diff --git a/backend/src/modules/circulation/circulation-workflow.service.ts b/backend/src/modules/circulation/circulation-workflow.service.ts
index 7fe552f..475d699 100644
--- a/backend/src/modules/circulation/circulation-workflow.service.ts
+++ b/backend/src/modules/circulation/circulation-workflow.service.ts
@@ -51,7 +51,7 @@ export class CirculationWorkflowService {
       // Context — Circulation เป็น internal document ระดับ Organization (ไม่ผูก contract)
       // Guard Level 2 ตรวจ organizationId; Level 2.5 (contract check) จะ skip เมื่อ contractId = null
       const context: Record<string, unknown> = {
-        organizationId: circulation.organization,
+        organizationId: circulation.organizationId,
         creatorId: userId,
       };
 
diff --git a/backend/src/modules/circulation/circulation.service.ts b/backend/src/modules/circulation/circulation.service.ts
index 9b15505..978639a 100644
--- a/backend/src/modules/circulation/circulation.service.ts
+++ b/backend/src/modules/circulation/circulation.service.ts
@@ -325,12 +325,14 @@ export class CirculationService {
     await this.routingRepo.save(routing);
 
     // Check: ถ้าทุกคนทำเสร็จแล้ว ให้ปิดใบเวียน (Master)
-    const pendingCount = await this.routingRepo.count({
-      where: {
-        circulationId: routing.circulationId,
-        status: 'PENDING', // หรือ status ที่ยังไม่เสร็จ
-      },
-    });
+    // Bug 5 fix: นับทั้ง PENDING และ IN_PROGRESS — forceClose() ปิดทั้งสองสถานะ
+    const pendingCount = await this.routingRepo
+      .createQueryBuilder('r')
+      .where('r.circulationId = :cid', { cid: routing.circulationId })
+      .andWhere('r.status IN (:...statuses)', {
+        statuses: ['PENDING', 'IN_PROGRESS'],
+      })
+      .getCount();
 
     if (pendingCount === 0) {
       await this.circulationRepo.update(routing.circulationId, {
diff --git a/backend/src/modules/transmittal/transmittal.controller.ts b/backend/src/modules/transmittal/transmittal.controller.ts
index 01d92c7..83c86f0 100644
--- a/backend/src/modules/transmittal/transmittal.controller.ts
+++ b/backend/src/modules/transmittal/transmittal.controller.ts
@@ -1,6 +1,8 @@
 import {
+  BadRequestException,
   Controller,
   Get,
+  Headers,
   Post,
   Body,
   Param,
@@ -85,8 +87,12 @@ export class TransmittalController {
   @Audit('transmittal.submit', 'transmittal')
   submit(
     @Param('uuid', ParseUuidPipe) uuid: string,
-    @CurrentUser() user: User
+    @CurrentUser() user: User,
+    @Headers('Idempotency-Key') idempotencyKey: string
   ) {
+    if (!idempotencyKey) {
+      throw new BadRequestException('Idempotency-Key header is required');
+    }
     return this.transmittalService.submit(uuid, user);
   }
 }
diff --git a/backend/src/modules/transmittal/transmittal.service.ts b/backend/src/modules/transmittal/transmittal.service.ts
index d5dcba0..bf20985 100644
--- a/backend/src/modules/transmittal/transmittal.service.ts
+++ b/backend/src/modules/transmittal/transmittal.service.ts
@@ -252,7 +252,7 @@ export class TransmittalService {
       Correspondence,
       {
         where: { publicId: uuid },
-        select: ['id', 'correspondenceNumber', 'disciplineId'],
+        select: ['id', 'correspondenceNumber', 'disciplineId', 'originatorId'],
       }
     );
     if (!correspondence)
@@ -285,10 +285,17 @@ export class TransmittalService {
       }
     }
 
-    // เริ่ม Workflow Instance สำหรับ Transmittal
-    const statusDraft = await this.statusRepo.findOne({
-      where: { statusCode: 'DRAFT' },
-    });
+    // Bug 1 fix: ป้องกัน duplicate instance — ถ้ามี Active Instance อยู่แล้ว ให้หยุด
+    const existingInstance = await this.workflowEngine.getInstanceByEntity(
+      'transmittal',
+      correspondence.id.toString()
+    );
+    if (existingInstance) {
+      throw new ValidationException(
+        `Transmittal นี้ถูก Submit ไปแล้ว (Workflow Instance: ${existingInstance.id})`
+      );
+    }
+
     // [C3] Resolve contractId from discipline for contract-scoped workflow
     let contractId: number | null = null;
     if (correspondence.disciplineId) {
@@ -298,11 +305,17 @@ export class TransmittalService {
       );
       contractId = rows[0]?.contract_id ?? null;
     }
+
+    // Bug 2 fix: ใส่ organizationId ใน context เพื่อให้ WorkflowTransitionGuard Level 2 (Org Admin) ทำงานได้
     const instance = await this.workflowEngine.createInstance(
       'TRANSMITTAL_FLOW_V1',
       'transmittal',
       correspondence.id.toString(),
-      { ownerId: user.user_id, contractId }
+      {
+        ownerId: user.user_id,
+        contractId,
+        organizationId: correspondence.originatorId ?? null,
+      }
     );
 
     const result = await this.workflowEngine.processTransition(
@@ -313,18 +326,16 @@ export class TransmittalService {
     );
 
     // Sync สถานะกลับที่ Correspondence Revision
-    if (statusDraft) {
-      const revision = await this.revisionRepo.findOne({
-        where: { correspondenceId: correspondence.id, isCurrent: true },
+    const revision = await this.revisionRepo.findOne({
+      where: { correspondenceId: correspondence.id, isCurrent: true },
+    });
+    if (revision) {
+      const submittedStatus = await this.statusRepo.findOne({
+        where: { statusCode: 'SUBMITTED' },
       });
-      if (revision) {
-        const submittedStatus = await this.statusRepo.findOne({
-          where: { statusCode: 'SUBMITTED' },
-        });
-        if (submittedStatus) {
-          revision.statusId = submittedStatus.id;
-          await this.revisionRepo.save(revision);
-        }
+      if (submittedStatus) {
+        revision.statusId = submittedStatus.id;
+        await this.revisionRepo.save(revision);
       }
     }
 
diff --git a/backend/src/modules/workflow-engine/workflow-engine.controller.ts b/backend/src/modules/workflow-engine/workflow-engine.controller.ts
index b340ec8..624eab1 100644
--- a/backend/src/modules/workflow-engine/workflow-engine.controller.ts
+++ b/backend/src/modules/workflow-engine/workflow-engine.controller.ts
@@ -116,7 +116,7 @@ export class WorkflowEngineController {
       throw new BadRequestException('Idempotency-Key header is required');
     }
 
-    const userId = req.user?.user_id;
+    const userId = req.user.user_id;
 
     // ตรวจ Redis ว่า Request นี้ถูกส่งมาแล้วหรือไม่ (key ผูกกับ userId ป้องกัน cross-user replay)
     const cacheKey = `idempotency:transition:${idempotencyKey}:${userId}`;
@@ -154,9 +154,18 @@ export class WorkflowEngineController {
   @ApiOperation({
     summary: 'ดึงรายการปุ่ม Action ที่สามารถกดได้ ณ สถานะปัจจุบัน',
   })
-  @RequirePermission('document.view') // ผู้ที่มีสิทธิ์ดูเอกสาร ควรดู Action ได้
-  getAvailableActions(@Param('id') _instanceId: string) {
-    // Note: Logic การดึง Action ตาม Instance ID จะถูก Implement ใน Task ถัดไป
-    return { message: 'Pending implementation in Service layer' };
+  @ApiParam({ name: 'id', description: 'Workflow Instance ID (UUID)' })
+  @RequirePermission('document.view')
+  async getAvailableActions(@Param('id') instanceId: string) {
+    const instance = await this.workflowService.getInstanceById(instanceId);
+    const actions = await this.workflowService.getAvailableActions(
+      instance.definition.workflow_code,
+      instance.currentState
+    );
+    return {
+      instanceId,
+      currentState: instance.currentState,
+      availableActions: actions,
+    };
   }
 }
diff --git a/backend/src/modules/workflow-engine/workflow-engine.service.ts b/backend/src/modules/workflow-engine/workflow-engine.service.ts
index 1f9a05f..9b07ee4 100644
--- a/backend/src/modules/workflow-engine/workflow-engine.service.ts
+++ b/backend/src/modules/workflow-engine/workflow-engine.service.ts
@@ -387,7 +387,13 @@ export class WorkflowEngineService {
       await queryRunner.commitTransaction();
 
       // ADR-021 T043: Invalidate Workflow History cache หลัง transition สำเร็จ
-      void this.cacheManager.del(`wf:history:${instanceId}`);
+      this.cacheManager
+        .del(`wf:history:${instanceId}`)
+        .catch((e: unknown) =>
+          this.logger.warn(
+            `Cache invalidation failed for wf:history:${instanceId} — stale data may be served. Error: ${e instanceof Error ? e.message : String(e)}`
+          )
+        );
 
       // [NEW] เก็บค่าไว้ Dispatch หลัง Commit
       eventsToDispatch = evaluation.events;
diff --git a/frontend/app/(dashboard)/transmittals/[uuid]/page.tsx b/frontend/app/(dashboard)/transmittals/[uuid]/page.tsx
index e71e353..7b5f08d 100644
--- a/frontend/app/(dashboard)/transmittals/[uuid]/page.tsx
+++ b/frontend/app/(dashboard)/transmittals/[uuid]/page.tsx
@@ -60,7 +60,9 @@ export default function TransmittalDetailPage() {
 
   const transmittalDocNo = transmittal.correspondence?.correspondenceNumber ?? transmittal.transmittalNo ?? '';
   const transmittalSubject = transmittal.subject ?? '';
-  const transmittalStatus = transmittal.purpose ?? '';
+  const transmittalStatus = transmittal.workflowInstanceId
+    ? (transmittal.workflowState ?? 'SUBMITTED')
+    : 'DRAFT';
 
   return (
     <section className="space-y-4">
diff --git a/frontend/components/workflow/workflow-lifecycle.tsx b/frontend/components/workflow/workflow-lifecycle.tsx
index e00c246..814b1e5 100644
--- a/frontend/components/workflow/workflow-lifecycle.tsx
+++ b/frontend/components/workflow/workflow-lifecycle.tsx
@@ -294,7 +294,7 @@ export function WorkflowLifecycle({
                     type="button"
                     className="ml-0.5 hover:text-destructive"
                     onClick={(e) => { e.stopPropagation(); removeUploadedFile(f.publicId); }}
-                    aria-label={t('workflow.timeline.uploadError')}
+                    aria-label={t('workflow.timeline.removeFile')}
                   >
                     <XIcon className="h-3 w-3" />
                   </button>
diff --git a/frontend/public/locales/en/common.json b/frontend/public/locales/en/common.json
index 1d96dc4..47615e8 100644
--- a/frontend/public/locales/en/common.json
+++ b/frontend/public/locales/en/common.json
@@ -29,6 +29,7 @@
   "workflow.timeline.uploading": "Uploading...",
   "workflow.timeline.uploadTypes": "PDF, DOCX, XLSX, DWG, ZIP · Max 50 MB",
   "workflow.timeline.uploadError": "Unable to upload",
+  "workflow.timeline.removeFile": "Remove file",
 
   "filePreview.fallbackTitle": "File",
   "filePreview.fileUnavailable": "File has been removed from storage.",
diff --git a/frontend/public/locales/th/common.json b/frontend/public/locales/th/common.json
index e04ea21..774c3ed 100644
--- a/frontend/public/locales/th/common.json
+++ b/frontend/public/locales/th/common.json
@@ -29,6 +29,7 @@
   "workflow.timeline.uploading": "กำลังอัปโหลด...",
   "workflow.timeline.uploadTypes": "PDF, DOCX, XLSX, DWG, ZIP · สูงสุด 50 MB",
   "workflow.timeline.uploadError": "ไม่สามารถอัปโหลด",
+  "workflow.timeline.removeFile": "ลบไฟล์",
 
   "filePreview.fallbackTitle": "ไฟล์",
   "filePreview.fileUnavailable": "ไฟล์ถูกลบออกจาก Storage แล้ว",