diff --git a/backend/src/main/java/com/yoyuzh/api/v2/files/UploadSessionV2Controller.java b/backend/src/main/java/com/yoyuzh/api/v2/files/UploadSessionV2Controller.java
index d71b810..5e019be 100644
--- a/backend/src/main/java/com/yoyuzh/api/v2/files/UploadSessionV2Controller.java
+++ b/backend/src/main/java/com/yoyuzh/api/v2/files/UploadSessionV2Controller.java
@@ -53,6 +53,13 @@ public class UploadSessionV2Controller {
         return ApiV2Response.success(toResponse(uploadSessionService.cancelOwnedSession(user, sessionId)));
     }
 
+    @PostMapping("/{sessionId}/complete")
+    public ApiV2Response<UploadSessionV2Response> completeSession(@AuthenticationPrincipal UserDetails userDetails,
+                                                                  @PathVariable String sessionId) {
+        User user = userDetailsService.loadDomainUser(userDetails.getUsername());
+        return ApiV2Response.success(toResponse(uploadSessionService.completeOwnedSession(user, sessionId)));
+    }
+
     private UploadSessionV2Response toResponse(UploadSession session) {
         return new UploadSessionV2Response(
                 session.getSessionId(),
diff --git a/backend/src/main/java/com/yoyuzh/files/UploadSessionService.java b/backend/src/main/java/com/yoyuzh/files/UploadSessionService.java
index 8c8f9e7..2e22aa8 100644
--- a/backend/src/main/java/com/yoyuzh/files/UploadSessionService.java
+++ b/backend/src/main/java/com/yoyuzh/files/UploadSessionService.java
@@ -21,22 +21,26 @@ public class UploadSessionService {
 
     private final UploadSessionRepository uploadSessionRepository;
     private final StoredFileRepository storedFileRepository;
+    private final FileService fileService;
     private final long maxFileSize;
     private final Clock clock;
 
     @Autowired
     public UploadSessionService(UploadSessionRepository uploadSessionRepository,
                                 StoredFileRepository storedFileRepository,
+                                FileService fileService,
                                 FileStorageProperties properties) {
-        this(uploadSessionRepository, storedFileRepository, properties, Clock.systemUTC());
+        this(uploadSessionRepository, storedFileRepository, fileService, properties, Clock.systemUTC());
     }
 
     UploadSessionService(UploadSessionRepository uploadSessionRepository,
                          StoredFileRepository storedFileRepository,
+                         FileService fileService,
                          FileStorageProperties properties,
                          Clock clock) {
         this.uploadSessionRepository = uploadSessionRepository;
         this.storedFileRepository = storedFileRepository;
+        this.fileService = fileService;
         this.maxFileSize = properties.getMaxFileSize();
         this.clock = clock;
     }
@@ -83,6 +87,46 @@ public class UploadSessionService {
         return uploadSessionRepository.save(session);
     }
 
+    @Transactional
+    public UploadSession completeOwnedSession(User user, String sessionId) {
+        UploadSession session = getOwnedSession(user, sessionId);
+        if (session.getStatus() == UploadSessionStatus.COMPLETED) {
+            return session;
+        }
+        if (session.getStatus() == UploadSessionStatus.CANCELLED || session.getStatus() == UploadSessionStatus.FAILED) {
+            throw new BusinessException(ErrorCode.UNKNOWN, "上传会话不能完成");
+        }
+        LocalDateTime now = LocalDateTime.ofInstant(clock.instant(), clock.getZone());
+        if (session.getExpiresAt().isBefore(now)) {
+            session.setStatus(UploadSessionStatus.EXPIRED);
+            session.setUpdatedAt(now);
+            uploadSessionRepository.save(session);
+            throw new BusinessException(ErrorCode.UNKNOWN, "上传会话已过期");
+        }
+
+        session.setStatus(UploadSessionStatus.COMPLETING);
+        session.setUpdatedAt(now);
+        uploadSessionRepository.save(session);
+
+        try {
+            fileService.completeUpload(user, new CompleteUploadRequest(
+                    session.getTargetPath(),
+                    session.getFilename(),
+                    session.getObjectKey(),
+                    session.getContentType(),
+                    session.getSize()
+            ));
+            session.setStatus(UploadSessionStatus.COMPLETED);
+            session.setUpdatedAt(now);
+            return uploadSessionRepository.save(session);
+        } catch (RuntimeException ex) {
+            session.setStatus(UploadSessionStatus.FAILED);
+            session.setUpdatedAt(now);
+            uploadSessionRepository.save(session);
+            throw ex;
+        }
+    }
+
     private void validateTarget(User user, String normalizedPath, String filename, long size) {
         long effectiveMaxUploadSize = Math.min(maxFileSize, user.getMaxUploadSizeBytes());
         if (size > effectiveMaxUploadSize) {
diff --git a/backend/src/test/java/com/yoyuzh/api/v2/files/UploadSessionV2ControllerTest.java b/backend/src/test/java/com/yoyuzh/api/v2/files/UploadSessionV2ControllerTest.java
index 5666f41..aebc94f 100644
--- a/backend/src/test/java/com/yoyuzh/api/v2/files/UploadSessionV2ControllerTest.java
+++ b/backend/src/test/java/com/yoyuzh/api/v2/files/UploadSessionV2ControllerTest.java
@@ -87,6 +87,22 @@ class UploadSessionV2ControllerTest {
                 .andExpect(jsonPath("$.data.status").value("CREATED"));
     }
 
+    @Test
+    void shouldCompleteUploadSessionWithV2Envelope() throws Exception {
+        User user = createUser(7L);
+        UploadSession session = createSession(user);
+        session.setStatus(UploadSessionStatus.COMPLETED);
+        when(userDetailsService.loadDomainUser("alice")).thenReturn(user);
+        when(uploadSessionService.completeOwnedSession(user, "session-1")).thenReturn(session);
+
+        mockMvc.perform(post("/api/v2/files/upload-sessions/session-1/complete")
+                        .with(user(userDetails())))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.code").value(0))
+                .andExpect(jsonPath("$.data.sessionId").value("session-1"))
+                .andExpect(jsonPath("$.data.status").value("COMPLETED"));
+    }
+
     private UserDetails userDetails() {
         return org.springframework.security.core.userdetails.User
                 .withUsername("alice")
diff --git a/backend/src/test/java/com/yoyuzh/files/UploadSessionServiceTest.java b/backend/src/test/java/com/yoyuzh/files/UploadSessionServiceTest.java
index 49575b9..f67f75d 100644
--- a/backend/src/test/java/com/yoyuzh/files/UploadSessionServiceTest.java
+++ b/backend/src/test/java/com/yoyuzh/files/UploadSessionServiceTest.java
@@ -6,6 +6,7 @@ import com.yoyuzh.config.FileStorageProperties;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.ArgumentCaptor;
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
 
@@ -18,7 +19,9 @@ import java.util.Optional;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.verify;
 
 @ExtendWith(MockitoExtension.class)
 class UploadSessionServiceTest {
@@ -27,6 +30,8 @@ class UploadSessionServiceTest {
     private UploadSessionRepository uploadSessionRepository;
     @Mock
     private StoredFileRepository storedFileRepository;
+    @Mock
+    private FileService fileService;
 
     private UploadSessionService uploadSessionService;
 
@@ -37,6 +42,7 @@ class UploadSessionServiceTest {
         uploadSessionService = new UploadSessionService(
                 uploadSessionRepository,
                 storedFileRepository,
+                fileService,
                 properties,
                 Clock.fixed(Instant.parse("2026-04-08T06:00:00Z"), ZoneOffset.UTC)
         );
@@ -91,6 +97,39 @@ class UploadSessionServiceTest {
         )).isInstanceOf(BusinessException.class);
     }
 
+    @Test
+    void shouldCompleteOwnedSessionThroughLegacyFileCommitPath() {
+        User user = createUser(7L);
+        UploadSession session = createSession(user);
+        when(uploadSessionRepository.findBySessionIdAndUserId("session-1", 7L))
+                .thenReturn(Optional.of(session));
+        when(uploadSessionRepository.save(any(UploadSession.class))).thenAnswer(invocation -> invocation.getArgument(0));
+
+        UploadSession result = uploadSessionService.completeOwnedSession(user, "session-1");
+
+        assertThat(result.getStatus()).isEqualTo(UploadSessionStatus.COMPLETED);
+        assertThat(result.getUpdatedAt()).isEqualTo(LocalDateTime.of(2026, 4, 8, 6, 0));
+        ArgumentCaptor<CompleteUploadRequest> requestCaptor = ArgumentCaptor.forClass(CompleteUploadRequest.class);
+        verify(fileService).completeUpload(eq(user), requestCaptor.capture());
+        assertThat(requestCaptor.getValue().path()).isEqualTo("/docs");
+        assertThat(requestCaptor.getValue().filename()).isEqualTo("movie.mp4");
+        assertThat(requestCaptor.getValue().storageName()).isEqualTo("blobs/session-1");
+        assertThat(requestCaptor.getValue().contentType()).isEqualTo("video/mp4");
+        assertThat(requestCaptor.getValue().size()).isEqualTo(20L);
+    }
+
+    @Test
+    void shouldRejectCompletingCancelledSession() {
+        User user = createUser(7L);
+        UploadSession session = createSession(user);
+        session.setStatus(UploadSessionStatus.CANCELLED);
+        when(uploadSessionRepository.findBySessionIdAndUserId("session-1", 7L))
+                .thenReturn(Optional.of(session));
+
+        assertThatThrownBy(() -> uploadSessionService.completeOwnedSession(user, "session-1"))
+                .isInstanceOf(BusinessException.class);
+    }
+
     private User createUser(Long id) {
         User user = new User();
         user.setId(id);
@@ -100,4 +139,23 @@ class UploadSessionServiceTest {
         user.setCreatedAt(LocalDateTime.now());
         return user;
     }
+
+    private UploadSession createSession(User user) {
+        UploadSession session = new UploadSession();
+        session.setSessionId("session-1");
+        session.setUser(user);
+        session.setTargetPath("/docs");
+        session.setFilename("movie.mp4");
+        session.setContentType("video/mp4");
+        session.setSize(20L);
+        session.setObjectKey("blobs/session-1");
+        session.setChunkSize(8L * 1024 * 1024);
+        session.setChunkCount(1);
+        session.setUploadedPartsJson("[]");
+        session.setStatus(UploadSessionStatus.CREATED);
+        session.setCreatedAt(LocalDateTime.of(2026, 4, 8, 6, 0));
+        session.setUpdatedAt(LocalDateTime.of(2026, 4, 8, 6, 0));
+        session.setExpiresAt(LocalDateTime.of(2026, 4, 9, 6, 0));
+        return session;
+    }
 }
diff --git a/docs/api-reference.md b/docs/api-reference.md
index 023d772..3a3410d 100644
--- a/docs/api-reference.md
+++ b/docs/api-reference.md
@@ -442,3 +442,4 @@
 - 后端在旧接口内部开始双写实体模型：上传完成、外部导入、分享导入和网盘复制会继续写 `FileBlob`，同时创建或复用 `FileEntity.VERSION`，并写入 `StoredFile.primaryEntity` 与 `StoredFileEntity(PRIMARY)`。
 - 下载、分享详情、回收站、ZIP 下载仍读取 `StoredFile.blob`；后续阶段稳定后再切换到 `primaryEntity` 读取。
 - 2026-04-08 阶段 3 第一小步 API 补充：新增受保护的 v2 上传会话骨架接口，`POST /api/v2/files/upload-sessions` 创建会话，`GET /api/v2/files/upload-sessions/{sessionId}` 查询当前用户自己的会话，`DELETE /api/v2/files/upload-sessions/{sessionId}` 取消会话。当前响应只返回 `sessionId`、`objectKey`、路径、文件名、状态、分片大小、分片数量和时间字段；实际文件内容仍走旧上传链路，尚未开放 v2 分片上传/完成接口。
+- 2026-04-08 阶段 3 第二小步 API 补充：新增 `POST /api/v2/files/upload-sessions/{sessionId}/complete`，用于把当前用户自己的上传会话提交完成。该接口当前不接收请求体，会复用会话里的 `objectKey/path/filename/contentType/size` 调用旧上传完成落库链路，成功后返回 `COMPLETED` 状态的 v2 会话响应；分片内容上传端点仍未开放。
diff --git a/docs/architecture.md b/docs/architecture.md
index e3a3591..34add8d 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -446,3 +446,4 @@ Android 壳补充说明：
 - `StoredFile.blob` 仍是当前生产读取路径；`StoredFile.primaryEntity` 与关系表暂时只作为兼容迁移数据，不影响旧 `/api/files/**` DTO 和前端调用。
 - `portal_stored_file_entity.stored_file_id` 随 `portal_file` 删除级联清理；`portal_file_entity.created_by` 在用户删除时置空，避免实体审计关系阻塞用户清理。
 - 2026-04-08 阶段 3 第一小步补充：后端新增上传会话二期最小骨架。`UploadSession` 记录用户、目标路径、文件名、对象键、分片大小、分片数量、状态、过期时间和已上传分片占位 JSON；`/api/v2/files/upload-sessions` 目前只提供创建、查询、取消会话，不承接实际分片内容上传，也不替换旧 `/api/files/upload/**` 生产链路。
+- 2026-04-08 阶段 3 第二小步补充：上传会话新增完成状态机。`UploadSessionService.completeOwnedSession()` 会复用旧 `FileService.completeUpload()` 完成对象确认、目录补齐、配额/冲突校验和 `FileBlob + StoredFile + FileEntity.VERSION` 双写落库，然后把会话标记为 `COMPLETED`；失败时标记 `FAILED`，过期时标记 `EXPIRED`。当前仍没有独立 v2 分片内容写入端点。
diff --git a/memory.md b/memory.md
index 2595028..943adfc 100644
--- a/memory.md
+++ b/memory.md
@@ -160,3 +160,4 @@
 - 当前仍不切换读取路径：下载、ZIP、分享详情、回收站等旧业务继续依赖 `StoredFile.blob`，`primaryEntity` 只作为后续版本、缩略图、转码、存储策略迁移的兼容数据。
 - 为避免新关系表阻塞现有删除和测试清理，`StoredFileEntity -> StoredFile` 使用数据库级删除级联；`FileEntity.createdBy` 删除用户时置空，保留物理实体审计数据但不阻塞用户清理。
 - 2026-04-08 阶段 3 第一小步：新增后端上传会话二期最小骨架，包含 `UploadSession`、`UploadSessionStatus`、`UploadSessionRepository`、`UploadSessionService`，以及受保护的 `/api/v2/files/upload-sessions` 创建、查询、取消接口；旧 `/api/files/upload/**` 上传链路暂不切换，前端上传队列暂不改动。
+- 2026-04-08 阶段 3 第二小步：新增 `POST /api/v2/files/upload-sessions/{sessionId}/complete`，v2 上传会话可从 `CREATED` 进入 `COMPLETING` 并复用旧 `FileService.completeUpload()` 完成 `FileBlob + StoredFile + FileEntity.VERSION` 落库，成功后标记 `COMPLETED`；取消、失败、过期会话不能完成。实际分片内容上传和前端上传队列仍未切换。