diff --git a/backend-spring/src/main/java/com/erp/security/SecurityConfig.java b/backend-spring/src/main/java/com/erp/security/SecurityConfig.java
index 7a88baee..7f8859f5 100644
--- a/backend-spring/src/main/java/com/erp/security/SecurityConfig.java
+++ b/backend-spring/src/main/java/com/erp/security/SecurityConfig.java
@@ -2,6 +2,7 @@ package com.erp.security;
 
 import com.erp.ai.security.AiApiKeyAuthFilter;
 import com.erp.ai.service.AiAgentApiKeyService;
+import com.erp.service.SubstituteService;
 import com.erp.tenant.CompanyResolver;
 import com.erp.tenant.SubdomainResolverFilter;
 import com.erp.tenant.TenantDbSettings;
@@ -37,6 +38,7 @@ public class SecurityConfig {
     private final TenantRoutingDataSource tenantRoutingDataSource;
     private final TenantDbSettings tenantDbSettings;
     private final AiAgentApiKeyService aiAgentApiKeyService;
+    private final SubstituteService substituteService;
 
     /**
      * CORS 화이트리스트. 콤마 구분 문자열로 주입 (예: "http://localhost:3000,https://v1.invyone.com").
@@ -76,9 +78,12 @@ public class SecurityConfig {
                 // JwtAuthenticationFilter 뒤 — JWT.company_code 와 서브도메인의 company_code 대조.
                 .addFilterAfter(new TenantConsistencyGuardFilter(jwtTokenProvider),
                         JwtAuthenticationFilter.class)
-                // TenantConsistencyGuardFilter 뒤 — 비번 강제 변경 대기자는 허용 경로만 통과.
+                // TenantConsistencyGuardFilter 뒤 — 대무자(代務者) 컨텍스트 effective_user_ids 주입.
+                .addFilterAfter(new SubstituteContextFilter(substituteService),
+                        TenantConsistencyGuardFilter.class)
+                // SubstituteContextFilter 뒤 — 비번 강제 변경 대기자는 허용 경로만 통과.
                 .addFilterAfter(new ForcePasswordChangeGuardFilter(jwtTokenProvider),
-                        TenantConsistencyGuardFilter.class);
+                        SubstituteContextFilter.class);
 
         return http.build();
     }
diff --git a/backend-spring/src/main/java/com/erp/security/SubstituteContextFilter.java b/backend-spring/src/main/java/com/erp/security/SubstituteContextFilter.java
new file mode 100644
index 00000000..a9e947f2
--- /dev/null
+++ b/backend-spring/src/main/java/com/erp/security/SubstituteContextFilter.java
@@ -0,0 +1,88 @@
+package com.erp.security;
+
+import com.erp.service.SubstituteService;
+import jakarta.servlet.FilterChain;
+import jakarta.servlet.ServletException;
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.web.filter.OncePerRequestFilter;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 대무자(代務者) 컨텍스트 주입 필터.
+ *
+ * Spec: .omc/specs/deep-dive-user-substitute-management.md
+ * Plan: .omc/plans/autopilot-impl.md (T5)
+ *
+ * 동작:
+ *   1. /api/** 가 아니면 통과
+ *   2. JWT user_id / company_code attribute 없으면 통과 (비로그인)
+ *   3. company_code == "*" (SUPER_ADMIN pre-switch) 이면 통과 — 대무 의미 없음
+ *   4. substituteService.getActiveOriginalUserIds(userId, companyCode) 조회
+ *   5. effective_user_ids = [userId, ...originalIds] → request attribute
+ *   6. actual_processor_id = userId → request attribute (의미 명시 alias)
+ *
+ * 예외 처리:
+ *   DB 조회 실패 시 effective_user_ids 를 [userId] 만 담아 통과시킨다 — 대무 컨텍스트
+ *   실패가 본 요청을 깨면 안 되기 때문 (가용성 우선). warn 로그 남김.
+ *
+ * 성능:
+ *   - request 당 SELECT 1회 (인덱스 (COMPANY_CODE, PROXY_USER_ID, IS_ACTIVE) 매치, 보통 <1ms)
+ *   - request-scope 자연 캐시 — 한 요청 내에서 attribute 만 참조하면 추가 조회 없음
+ *
+ * 필터 순서:
+ *   SubdomainResolver → AiApiKey → Jwt → TenantConsistencyGuard → **여기** → ForcePasswordChangeGuard
+ */
+@Slf4j
+@RequiredArgsConstructor
+public class SubstituteContextFilter extends OncePerRequestFilter {
+
+    public static final String ATTR_EFFECTIVE_USER_IDS = "effective_user_ids";
+    public static final String ATTR_ACTUAL_PROCESSOR_ID = "actual_processor_id";
+
+    private final SubstituteService substituteService;
+
+    @Override
+    protected void doFilterInternal(HttpServletRequest request,
+                                    HttpServletResponse response,
+                                    FilterChain chain) throws ServletException, IOException {
+        String path = request.getRequestURI();
+        if (path == null || !path.startsWith("/api/")) {
+            chain.doFilter(request, response);
+            return;
+        }
+
+        String userId = (String) request.getAttribute("user_id");
+        String companyCode = (String) request.getAttribute("company_code");
+
+        // 비로그인 또는 SUPER_ADMIN pre-switch → 대무 컨텍스트 의미 없음, 통과
+        if (userId == null || companyCode == null || "*".equals(companyCode)) {
+            chain.doFilter(request, response);
+            return;
+        }
+
+        List<String> effectiveIds = new ArrayList<>();
+        effectiveIds.add(userId);
+
+        try {
+            List<String> originalIds = substituteService.getActiveOriginalUserIds(userId, companyCode);
+            if (originalIds != null && !originalIds.isEmpty()) {
+                effectiveIds.addAll(originalIds);
+            }
+        } catch (Exception e) {
+            // 대무 컨텍스트 조회 실패는 본 요청을 막지 않음 — 본인 권한만으로 동작
+            log.warn("[SubstituteContext] failed to resolve proxy context for user={}: {}",
+                    userId, e.getMessage());
+        }
+
+        request.setAttribute(ATTR_EFFECTIVE_USER_IDS, effectiveIds);
+        request.setAttribute(ATTR_ACTUAL_PROCESSOR_ID, userId);
+
+        chain.doFilter(request, response);
+    }
+}