diff --git a/.agents/skills/bugfix/SKILL.md b/.agents/skills/bugfix/SKILL.md
index d5b7d578..66af7431 100644
--- a/.agents/skills/bugfix/SKILL.md
+++ b/.agents/skills/bugfix/SKILL.md
@@ -1,10 +1,7 @@
-// File: .agents/skills/bugfix/SKILL.md
-// Change Log: 2026-05-13 - Initial version improved from docs/bugfix.md
-
 ---
 name: bugfix
 description: Quick bugfix workflow with minimal impact. Focused on surgical fixes without unrelated refactoring.
-version: 1.0.0
+version: 1.9.0
 ---
 
 # Bugfix
@@ -29,7 +26,7 @@ version: 1.0.0
 ## Phase 3 — Execution (การดำเนินการ)
 
 1. **Apply Fix**: ลงมือแก้ไขโค้ดตามแผน
-2. **Verify Fix**: 
+2. **Verify Fix**:
    - จำลองสถานการณ์เพื่อยืนยันว่า Bug หายไปจริง
    - ตรวจสอบว่าไม่มี Forbidden Patterns (`any`, `console.log`, UUID misuse)
 3. **Regression Check**: ตรวจสอบส่วนที่เกี่ยวข้องว่ายังทำงานได้ปกติ
diff --git a/.windsurf/skills/bugfix/SKILL.md b/.windsurf/skills/bugfix/SKILL.md
index d5b7d578..66af7431 100644
--- a/.windsurf/skills/bugfix/SKILL.md
+++ b/.windsurf/skills/bugfix/SKILL.md
@@ -1,10 +1,7 @@
-// File: .agents/skills/bugfix/SKILL.md
-// Change Log: 2026-05-13 - Initial version improved from docs/bugfix.md
-
 ---
 name: bugfix
 description: Quick bugfix workflow with minimal impact. Focused on surgical fixes without unrelated refactoring.
-version: 1.0.0
+version: 1.9.0
 ---
 
 # Bugfix
@@ -29,7 +26,7 @@ version: 1.0.0
 ## Phase 3 — Execution (การดำเนินการ)
 
 1. **Apply Fix**: ลงมือแก้ไขโค้ดตามแผน
-2. **Verify Fix**: 
+2. **Verify Fix**:
    - จำลองสถานการณ์เพื่อยืนยันว่า Bug หายไปจริง
    - ตรวจสอบว่าไม่มี Forbidden Patterns (`any`, `console.log`, UUID misuse)
 3. **Regression Check**: ตรวจสอบส่วนที่เกี่ยวข้องว่ายังทำงานได้ปกติ
diff --git a/backend/tests/unit/delegation/circular-detection.service.spec.ts b/backend/tests/unit/delegation/circular-detection.service.spec.ts
index 5649621b..539a338e 100644
--- a/backend/tests/unit/delegation/circular-detection.service.spec.ts
+++ b/backend/tests/unit/delegation/circular-detection.service.spec.ts
@@ -1,17 +1,75 @@
 // File: tests/unit/delegation/circular-detection.service.spec.ts
+// Change Log
+// - 2026-05-13: ปรับ mock repository ให้ตรงกับ QueryBuilder contract ของ CircularDetectionService
 // Unit tests สำหรับ CircularDetectionService — ป้องกัน delegation loops (T075)
 import { Test, TestingModule } from '@nestjs/testing';
 import { getRepositoryToken } from '@nestjs/typeorm';
 import { CircularDetectionService } from '../../../src/modules/delegation/services/circular-detection.service';
 import { Delegation } from '../../../src/modules/delegation/entities/delegation.entity';
 
-const mockDelegationRepo = {
-  find: jest.fn(),
+type DelegationRow = Pick<Delegation, 'delegatorUserId' | 'delegateUserId'>;
+
+type QueryBuilderMock = {
+  where: jest.MockedFunction<
+    (
+      condition: string,
+      parameters?: Record<string, unknown>
+    ) => QueryBuilderMock
+  >;
+  andWhere: jest.MockedFunction<
+    (
+      condition: string,
+      parameters?: Record<string, unknown>
+    ) => QueryBuilderMock
+  >;
+  select: jest.MockedFunction<(selection: string[]) => QueryBuilderMock>;
+  getMany: jest.MockedFunction<() => Promise<DelegationRow[]>>;
+};
+
+type DelegationRepositoryMock = {
+  createQueryBuilder: jest.MockedFunction<(alias: string) => QueryBuilderMock>;
+};
+
+const createQueryBuilderMock = (
+  delegations: DelegationRow[]
+): QueryBuilderMock => {
+  const queryBuilder = {} as QueryBuilderMock;
+  queryBuilder.where = jest.fn(
+    (
+      _condition: string,
+      _parameters?: Record<string, unknown>
+    ): QueryBuilderMock => queryBuilder
+  );
+  queryBuilder.andWhere = jest.fn(
+    (
+      _condition: string,
+      _parameters?: Record<string, unknown>
+    ): QueryBuilderMock => queryBuilder
+  );
+  queryBuilder.select = jest.fn(
+    (_selection: string[]): QueryBuilderMock => queryBuilder
+  );
+  queryBuilder.getMany = jest.fn(
+    (): Promise<DelegationRow[]> => Promise.resolve(delegations)
+  );
+  return queryBuilder;
+};
+
+const mockDelegationRepo: DelegationRepositoryMock = {
+  createQueryBuilder: jest.fn(),
 };
 
 describe('CircularDetectionService', () => {
   let service: CircularDetectionService;
 
+  const mockActiveDelegations = (
+    delegations: DelegationRow[]
+  ): QueryBuilderMock => {
+    const queryBuilder = createQueryBuilderMock(delegations);
+    mockDelegationRepo.createQueryBuilder.mockReturnValue(queryBuilder);
+    return queryBuilder;
+  };
+
   beforeEach(async () => {
     const module: TestingModule = await Test.createTestingModule({
       providers: [
@@ -33,16 +91,14 @@ describe('CircularDetectionService', () => {
 
   describe('wouldCreateCircle', () => {
     it('should return false when no delegations exist', async () => {
-      mockDelegationRepo.find.mockResolvedValue([]);
+      mockActiveDelegations([]);
       const result = await service.wouldCreateCircle(1, 2);
       expect(result).toBe(false);
     });
 
     it('should detect direct circular delegation A→B when B→A exists', async () => {
       // B (id=2) delegates to A (id=1)
-      mockDelegationRepo.find.mockResolvedValue([
-        { delegatorId: 2, delegateId: 1 },
-      ]);
+      mockActiveDelegations([{ delegatorUserId: 2, delegateUserId: 1 }]);
       // Now trying to add A→B — would create cycle
       const result = await service.wouldCreateCircle(1, 2);
       expect(result).toBe(true);
@@ -50,9 +106,9 @@ describe('CircularDetectionService', () => {
 
     it('should detect indirect cycle A→B→C when trying C→A', async () => {
       // A→B and B→C already exist
-      mockDelegationRepo.find.mockResolvedValue([
-        { delegatorId: 1, delegateId: 2 },
-        { delegatorId: 2, delegateId: 3 },
+      mockActiveDelegations([
+        { delegatorUserId: 1, delegateUserId: 2 },
+        { delegatorUserId: 2, delegateUserId: 3 },
       ]);
       // Now trying C→A — would create A→B→C→A cycle
       const result = await service.wouldCreateCircle(3, 1);
@@ -61,9 +117,9 @@ describe('CircularDetectionService', () => {
 
     it('should return false for non-circular delegations', async () => {
       // A→B and B→C — adding D→A is fine
-      mockDelegationRepo.find.mockResolvedValue([
-        { delegatorId: 1, delegateId: 2 },
-        { delegatorId: 2, delegateId: 3 },
+      mockActiveDelegations([
+        { delegatorUserId: 1, delegateUserId: 2 },
+        { delegatorUserId: 2, delegateUserId: 3 },
       ]);
       const result = await service.wouldCreateCircle(4, 1);
       expect(result).toBe(false);