
 public class UpdatePurchaseEvaluationDetailCommandHandler(
-    IApplicationDbContext db) : IRequestHandler<UpdatePurchaseEvaluationDetailCommand>
+    IApplicationDbContext db,
+    ICurrentUser currentUser) : IRequestHandler<UpdatePurchaseEvaluationDetailCommand>
 {
     public async Task Handle(UpdatePurchaseEvaluationDetailCommand request, CancellationToken ct)
     {
-        await PurchaseEvaluationDraftGuard.EnsureDraftAsync(db, request.PurchaseEvaluationId, ct);
+        var evaluation = await PurchaseEvaluationDraftGuard.EnsureEditableForDetailsAsync(
+            db, request.PurchaseEvaluationId, currentUser, ct);
         var entity = await db.PurchaseEvaluationDetails
             .FirstOrDefaultAsync(x => x.Id == request.DetailId && x.PurchaseEvaluationId == request.PurchaseEvaluationId, ct)
             ?? throw new NotFoundException("PurchaseEvaluationDetail", request.DetailId);
@@ -130,6 +206,21 @@ public class UpdatePurchaseEvaluationDetailCommandHandler(
         entity.ThanhTienNganSach = request.ThanhTienNganSach;
         entity.GhiChu = request.GhiChu;
 
+        // F3 audit (Mig 28) — log Approver edit Section 2. Drafter edit cũng log
+        // để audit trail consistent. Phase ChoDuyet → flag "Approver" trong summary.
+        var approverNote = evaluation.Phase == PurchaseEvaluationPhase.ChoDuyet
+            ? " [Approver edit khi đang duyệt]" : string.Empty;
+        db.PurchaseEvaluationChangelogs.Add(new PurchaseEvaluationChangelog
+        {
+            PurchaseEvaluationId = request.PurchaseEvaluationId,
+            EntityType = PurchaseEvaluationEntityType.Detail,
+            EntityId = entity.Id,
+            Action = ChangelogAction.Update,
+            PhaseAtChange = evaluation.Phase,
+            UserId = currentUser.UserId,
+            Summary = $"Cập nhật hạng mục {request.GroupCode} — {request.NoiDung}{approverNote}",
+        });
+
         await db.SaveChangesAsync(ct);
     }
 }
@@ -137,15 +228,30 @@ public class UpdatePurchaseEvaluationDetailCommandHandler(
 public record DeletePurchaseEvaluationDetailCommand(Guid PurchaseEvaluationId, Guid DetailId) : IRequest;
 
 public class DeletePurchaseEvaluationDetailCommandHandler(
-    IApplicationDbContext db) : IRequestHandler<DeletePurchaseEvaluationDetailCommand>
+    IApplicationDbContext db,
+    ICurrentUser currentUser) : IRequestHandler<DeletePurchaseEvaluationDetailCommand>
 {
     public async Task Handle(DeletePurchaseEvaluationDetailCommand request, CancellationToken ct)
     {
-        await PurchaseEvaluationDraftGuard.EnsureDraftAsync(db, request.PurchaseEvaluationId, ct);
+        var evaluation = await PurchaseEvaluationDraftGuard.EnsureEditableForDetailsAsync(
+            db, request.PurchaseEvaluationId, currentUser, ct);
         var entity = await db.PurchaseEvaluationDetails
             .FirstOrDefaultAsync(x => x.Id == request.DetailId && x.PurchaseEvaluationId == request.PurchaseEvaluationId, ct)
             ?? throw new NotFoundException("PurchaseEvaluationDetail", request.DetailId);
 
+        var approverNote = evaluation.Phase == PurchaseEvaluationPhase.ChoDuyet
+            ? " [Approver edit khi đang duyệt]" : string.Empty;
+        db.PurchaseEvaluationChangelogs.Add(new PurchaseEvaluationChangelog
+        {
+            PurchaseEvaluationId = request.PurchaseEvaluationId,
+            EntityType = PurchaseEvaluationEntityType.Detail,
+            EntityId = entity.Id,
+            Action = ChangelogAction.Delete,
+            PhaseAtChange = evaluation.Phase,
+            UserId = currentUser.UserId,
+            Summary = $"Xóa hạng mục {entity.GroupCode} — {entity.NoiDung}{approverNote}",
+        });
+
         db.PurchaseEvaluationDetails.Remove(entity);
         await db.SaveChangesAsync(ct);
     }
@@ -164,11 +270,13 @@ public record UpsertPurchaseEvaluationQuoteCommand(
     string? Note) : IRequest<Guid>;
 
 public class UpsertPurchaseEvaluationQuoteCommandHandler(
-    IApplicationDbContext db) : IRequestHandler<UpsertPurchaseEvaluationQuoteCommand, Guid>
+    IApplicationDbContext db,
+    ICurrentUser currentUser) : IRequestHandler<UpsertPurchaseEvaluationQuoteCommand, Guid>
 {
     public async Task<Guid> Handle(UpsertPurchaseEvaluationQuoteCommand request, CancellationToken ct)
     {
-        await PurchaseEvaluationDraftGuard.EnsureDraftAsync(db, request.PurchaseEvaluationId, ct);
+        var evaluation = await PurchaseEvaluationDraftGuard.EnsureEditableForDetailsAsync(
+            db, request.PurchaseEvaluationId, currentUser, ct);
         // Verify parents exist + same phiếu
         var detail = await db.PurchaseEvaluationDetails.FirstOrDefaultAsync(
             d => d.Id == request.PurchaseEvaluationDetailId && d.PurchaseEvaluationId == request.PurchaseEvaluationId, ct)
@@ -182,6 +290,9 @@ public class UpsertPurchaseEvaluationQuoteCommandHandler(
             q => q.PurchaseEvaluationDetailId == request.PurchaseEvaluationDetailId
                 && q.PurchaseEvaluationSupplierId == request.PurchaseEvaluationSupplierId, ct);
 
+        var approverNote = evaluation.Phase == PurchaseEvaluationPhase.ChoDuyet
+            ? " [Approver edit khi đang duyệt]" : string.Empty;
+
         if (existing is not null)
         {
             existing.BgVat = request.BgVat;
@@ -189,6 +300,16 @@ public class UpsertPurchaseEvaluationQuoteCommandHandler(
             existing.ThanhTien = request.ThanhTien;
             existing.IsSelected = request.IsSelected;
             existing.Note = request.Note;
+            db.PurchaseEvaluationChangelogs.Add(new PurchaseEvaluationChangelog
+            {
+                PurchaseEvaluationId = request.PurchaseEvaluationId,
+                EntityType = PurchaseEvaluationEntityType.Quote,
+                EntityId = existing.Id,
+                Action = ChangelogAction.Update,
+                PhaseAtChange = evaluation.Phase,
+                UserId = currentUser.UserId,
+                Summary = $"Cập nhật báo giá cho hạng mục {detail.GroupCode}{approverNote}",
+            });
             await db.SaveChangesAsync(ct);
             return existing.Id;
         }
@@ -204,6 +325,16 @@ public class UpsertPurchaseEvaluationQuoteCommandHandler(
             Note = request.Note,
         };
         db.PurchaseEvaluationQuotes.Add(entity);
+        db.PurchaseEvaluationChangelogs.Add(new PurchaseEvaluationChangelog
+        {
+            PurchaseEvaluationId = request.PurchaseEvaluationId,
+            EntityType = PurchaseEvaluationEntityType.Quote,
+            EntityId = entity.Id,
+            Action = ChangelogAction.Insert,
+            PhaseAtChange = evaluation.Phase,
+            UserId = currentUser.UserId,
+            Summary = $"Thêm báo giá cho hạng mục {detail.GroupCode}{approverNote}",
+        });
         await db.SaveChangesAsync(ct);
         return entity.Id;
     }
@@ -212,11 +343,13 @@ public class UpsertPurchaseEvaluationQuoteCommandHandler(
 public record DeletePurchaseEvaluationQuoteCommand(Guid PurchaseEvaluationId, Guid QuoteId) : IRequest;
 
 public class DeletePurchaseEvaluationQuoteCommandHandler(
-    IApplicationDbContext db) : IRequestHandler<DeletePurchaseEvaluationQuoteCommand>
+    IApplicationDbContext db,
+    ICurrentUser currentUser) : IRequestHandler<DeletePurchaseEvaluationQuoteCommand>
 {
     public async Task Handle(DeletePurchaseEvaluationQuoteCommand request, CancellationToken ct)
     {
-        await PurchaseEvaluationDraftGuard.EnsureDraftAsync(db, request.PurchaseEvaluationId, ct);
+        var evaluation = await PurchaseEvaluationDraftGuard.EnsureEditableForDetailsAsync(
+            db, request.PurchaseEvaluationId, currentUser, ct);
         var quote = await (
             from q in db.PurchaseEvaluationQuotes
             join d in db.PurchaseEvaluationDetails on q.PurchaseEvaluationDetailId equals d.Id
@@ -224,6 +357,19 @@ public class DeletePurchaseEvaluationQuoteCommandHandler(
             select q).FirstOrDefaultAsync(ct)
             ?? throw new NotFoundException("PurchaseEvaluationQuote", request.QuoteId);
 
+        var approverNote = evaluation.Phase == PurchaseEvaluationPhase.ChoDuyet
+            ? " [Approver edit khi đang duyệt]" : string.Empty;
+        db.PurchaseEvaluationChangelogs.Add(new PurchaseEvaluationChangelog
+        {
+            PurchaseEvaluationId = request.PurchaseEvaluationId,
+            EntityType = PurchaseEvaluationEntityType.Quote,
+            EntityId = quote.Id,
+            Action = ChangelogAction.Delete,
+            PhaseAtChange = evaluation.Phase,
+            UserId = currentUser.UserId,
+            Summary = $"Xóa báo giá{approverNote}",
+        });
+
         db.PurchaseEvaluationQuotes.Remove(quote);
         await db.SaveChangesAsync(ct);
     }

src/Backend/SolutionErp.Application/PurchaseEvaluations/PurchaseEvaluationFeatures.cs

@@ -244,7 +244,12 @@ public record TransitionPurchaseEvaluationCommand(
     Guid Id,
     PurchaseEvaluationPhase TargetPhase,
     ApprovalDecision Decision,
-    string? Comment) : IRequest;
+    string? Comment,
+    // Mig 28 (S21 t4) — F1 mode Trả lại (optional, null = default Drafter)
+    WorkflowReturnMode? ReturnMode = null,
+    Guid? ReturnTargetUserId = null,
+    // F2 — Drafter skip thẳng Cấp cuối khi trình duyệt (optional, default false)
+    bool SkipToFinal = false) : IRequest;
 
 public class TransitionPurchaseEvaluationCommandValidator : AbstractValidator<TransitionPurchaseEvaluationCommand>
 {
@@ -254,6 +259,11 @@ public class TransitionPurchaseEvaluationCommandValidator : AbstractValidator<Tr
         RuleFor(x => x.TargetPhase).IsInEnum();
         RuleFor(x => x.Decision).IsInEnum();
         RuleFor(x => x.Comment).MaximumLength(1000);
+        RuleFor(x => x.ReturnMode!.Value).IsInEnum().When(x => x.ReturnMode.HasValue);
+        // Assignee mode → returnTargetUserId required
+        RuleFor(x => x.ReturnTargetUserId).NotEmpty()
+            .When(x => x.ReturnMode == WorkflowReturnMode.Assignee)
+            .WithMessage("ReturnTargetUserId yêu cầu khi mode=Assignee.");
     }
 }
 
@@ -277,6 +287,9 @@ public class TransitionPurchaseEvaluationCommandHandler(
             currentUser.Roles,
             request.Decision,
             request.Comment,
+            request.ReturnMode,
+            request.ReturnTargetUserId,
+            request.SkipToFinal,
             ct);
     }
 }
@@ -549,6 +562,7 @@ public class GetPurchaseEvaluationQueryHandler(
         // Bước/Cấp tree với Status) cho FE render flow vertical thay phase cards.
         string? awCode = null, awName = null;
         int? awVersion = null;
+        ApprovalWorkflowOptionsDto? awOptions = null;
         PurchaseEvaluationCurrentApprovalDto? currentApproval = null;
         PurchaseEvaluationApprovalFlowDto? approvalFlow = null;
         if (e.ApprovalWorkflowId is Guid awId)
@@ -562,6 +576,14 @@ public class GetPurchaseEvaluationQueryHandler(
                 awCode = aw.Code;
                 awName = aw.Name;
                 awVersion = aw.Version;
+                // Mig 28 — 6 Allow* options pin lúc PE create
+                awOptions = new ApprovalWorkflowOptionsDto(
+                    aw.AllowReturnOneLevel,
+                    aw.AllowReturnOneStep,
+                    aw.AllowReturnToAssignee,
+                    aw.AllowReturnToDrafter,
+                    aw.AllowDrafterSkipToFinal,
+                    aw.AllowApproverEditDetails);
 
                 var steps = aw.Steps.OrderBy(s => s.Order).ToList();
                 // Resolve dept names cho Steps
@@ -681,7 +703,7 @@ public class GetPurchaseEvaluationQueryHandler(
             e.PaymentTerms, e.SlaDeadline, e.CreatedAt, e.UpdatedAt,
             e.BudgetId, budgetSummary,
             e.BudgetManualName, e.BudgetManualAmount,
-            e.ApprovalWorkflowId, awCode, awName, awVersion,
+            e.ApprovalWorkflowId, awCode, awName, awVersion, awOptions,
             currentApproval, approvalFlow,
             e.Suppliers
                 .OrderBy(s => s.Order)

src/Backend/SolutionErp.Application/PurchaseEvaluations/PurchaseEvaluationSupplierFeatures.cs

@@ -41,8 +41,10 @@ public class AddPurchaseEvaluationSupplierCommandHandler(
 {
     public async Task<Guid> Handle(AddPurchaseEvaluationSupplierCommand request, CancellationToken ct)
     {
-        var evaluation = await db.PurchaseEvaluations.FirstOrDefaultAsync(x => x.Id == request.PurchaseEvaluationId, ct)
+        // Mig 28 (S21 t4 F3) — Section 2 edit guard: Drafter (DangSoanThao/TraLai)
-            ?? throw new NotFoundException("PurchaseEvaluation", request.PurchaseEvaluationId);
+        // OR Approver (ChoDuyet + workflow.AllowApproverEditDetails + actor match).
+        var evaluation = await PurchaseEvaluationDraftGuard.EnsureEditableForDetailsAsync(
+            db, request.PurchaseEvaluationId, currentUser, ct);
 
         _ = await db.Suppliers.FirstOrDefaultAsync(s => s.Id == request.SupplierId, ct)
             ?? throw new NotFoundException("Supplier", request.SupplierId);
@@ -97,10 +99,14 @@ public record UpdatePurchaseEvaluationSupplierCommand(
     string? Note) : IRequest;
 
 public class UpdatePurchaseEvaluationSupplierCommandHandler(
-    IApplicationDbContext db) : IRequestHandler<UpdatePurchaseEvaluationSupplierCommand>
+    IApplicationDbContext db,
+    ICurrentUser currentUser) : IRequestHandler<UpdatePurchaseEvaluationSupplierCommand>
 {
     public async Task Handle(UpdatePurchaseEvaluationSupplierCommand request, CancellationToken ct)
     {
+        // Mig 28 (S21 t4 F3) — Section 2 edit guard.
+        var evaluation = await PurchaseEvaluationDraftGuard.EnsureEditableForDetailsAsync(
+            db, request.PurchaseEvaluationId, currentUser, ct);
         var row = await db.PurchaseEvaluationSuppliers
             .FirstOrDefaultAsync(s => s.Id == request.SupplierRowId && s.PurchaseEvaluationId == request.PurchaseEvaluationId, ct)
             ?? throw new NotFoundException("PurchaseEvaluationSupplier", request.SupplierRowId);
@@ -112,6 +118,19 @@ public class UpdatePurchaseEvaluationSupplierCommandHandler(
         row.PaymentTermText = request.PaymentTermText;
         row.Note = request.Note;
 
+        var approverNote = evaluation.Phase == PurchaseEvaluationPhase.ChoDuyet
+            ? " [Approver edit khi đang duyệt]" : string.Empty;
+        db.PurchaseEvaluationChangelogs.Add(new PurchaseEvaluationChangelog
+        {
+            PurchaseEvaluationId = request.PurchaseEvaluationId,
+            EntityType = PurchaseEvaluationEntityType.Supplier,
+            EntityId = row.Id,
+            Action = ChangelogAction.Update,
+            PhaseAtChange = evaluation.Phase,
+            UserId = currentUser.UserId,
+            Summary = $"Cập nhật NCC {request.DisplayName ?? "#" + row.SupplierId.ToString()[..8]}{approverNote}",
+        });
+
         await db.SaveChangesAsync(ct);
     }
 }
@@ -119,10 +138,14 @@ public class UpdatePurchaseEvaluationSupplierCommandHandler(
 public record RemovePurchaseEvaluationSupplierCommand(Guid PurchaseEvaluationId, Guid SupplierRowId) : IRequest;
 
 public class RemovePurchaseEvaluationSupplierCommandHandler(
-    IApplicationDbContext db) : IRequestHandler<RemovePurchaseEvaluationSupplierCommand>
+    IApplicationDbContext db,
+    ICurrentUser currentUser) : IRequestHandler<RemovePurchaseEvaluationSupplierCommand>
 {
     public async Task Handle(RemovePurchaseEvaluationSupplierCommand request, CancellationToken ct)
     {
+        // Mig 28 (S21 t4 F3) — Section 2 edit guard.
+        var evaluation = await PurchaseEvaluationDraftGuard.EnsureEditableForDetailsAsync(
+            db, request.PurchaseEvaluationId, currentUser, ct);
         var row = await db.PurchaseEvaluationSuppliers
             .FirstOrDefaultAsync(s => s.Id == request.SupplierRowId && s.PurchaseEvaluationId == request.PurchaseEvaluationId, ct)
             ?? throw new NotFoundException("PurchaseEvaluationSupplier", request.SupplierRowId);
@@ -131,6 +154,19 @@ public class RemovePurchaseEvaluationSupplierCommandHandler(
         var hasQuotes = await db.PurchaseEvaluationQuotes.AnyAsync(q => q.PurchaseEvaluationSupplierId == row.Id, ct);
         if (hasQuotes) throw new ConflictException("Không thể xóa NCC khi còn báo giá. Xóa báo giá trước.");
 
+        var approverNote = evaluation.Phase == PurchaseEvaluationPhase.ChoDuyet
+            ? " [Approver edit khi đang duyệt]" : string.Empty;
+        db.PurchaseEvaluationChangelogs.Add(new PurchaseEvaluationChangelog
+        {
+            PurchaseEvaluationId = request.PurchaseEvaluationId,
+            EntityType = PurchaseEvaluationEntityType.Supplier,
+            EntityId = row.Id,
+            Action = ChangelogAction.Delete,
+            PhaseAtChange = evaluation.Phase,
+            UserId = currentUser.UserId,
+            Summary = $"Xóa NCC {row.DisplayName ?? "#" + row.SupplierId.ToString()[..8]}{approverNote}",
+        });
+
         db.PurchaseEvaluationSuppliers.Remove(row);
         await db.SaveChangesAsync(ct);
     }

src/Backend/SolutionErp.Application/PurchaseEvaluations/Services/IPurchaseEvaluationWorkflowService.cs

@@ -7,6 +7,14 @@ public interface IPurchaseEvaluationWorkflowService
 {
     // Kiểm tra + thực hiện transition. Throw ForbiddenException nếu không hợp lệ.
     // Tự tạo PurchaseEvaluationApproval + update Phase + SlaDeadline.
+    //
+    // Optional params Mig 28 (S21 t4 — F1+F2 advanced workflow options):
+    // - returnMode: mode Trả lại (F1). Null = default Drafter behavior khi Reject+TraLai.
+    //   OneLevel/OneStep/Assignee → giữ Phase=ChoDuyet, lùi pointer (peer review).
+    //   Drafter → Phase=TraLai clear pointer như S17.
+    // - returnTargetUserId: required khi returnMode=Assignee — pick từ list NV đã duyệt.
+    // - skipToFinal: F2 Drafter trình duyệt → skip mọi Bước/Cấp trung gian, set pointer
+    //   = max Step + max Level. Workflow phải AllowDrafterSkipToFinal=true.
     Task TransitionAsync(
         PurchaseEvaluation evaluation,
         PurchaseEvaluationPhase targetPhase,
@@ -14,11 +22,23 @@ public interface IPurchaseEvaluationWorkflowService
         IReadOnlyList<string> actorRoles,
         ApprovalDecision decision,
         string? comment,
+        WorkflowReturnMode? returnMode = null,
+        Guid? returnTargetUserId = null,
+        bool skipToFinal = false,
         CancellationToken ct = default);
 
     TimeSpan? GetPhaseSla(PurchaseEvaluationPhase phase);
 }
 
+/// Mig 28 (S21 t4) — F1 mode Trả lại. Mapping với ApprovalWorkflow.Allow* flag.
+public enum WorkflowReturnMode
+{
+    OneLevel = 1,        // Lùi 1 Cấp trong cùng Step (peer review)
+    OneStep = 2,         // Lùi sang Bước trước, level = max của bước đó
+    Assignee = 3,        // Pick runtime từ list NV đã duyệt
+    Drafter = 4,         // Trả về Drafter, Phase=TraLai clear pointer (S17 default fallback)
+}
+
 // Atomic sequence generator cho mã PE (MaPhieu) — mirror IContractCodeGenerator.
 // Format: PE/{YYYY}/{TypeLetter}/{Seq:D3}
 //   - YYYY = năm hiện tại (UTC)

src/Backend/SolutionErp.Domain/ApprovalWorkflowsV2/ApprovalWorkflow.cs

@@ -34,6 +34,46 @@ public class ApprovalWorkflow : BaseEntity
     // khi tạo version mới (mirror IsActive default), admin có thể unstick.
     public bool IsUserSelectable { get; set; }
 
+    // ===== Mig 28 (Session 21 turn 4) — 6 advanced options per workflow =====
+    // Cấu hình "Cấu hình nâng cao" trong Admin Designer. User eOffice render
+    // dropdown/checkbox theo flag enabled. 4 flag Return* = mode Trả lại (F1).
+    // 1 flag Skip = Drafter trình thẳng Cấp cuối (F2). 1 flag EditDetails =
+    // Approver chỉnh Section 2 (F3).
+    //
+    // Default backward compat S17: AllowReturnToDrafter=true (mọi workflow cũ
+    // chạy đúng — fallback "Trả về Drafter" như Session 17 spec). 5 flag còn
+    // lại default false — admin opt-in per workflow để audit nghiêm.
+
+    /// F1 mode 1 — Cho phép Approver Trả lại 1 Cấp trước (lùi pointer trong
+    /// cùng Step). Phiếu GIỮ Phase=ChoDuyet (peer review chain).
+    public bool AllowReturnOneLevel { get; set; }
+
+    /// F1 mode 2 — Cho phép Approver Trả lại 1 Bước trước (lùi sang Step trước,
+    /// set level = max của step đó). Phiếu GIỮ Phase=ChoDuyet.
+    public bool AllowReturnOneStep { get; set; }
+
+    /// F1 mode 3 — Cho phép Approver Trả lại Người chỉ định (pick runtime từ
+    /// list NV ĐÃ DUYỆT trong PeLevelOpinions). Phiếu GIỮ Phase=ChoDuyet, set
+    /// Step/Level = vị trí của user pick trong workflow.
+    public bool AllowReturnToAssignee { get; set; }
+
+    /// F1 mode 4 — Cho phép Approver Trả lại Người soạn thảo (Drafter). Phiếu
+    /// đi vào Phase=TraLai, clear pointer (như Session 17 spec). Default TRUE
+    /// để backward compat — admin có thể unstick force peer review only.
+    public bool AllowReturnToDrafter { get; set; } = true;
+
+    /// F2 — Cho phép Drafter gửi thẳng Cấp cuối (skip mọi Bước/Cấp trung gian).
+    /// UI eOffice trình duyệt thêm dropdown 2 option ("Gửi tuần tự" default vs
+    /// "Gửi thẳng Cấp cuối"). BE set CurrentWorkflowStepIndex=maxStep,
+    /// CurrentApprovalLevelOrder=maxLevel. Audit changelog "Drafter skip C1..N".
+    public bool AllowDrafterSkipToFinal { get; set; }
+
+    /// F3 — Cho phép Approver chỉnh sửa Section 2 (Hạng mục + NCC + Báo giá)
+    /// khi phase=ChoDuyet + actor match CurrentLevel.ApproverUserId. KHÔNG đụng
+    /// PE Header (TenGoiThau/Project/Budget). KHÔNG reset workflow. Audit ghi
+    /// PurchaseEvaluationChangelog cho mỗi field/row thay đổi.
+    public bool AllowApproverEditDetails { get; set; }
+
     public List<ApprovalWorkflowStep> Steps { get; set; } = new();
 }
 

src/Backend/SolutionErp.Infrastructure/Persistence/Configurations/ApprovalWorkflowConfiguration.cs

@@ -18,6 +18,15 @@ public class ApprovalWorkflowConfiguration : IEntityTypeConfiguration<ApprovalWo
 
         e.HasIndex(x => new { x.Code, x.Version }).IsUnique();
         e.HasIndex(x => new { x.ApplicableType, x.IsActive });
+
+        // Mig 28 — 6 advanced options. 5 default false (admin opt-in). 1
+        // AllowReturnToDrafter default true (backward compat S17 fallback).
+        e.Property(x => x.AllowReturnOneLevel).HasDefaultValue(false);
+        e.Property(x => x.AllowReturnOneStep).HasDefaultValue(false);
+        e.Property(x => x.AllowReturnToAssignee).HasDefaultValue(false);
+        e.Property(x => x.AllowReturnToDrafter).HasDefaultValue(true);
+        e.Property(x => x.AllowDrafterSkipToFinal).HasDefaultValue(false);
+        e.Property(x => x.AllowApproverEditDetails).HasDefaultValue(false);
     }
 }
 

src/Backend/SolutionErp.Infrastructure/Persistence/Migrations/20260513114505_AddAdvancedOptionsToApprovalWorkflows.cs

@@ -0,0 +1,84 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace SolutionErp.Infrastructure.Persistence.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddAdvancedOptionsToApprovalWorkflows : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<bool>(
+                name: "AllowApproverEditDetails",
+                table: "ApprovalWorkflows",
+                type: "bit",
+                nullable: false,
+                defaultValue: false);
+
+            migrationBuilder.AddColumn<bool>(
+                name: "AllowDrafterSkipToFinal",
+                table: "ApprovalWorkflows",
+                type: "bit",
+                nullable: false,
+                defaultValue: false);
+
+            migrationBuilder.AddColumn<bool>(
+                name: "AllowReturnOneLevel",
+                table: "ApprovalWorkflows",
+                type: "bit",
+                nullable: false,
+                defaultValue: false);
+
+            migrationBuilder.AddColumn<bool>(
+                name: "AllowReturnOneStep",
+                table: "ApprovalWorkflows",
+                type: "bit",
+                nullable: false,
+                defaultValue: false);
+
+            migrationBuilder.AddColumn<bool>(
+                name: "AllowReturnToAssignee",
+                table: "ApprovalWorkflows",
+                type: "bit",
+                nullable: false,
+                defaultValue: false);
+
+            migrationBuilder.AddColumn<bool>(
+                name: "AllowReturnToDrafter",
+                table: "ApprovalWorkflows",
+                type: "bit",
+                nullable: false,
+                defaultValue: true);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "AllowApproverEditDetails",
+                table: "ApprovalWorkflows");
+
+            migrationBuilder.DropColumn(
+                name: "AllowDrafterSkipToFinal",
+                table: "ApprovalWorkflows");
+
+            migrationBuilder.DropColumn(
+                name: "AllowReturnOneLevel",
+                table: "ApprovalWorkflows");
+
+            migrationBuilder.DropColumn(
+                name: "AllowReturnOneStep",
+                table: "ApprovalWorkflows");
+
+            migrationBuilder.DropColumn(
+                name: "AllowReturnToAssignee",
+                table: "ApprovalWorkflows");
+
+            migrationBuilder.DropColumn(
+                name: "AllowReturnToDrafter",
+                table: "ApprovalWorkflows");
+        }
+    }
+}

src/Backend/SolutionErp.Infrastructure/Persistence/Migrations/ApplicationDbContextModelSnapshot.cs

@@ -134,6 +134,36 @@ namespace SolutionErp.Infrastructure.Persistence.Migrations
                     b.Property<DateTime?>("ActivatedAt")
                         .HasColumnType("datetime2");
 
+                    b.Property<bool>("AllowApproverEditDetails")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("bit")
+                        .HasDefaultValue(false);
+
+                    b.Property<bool>("AllowDrafterSkipToFinal")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("bit")
+                        .HasDefaultValue(false);
+
+                    b.Property<bool>("AllowReturnOneLevel")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("bit")
+                        .HasDefaultValue(false);
+
+                    b.Property<bool>("AllowReturnOneStep")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("bit")
+                        .HasDefaultValue(false);
+
+                    b.Property<bool>("AllowReturnToAssignee")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("bit")
+                        .HasDefaultValue(false);
+
+                    b.Property<bool>("AllowReturnToDrafter")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("bit")
+                        .HasDefaultValue(true);
+
                     b.Property<int>("ApplicableType")
                         .HasColumnType("int");
 

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

@@ -41,29 +41,55 @@ public class PurchaseEvaluationWorkflowService(
         IReadOnlyList<string> actorRoles,
         ApprovalDecision decision,
         string? comment,
+        WorkflowReturnMode? returnMode = null,
+        Guid? returnTargetUserId = null,
+        bool skipToFinal = false,
         CancellationToken ct = default)
     {
         var fromPhase = evaluation.Phase;
         var isAdmin = actorRoles.Contains(AppRoles.Admin);
         var isSystem = actorUserId is null && decision == ApprovalDecision.AutoApprove;
 
-        // ===== REJECT BRANCH =====
+        // ===== GUARD: targetPhase TraLai/TuChoi BẮT BUỘC decision=Reject =====
+        // Defense-in-depth chặn FE inconsistency (gotcha #45 — Session 21 turn 3):
+        //   Bug: button "← Trả lại" trong PeWorkflowPanel.tsx gửi decision=Approve
+        //   khi target=TraLai do `isReject` local var thiếu nhánh TraLai. BE nhận
+        //   payload sẽ skip Reject branch → enter APPROVE STEP → ApproveV2Async
+        //   UPSERT opinion = "đã duyệt" + advance Cấp. User UAT thấy: "Trả về
+        //   nhưng hệ thống vẫn duyệt".
+        // FE fix song song trong fe-admin + fe-user (rule §3.9 mirror 2 app).
+        // Guard này KHÔNG xoá khi FE fix — boundary protection cho mọi caller
+        // tương lai (API client / mobile app / cron retry).
+        if ((targetPhase == PurchaseEvaluationPhase.TraLai
+                || targetPhase == PurchaseEvaluationPhase.TuChoi)
+            && decision != ApprovalDecision.Reject)
+        {
+            throw new ConflictException(
+                $"Transition tới {targetPhase} BẮT BUỘC decision=Reject (nhận {decision}). " +
+                "Báo lỗi caller — payload mismatch giữa target phase và decision " +
+                "(xem gotcha #45 + docs/workflow-contract.md).");
+        }
+
+        // ===== REJECT BRANCH (extended Mig 28 — F1 multi-mode Trả lại) =====
         if (decision == ApprovalDecision.Reject)
         {
             if (targetPhase == PurchaseEvaluationPhase.TuChoi)
             {
                 // Từ chối hoàn toàn — phiếu khoá vĩnh viễn (lock edit Mig 16).
                 evaluation.Phase = PurchaseEvaluationPhase.TuChoi;
+                evaluation.SlaDeadline = null;
             }
             else
             {
-                // Trả lại — Phase=TraLai RIÊNG (không revert về DangSoanThao).
+                // F1 (S21 t4) — 4 mode Trả lại theo workflow.Allow* flag.
-                // Drafter sửa từ TraLai rồi gửi lại sẽ chạy lại từ Cấp 1 Bước 1.
+                // Default fallback (returnMode=null) = Drafter mode = S17 behavior.
-                evaluation.Phase = PurchaseEvaluationPhase.TraLai;
+                var effectiveMode = returnMode ?? WorkflowReturnMode.Drafter;
-                evaluation.CurrentWorkflowStepIndex = null;
+                var returnSummary = await ApplyReturnModeAsync(
-                evaluation.CurrentApprovalLevelOrder = null;
+                    evaluation, effectiveMode, returnTargetUserId, isAdmin, ct);
+                comment = string.IsNullOrWhiteSpace(comment)
+                    ? returnSummary
+                    : $"{comment} [{returnSummary}]";
             }
-            evaluation.SlaDeadline = null;
             await LogTransitionAsync(evaluation, fromPhase, evaluation.Phase, actorUserId, decision, comment, ct);
             await db.SaveChangesAsync(ct);
             return;
@@ -84,9 +110,36 @@ public class PurchaseEvaluationWorkflowService(
                     $"Role ({string.Join(",", actorRoles)}) không đủ quyền trình duyệt phiếu.");
             }
             evaluation.Phase = PurchaseEvaluationPhase.ChoDuyet;
+
+            // F2 (Mig 28 — S21 t4) — Drafter skip thẳng Cấp cuối. Workflow phải
+            // AllowDrafterSkipToFinal=true. Set pointer = max Step + max Level.
+            // Audit changelog ghi rõ "Drafter skip" để approver Cấp cuối biết.
+            if (skipToFinal && evaluation.ApprovalWorkflowId is Guid skipAwId)
+            {
+                var wfSkip = await db.ApprovalWorkflows
+                    .Include(w => w.Steps).ThenInclude(s => s.Levels)
+                    .FirstOrDefaultAsync(w => w.Id == skipAwId, ct)
+                    ?? throw new ConflictException("Workflow không tồn tại.");
+                if (!wfSkip.AllowDrafterSkipToFinal)
+                    throw new ConflictException(
+                        "Workflow không bật mode 'Gửi thẳng Cấp cuối'. " +
+                        "Liên hệ Admin để config Designer.");
+                var finalStep = wfSkip.Steps.OrderBy(s => s.Order).LastOrDefault()
+                    ?? throw new ConflictException("Workflow chưa có Bước nào.");
+                var finalLevelOrder = finalStep.Levels.OrderBy(l => l.Order).LastOrDefault()?.Order
+                    ?? throw new ConflictException($"Bước {finalStep.Order} chưa có Cấp nào.");
+                evaluation.CurrentWorkflowStepIndex = wfSkip.Steps.Count - 1;  // 0-based last step
+                evaluation.CurrentApprovalLevelOrder = finalLevelOrder;
+                comment = string.IsNullOrWhiteSpace(comment)
+                    ? "[Drafter gửi thẳng Cấp cuối — skip Bước/Cấp trung gian]"
+                    : $"{comment} [Drafter gửi thẳng Cấp cuối — skip Bước/Cấp trung gian]";
+            }
+            else
+            {
                 evaluation.CurrentWorkflowStepIndex = 0;
                 // Chỉ init levelOrder=1 nếu pin schema V2 (ApprovalWorkflowId set).
                 evaluation.CurrentApprovalLevelOrder = evaluation.ApprovalWorkflowId is not null ? 1 : null;
+            }
             evaluation.SlaDeadline = dateTime.UtcNow.AddDays(7);
             await LogTransitionAsync(evaluation, fromPhase, PurchaseEvaluationPhase.ChoDuyet, actorUserId, decision, comment, ct);
             await db.SaveChangesAsync(ct);
@@ -124,6 +177,154 @@ public class PurchaseEvaluationWorkflowService(
         throw new ConflictException($"Transition {fromPhase} → {targetPhase} không hỗ trợ.");
     }
 
+    // ===== F1 (Mig 28 — S21 t4) — Apply Return Mode =====
+    // Switch theo effectiveMode → set Phase + pointer. 3 mode đầu giữ ChoDuyet
+    // (peer review chain). Mode Drafter set Phase=TraLai như S17.
+    // Validate workflow.Allow* flag match mode → throw nếu disabled.
+    // Return summary text để chèn vào comment changelog (audit trail).
+    private async Task<string> ApplyReturnModeAsync(
+        PurchaseEvaluation evaluation,
+        WorkflowReturnMode mode,
+        Guid? returnTargetUserId,
+        bool isAdmin,
+        CancellationToken ct)
+    {
+        // Mode Drafter — Session 17 default (always allowed for backward compat,
+        // workflow.AllowReturnToDrafter default true).
+        if (mode == WorkflowReturnMode.Drafter)
+        {
+            // Validate workflow flag (admin có thể disable mode này force peer review)
+            if (evaluation.ApprovalWorkflowId is Guid awId0 && !isAdmin)
+            {
+                var wf0 = await db.ApprovalWorkflows.FirstOrDefaultAsync(w => w.Id == awId0, ct);
+                if (wf0 is not null && !wf0.AllowReturnToDrafter)
+                    throw new ConflictException(
+                        "Workflow không bật mode 'Trả về Drafter'. Phải dùng mode khác.");
+            }
+            evaluation.Phase = PurchaseEvaluationPhase.TraLai;
+            evaluation.CurrentWorkflowStepIndex = null;
+            evaluation.CurrentApprovalLevelOrder = null;
+            evaluation.SlaDeadline = null;
+            return "Trả về Người soạn thảo";
+        }
+
+        // 3 mode còn lại (OneLevel / OneStep / Assignee) — yêu cầu V2 schema +
+        // pointer hợp lệ.
+        if (evaluation.ApprovalWorkflowId is not Guid awId)
+            throw new ConflictException(
+                $"Mode '{mode}' yêu cầu phiếu pin V2 workflow (ApprovalWorkflowId).");
+        if (evaluation.CurrentWorkflowStepIndex is not int curStepIdx
+            || evaluation.CurrentApprovalLevelOrder is not int curLevel)
+            throw new ConflictException(
+                $"Mode '{mode}' yêu cầu phiếu đang ChoDuyet + pointer init. " +
+                $"State hiện tại: Step={evaluation.CurrentWorkflowStepIndex}, Level={evaluation.CurrentApprovalLevelOrder}.");
+
+        var workflow = await db.ApprovalWorkflows
+            .Include(w => w.Steps).ThenInclude(s => s.Levels)
+            .FirstOrDefaultAsync(w => w.Id == awId, ct)
+            ?? throw new ConflictException("Workflow không tồn tại.");
+
+        // Validate Allow* flag (Admin bypass — admin có thể trả lại bất chấp config)
+        if (!isAdmin)
+        {
+            var allowed = mode switch
+            {
+                WorkflowReturnMode.OneLevel => workflow.AllowReturnOneLevel,
+                WorkflowReturnMode.OneStep => workflow.AllowReturnOneStep,
+                WorkflowReturnMode.Assignee => workflow.AllowReturnToAssignee,
+                _ => false,
+            };
+            if (!allowed)
+                throw new ConflictException(
+                    $"Workflow không bật mode '{mode}'. Liên hệ Admin Designer để config.");
+        }
+
+        var stepsOrdered = workflow.Steps.OrderBy(s => s.Order).ToList();
+        var summary = string.Empty;
+
+        switch (mode)
+        {
+            case WorkflowReturnMode.OneLevel:
+                // Lùi 1 Cấp trong cùng Step. Nếu đang Cấp 1 → lùi sang Bước trước
+                // Cấp cuối. Nếu đang Bước 1 Cấp 1 → fallback Drafter (no further).
+                if (curLevel > 1)
+                {
+                    evaluation.CurrentApprovalLevelOrder = curLevel - 1;
+                    summary = $"Trả về Cấp {curLevel - 1} (cùng Bước {stepsOrdered[curStepIdx].Order})";
+                }
+                else if (curStepIdx > 0)
+                {
+                    var prevStep = stepsOrdered[curStepIdx - 1];
+                    var prevMaxLevel = prevStep.Levels.OrderBy(l => l.Order).Last().Order;
+                    evaluation.CurrentWorkflowStepIndex = curStepIdx - 1;
+                    evaluation.CurrentApprovalLevelOrder = prevMaxLevel;
+                    summary = $"Trả về Bước {prevStep.Order} Cấp {prevMaxLevel} (Bước trước)";
+                }
+                else
+                {
+                    // Bước 1 Cấp 1 — no further back. Fallback Drafter.
+                    evaluation.Phase = PurchaseEvaluationPhase.TraLai;
+                    evaluation.CurrentWorkflowStepIndex = null;
+                    evaluation.CurrentApprovalLevelOrder = null;
+                    evaluation.SlaDeadline = null;
+                    return "Trả về Người soạn thảo (fallback — đang Bước 1 Cấp 1)";
+                }
+                break;
+
+            case WorkflowReturnMode.OneStep:
+                // Lùi sang Bước trước, set Level = max của Bước đó.
+                if (curStepIdx > 0)
+                {
+                    var prevStep = stepsOrdered[curStepIdx - 1];
+                    var prevMaxLevel = prevStep.Levels.OrderBy(l => l.Order).Last().Order;
+                    evaluation.CurrentWorkflowStepIndex = curStepIdx - 1;
+                    evaluation.CurrentApprovalLevelOrder = prevMaxLevel;
+                    summary = $"Trả về Bước {prevStep.Order} Cấp {prevMaxLevel}";
+                }
+                else
+                {
+                    // Đang Bước 1 → fallback Drafter
+                    evaluation.Phase = PurchaseEvaluationPhase.TraLai;
+                    evaluation.CurrentWorkflowStepIndex = null;
+                    evaluation.CurrentApprovalLevelOrder = null;
+                    evaluation.SlaDeadline = null;
+                    return "Trả về Người soạn thảo (fallback — đang Bước đầu)";
+                }
+                break;
+
+            case WorkflowReturnMode.Assignee:
+                if (returnTargetUserId is not Guid targetUid)
+                    throw new ConflictException("returnTargetUserId yêu cầu khi mode=Assignee.");
+                var foundStepIdx = -1;
+                int foundLevel = -1;
+                string? foundStepName = null;
+                for (int si = 0; si < stepsOrdered.Count; si++)
+                {
+                    var match = stepsOrdered[si].Levels
+                        .FirstOrDefault(l => l.ApproverUserId == targetUid);
+                    if (match is not null)
+                    {
+                        foundStepIdx = si;
+                        foundLevel = match.Order;
+                        foundStepName = stepsOrdered[si].Name;
+                        break;
+                    }
+                }
+                if (foundStepIdx < 0)
+                    throw new ConflictException(
+                        "Không tìm thấy người chỉ định trong workflow. " +
+                        "Chỉ pick từ list NV đã duyệt trước đó (PeLevelOpinions).");
+                evaluation.CurrentWorkflowStepIndex = foundStepIdx;
+                evaluation.CurrentApprovalLevelOrder = foundLevel;
+                summary = $"Trả về Người chỉ định — Bước {stepsOrdered[foundStepIdx].Order} ({foundStepName}) Cấp {foundLevel}";
+                break;
+        }
+
+        // 3 mode trên đều giữ Phase=ChoDuyet — reset SLA cho approver mới.
+        evaluation.SlaDeadline = dateTime.UtcNow.AddDays(7);
+        return summary;
+    }
+
     // ===== V2 schema (Mig 22-24) — iterate ApprovalWorkflowSteps + Levels =====
     private async Task ApproveV2Async(
         PurchaseEvaluation evaluation,

tests/SolutionErp.Infrastructure.Tests/Services/PurchaseEvaluationWorkflowServiceGuardTests.cs

@@ -0,0 +1,176 @@
+using Microsoft.AspNetCore.Identity;
+using Microsoft.Extensions.DependencyInjection;
+using SolutionErp.Application.Common.Exceptions;
+using SolutionErp.Application.Notifications;
+using SolutionErp.Domain.Common;
+using SolutionErp.Domain.Contracts;   // ApprovalDecision enum (shared HĐ/PE)
+using SolutionErp.Domain.Identity;
+using SolutionErp.Domain.Notifications;
+using SolutionErp.Domain.PurchaseEvaluations;
+using SolutionErp.Infrastructure.Services;
+using SolutionErp.Infrastructure.Tests.Common;
+
+namespace SolutionErp.Infrastructure.Tests.Services;
+
+// Regression test for Session 21 turn 3 bug — gotcha #45:
+// FE button "← Trả lại" trong PeWorkflowPanel gửi `decision: 1` (Approve) thay
+// vì `2` (Reject) khi target = TraLai (98). Root: `isReject` local variable
+// trong FE thiếu nhánh TraLai → payload mismatch giữa button label hiển thị
+// "Trả lại" và decision gửi BE.
+//
+// Hiệu ứng cũ trước fix: BE TransitionAsync nhận decision=Approve → skip Reject
+// branch (L51) → enter APPROVE STEP branch (L97) → ApproveV2Async UPSERT
+// opinion đánh dấu "đã duyệt" cho NV đang nhấn nút → tiến qua Cấp tiếp theo.
+// User UAT thấy: "Trả về nhưng hệ thống vẫn duyệt".
+//
+// Fix BE defense-in-depth: guard early throw ConflictException khi targetPhase
+// ∈ {TraLai, TuChoi} mà decision != Reject — chặn FE inconsistency tại
+// boundary BE thay vì depend FE đúng.
+//
+// FE fix song song trong fe-admin + fe-user PeWorkflowPanel.tsx (rule §3.9
+// mirror 2 app) — sync `isReject` + dialog `isSendBack` include TraLai.
+public class PurchaseEvaluationWorkflowServiceGuardTests
+{
+    private static (PurchaseEvaluationWorkflowService svc, IdentityFixture fix, TestApplicationDbContext db)
+        CreateService()
+    {
+        var fix = new IdentityFixture();
+        var db = fix.Services.GetRequiredService<TestApplicationDbContext>();
+        var um = fix.Services.GetRequiredService<UserManager<User>>();
+        var dt = new FixedDateTime(new DateTime(2026, 5, 12, 0, 0, 0, DateTimeKind.Utc));
+        var notify = new NoOpNotificationService();
+        var svc = new PurchaseEvaluationWorkflowService(db, dt, notify, um);
+        return (svc, fix, db);
+    }
+
+    private static PurchaseEvaluation BuildPeInChoDuyet(string code = "PE-GUARD-001")
+    {
+        return new PurchaseEvaluation
+        {
+            Id = Guid.NewGuid(),
+            Type = PurchaseEvaluationType.DuyetNcc,
+            Phase = PurchaseEvaluationPhase.ChoDuyet,
+            MaPhieu = code,
+            TenGoiThau = "Test guard bug Trả lại",
+            ProjectId = Guid.NewGuid(),
+            DrafterUserId = Guid.NewGuid(),
+            CurrentApprovalLevelOrder = 1,
+            CurrentWorkflowStepIndex = 0,
+        };
+    }
+
+    [Fact]
+    public async Task TransitionAsync_TargetTraLai_WithApproveDecision_Throws_AndDoesNotMutateState()
+    {
+        // Arrange: phiếu PE ở ChoDuyet (typical intermediate state khi approver duyệt)
+        var (svc, fix, db) = CreateService();
+        using (fix)
+        {
+            var pe = BuildPeInChoDuyet();
+            db.PurchaseEvaluations.Add(pe);
+            await db.SaveChangesAsync(CancellationToken.None);
+
+            // Act: simulate FE bug payload — button "← Trả lại" gửi decision=Approve
+            // thay vì Reject (gotcha #45 root cause).
+            var act = async () => await svc.TransitionAsync(
+                evaluation: pe,
+                targetPhase: PurchaseEvaluationPhase.TraLai,
+                actorUserId: Guid.NewGuid(),
+                actorRoles: new[] { AppRoles.CostControl },
+                decision: ApprovalDecision.Approve,
+                comment: "test guard mismatch",
+                ct: CancellationToken.None);
+
+            // Assert: BE chặn payload mismatch sớm + state phiếu KHÔNG đổi
+            await act.Should().ThrowAsync<ConflictException>()
+                .WithMessage("*TraLai*Reject*");
+
+            pe.Phase.Should().Be(PurchaseEvaluationPhase.ChoDuyet,
+                "Guard chặn trước khi mutate phase");
+            pe.CurrentApprovalLevelOrder.Should().Be(1,
+                "Guard chặn trước khi advance level pointer");
+        }
+    }
+
+    [Fact]
+    public async Task TransitionAsync_TargetTuChoi_WithApproveDecision_Throws_AndDoesNotMutateState()
+    {
+        // Tương tự TraLai — TuChoi cũng BẮT BUỘC decision=Reject. Defense
+        // double-cover invariant (FE chỉ bug TraLai branch nhưng guard nên cover
+        // luôn TuChoi cho consistency).
+        var (svc, fix, db) = CreateService();
+        using (fix)
+        {
+            var pe = BuildPeInChoDuyet("PE-GUARD-002");
+            db.PurchaseEvaluations.Add(pe);
+            await db.SaveChangesAsync(CancellationToken.None);
+
+            var act = async () => await svc.TransitionAsync(
+                evaluation: pe,
+                targetPhase: PurchaseEvaluationPhase.TuChoi,
+                actorUserId: Guid.NewGuid(),
+                actorRoles: new[] { AppRoles.CostControl },
+                decision: ApprovalDecision.Approve,
+                comment: "test guard tu choi",
+                ct: CancellationToken.None);
+
+            await act.Should().ThrowAsync<ConflictException>()
+                .WithMessage("*TuChoi*Reject*");
+
+            pe.Phase.Should().Be(PurchaseEvaluationPhase.ChoDuyet);
+        }
+    }
+
+    [Fact]
+    public async Task TransitionAsync_TargetTraLai_WithRejectDecision_SetsPhaseTraLai()
+    {
+        // Happy path control test: decision=Reject + target=TraLai → BE đi vào
+        // Reject branch (L51), set Phase=TraLai, clear pointer. Verify fix
+        // KHÔNG break flow Trả lại đúng.
+        var (svc, fix, db) = CreateService();
+        using (fix)
+        {
+            var pe = BuildPeInChoDuyet("PE-GUARD-003");
+            db.PurchaseEvaluations.Add(pe);
+            await db.SaveChangesAsync(CancellationToken.None);
+
+            await svc.TransitionAsync(
+                evaluation: pe,
+                targetPhase: PurchaseEvaluationPhase.TraLai,
+                actorUserId: Guid.NewGuid(),
+                actorRoles: new[] { AppRoles.CostControl },
+                decision: ApprovalDecision.Reject,
+                comment: "trả lại sửa lại đi",
+                ct: CancellationToken.None);
+
+            pe.Phase.Should().Be(PurchaseEvaluationPhase.TraLai,
+                "Reject branch set Phase=TraLai");
+            pe.CurrentApprovalLevelOrder.Should().BeNull("Trả lại clear level pointer");
+            pe.CurrentWorkflowStepIndex.Should().BeNull("Trả lại clear step pointer");
+            pe.SlaDeadline.Should().BeNull("Trả lại clear SLA");
+        }
+    }
+}
+
+// Stub: not assert side effects of notify (out-of-scope cho guard test).
+// Pattern reuse cho future PE service tests.
+internal sealed class NoOpNotificationService : INotificationService
+{
+    public Task NotifyAsync(
+        Guid userId,
+        NotificationType type,
+        string title,
+        string? description = null,
+        string? href = null,
+        Guid? refId = null,
+        CancellationToken ct = default) => Task.CompletedTask;
+
+    public Task NotifyManyAsync(
+        IEnumerable<Guid> userIds,
+        NotificationType type,
+        string title,
+        string? description = null,
+        string? href = null,
+        Guid? refId = null,
+        CancellationToken ct = default) => Task.CompletedTask;
+}