feat(cluster): 支持远程源服务器集中备份

为 Master 本地磁盘增加可选流式中转，远程 Agent 可直接把产物写入中央存储并通过反向通道恢复。

持久化并校验传输模式，兼容既有 Agent 本机磁盘目标，补齐鉴权、完整性、配额、访问保护、前端配置及双向链路测试。

Closes #101

server/internal/agent/client.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"crypto/tls"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -125,10 +126,11 @@ type TaskSpec struct {
 
 // StorageTargetConfig 与 service.AgentStorageTargetConfig 对齐
 type StorageTargetConfig struct {
-	ID     uint            `json:"id"`
-	Type   string          `json:"type"`
-	Name   string          `json:"name"`
-	Config json.RawMessage `json:"config"`
+	ID           uint            `json:"id"`
+	Type         string          `json:"type"`
+	Name         string          `json:"name"`
+	Config       json.RawMessage `json:"config"`
+	TransferMode string          `json:"transferMode"`
 }
 
 // GetTaskSpec 拉取任务规格
@@ -149,6 +151,7 @@ type RecordUpdate struct {
 	Checksum             string              `json:"checksum,omitempty"`
 	StoragePath          string              `json:"storagePath,omitempty"`
 	StorageTargetID      uint                `json:"storageTargetId,omitempty"`
+	StorageTransferMode  string              `json:"storageTransferMode,omitempty"`
 	StorageUploadResults []StorageResultItem `json:"storageUploadResults,omitempty"`
 	ErrorMessage         string              `json:"errorMessage,omitempty"`
 	LogAppend            string              `json:"logAppend,omitempty"`
@@ -160,6 +163,7 @@ type StorageResultItem struct {
 	Status            string `json:"status"`
 	StoragePath       string `json:"storagePath,omitempty"`
 	FileSize          int64  `json:"fileSize,omitempty"`
+	TransferMode      string `json:"transferMode,omitempty"`
 	Error             string `json:"error,omitempty"`
 }
 
@@ -169,6 +173,39 @@ func (c *MasterClient) UpdateRecord(ctx context.Context, recordID uint, update R
 	return c.do(ctx, http.MethodPost, path, update, nil)
 }
 
+// UploadArtifact streams an artifact through the Master for storage targets
+// that are not directly reachable from the Agent.
+func (c *MasterClient) UploadArtifact(ctx context.Context, recordID, targetID uint, objectKey string, size int64, checksum string, reader io.Reader) error {
+	path := fmt.Sprintf("/api/agent/records/%d/artifacts/%d", recordID, targetID)
+	req, err := http.NewRequestWithContext(ctx, http.MethodPut, c.baseURL+path, reader)
+	if err != nil {
+		return err
+	}
+	// The executor owns and closes the artifact file. Prevent net/http from
+	// closing that underlying reader when it finishes the request body.
+	req.Body = io.NopCloser(reader)
+	req.ContentLength = size
+	req.Header.Set("Content-Type", "application/octet-stream")
+	req.Header.Set("X-Agent-Token", c.token)
+	req.Header.Set("X-BackupX-Object-Key", objectKey)
+	req.Header.Set("X-BackupX-SHA256", checksum)
+	client := *c.httpClient
+	client.Timeout = 0
+	resp, err := client.Do(req)
+	if err != nil {
+		return fmt.Errorf("relay artifact to Master: %w", err)
+	}
+	data, readErr := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	closeErr := resp.Body.Close()
+	if readErr != nil || closeErr != nil {
+		return errors.Join(readErr, closeErr)
+	}
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return fmt.Errorf("relay artifact to Master: http %d: %s", resp.StatusCode, string(data))
+	}
+	return nil
+}
+
 // RestoreSpec 与 service.AgentRestoreSpec 对齐
 type RestoreSpec struct {
 	RestoreRecordID uint                `json:"restoreRecordId"`
@@ -210,6 +247,27 @@ func (c *MasterClient) GetRestoreSpec(ctx context.Context, restoreRecordID uint)
 	return &spec, nil
 }
 
+func (c *MasterClient) DownloadRestoreArtifact(ctx context.Context, restoreRecordID uint) (io.ReadCloser, error) {
+	path := fmt.Sprintf("/api/agent/restores/%d/artifact", restoreRecordID)
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+path, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("X-Agent-Token", c.token)
+	client := *c.httpClient
+	client.Timeout = 0
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("download relayed artifact from Master: %w", err)
+	}
+	if resp.StatusCode >= 200 && resp.StatusCode < 300 {
+		return resp.Body, nil
+	}
+	data, readErr := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	closeErr := resp.Body.Close()
+	return nil, errors.Join(fmt.Errorf("download relayed artifact from Master: http %d: %s", resp.StatusCode, string(data)), readErr, closeErr)
+}
+
 // UpdateRestore 上报恢复记录的状态/日志
 func (c *MasterClient) UpdateRestore(ctx context.Context, restoreRecordID uint, update RestoreUpdate) error {
 	path := fmt.Sprintf("/api/agent/restores/%d", restoreRecordID)

server/internal/agent/executor.go

@@ -5,6 +5,7 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -137,13 +138,15 @@ func (e *Executor) ExecuteRunTask(ctx context.Context, taskID, recordID uint) er
 	}
 	uploadResults := make([]StorageResultItem, 0, len(spec.StorageTargets))
 	selectedStorageTargetID := uint(0)
+	selectedStorageTransferMode := ""
 	var uploadErrors []string
 	for _, target := range spec.StorageTargets {
-		if err := e.uploadToTarget(ctx, recordID, target, finalPath, storagePath, fileSize, spec.TaskID); err != nil {
+		if err := e.uploadToTarget(ctx, recordID, target, finalPath, storagePath, fileSize, checksum, spec.TaskID); err != nil {
 			uploadResults = append(uploadResults, StorageResultItem{
 				StorageTargetID:   target.ID,
 				StorageTargetName: target.Name,
 				Status:            "failed",
+				TransferMode:      target.TransferMode,
 				Error:             err.Error(),
 			})
 			uploadErrors = append(uploadErrors, fmt.Sprintf("%s: %v", target.Name, err))
@@ -152,6 +155,7 @@ func (e *Executor) ExecuteRunTask(ctx context.Context, taskID, recordID uint) er
 		}
 		if selectedStorageTargetID == 0 {
 			selectedStorageTargetID = target.ID
+			selectedStorageTransferMode = target.TransferMode
 		}
 		uploadResults = append(uploadResults, StorageResultItem{
 			StorageTargetID:   target.ID,
@@ -159,6 +163,7 @@ func (e *Executor) ExecuteRunTask(ctx context.Context, taskID, recordID uint) er
 			Status:            "success",
 			StoragePath:       storagePath,
 			FileSize:          fileSize,
+			TransferMode:      target.TransferMode,
 		})
 		e.appendLog(ctx, recordID, fmt.Sprintf("[agent] 已上传到存储目标 %s\n", target.Name))
 	}
@@ -179,34 +184,40 @@ func (e *Executor) ExecuteRunTask(ctx context.Context, taskID, recordID uint) er
 		Checksum:             checksum,
 		StoragePath:          storagePath,
 		StorageTargetID:      selectedStorageTargetID,
+		StorageTransferMode:  selectedStorageTransferMode,
 		StorageUploadResults: uploadResults,
 		LogAppend:            fmt.Sprintf("[agent] 任务完成，总计 %d 字节\n", fileSize),
 	})
 }
 
 // uploadToTarget 上传单个目标。为保持简化不做上传级重试（rclone 本身已有 low-level 重试）。
-func (e *Executor) uploadToTarget(ctx context.Context, recordID uint, target StorageTargetConfig, filePath, objectKey string, fileSize int64, taskID uint) error {
-	var rawConfig map[string]any
-	if len(target.Config) > 0 {
-		// DecodeRawConfig 通过 json 解析
-		if err := jsonUnmarshalMap(target.Config, &rawConfig); err != nil {
-			return fmt.Errorf("parse storage config: %w", err)
-		}
-	}
-	provider, err := e.storageRegistry.Create(ctx, target.Type, rawConfig)
-	if err != nil {
-		return fmt.Errorf("create provider: %w", err)
-	}
+func (e *Executor) uploadToTarget(ctx context.Context, recordID uint, target StorageTargetConfig, filePath, objectKey string, fileSize int64, checksum string, taskID uint) error {
 	f, err := os.Open(filePath)
 	if err != nil {
 		return fmt.Errorf("open artifact: %w", err)
 	}
-	defer f.Close()
+	if target.TransferMode == storage.TransferModeMasterRelay {
+		uploadErr := e.client.UploadArtifact(ctx, recordID, target.ID, objectKey, fileSize, checksum, f)
+		return errors.Join(uploadErr, f.Close())
+	}
+	var rawConfig map[string]any
+	if len(target.Config) > 0 {
+		// DecodeRawConfig 通过 json 解析
+		if err := jsonUnmarshalMap(target.Config, &rawConfig); err != nil {
+			return errors.Join(fmt.Errorf("parse storage config: %w", err), f.Close())
+		}
+	}
+	provider, err := e.storageRegistry.Create(ctx, target.Type, rawConfig)
+	if err != nil {
+		closeErr := f.Close()
+		return errors.Join(fmt.Errorf("create provider: %w", err), closeErr)
+	}
 	meta := map[string]string{
 		"taskId":   fmt.Sprintf("%d", taskID),
 		"recordId": fmt.Sprintf("%d", recordID),
 	}
-	return provider.Upload(ctx, objectKey, f, fileSize, meta)
+	uploadErr := provider.Upload(ctx, objectKey, f, fileSize, meta)
+	return errors.Join(uploadErr, f.Close())
 }
 
 // appendLog 追加日志到 Master 记录（尽力而为，失败不中断主流程）
@@ -328,7 +339,7 @@ func (e *Executor) DeleteStorageObject(ctx context.Context, targetType string, t
 // ExecuteRestore 处理 restore_record 命令：拉规格 → 下载 → 解压 → 执行 runner.Restore → 上报结果。
 //
 // 与 ExecuteRunTask 对称，但方向相反：
-//   - 下载：通过 spec.Storage 创建 provider → Download(spec.StoragePath)
+//   - 下载：直连共享存储，或通过 Master 中转其本地磁盘对象
 //   - 解密：当前 Agent 不支持加密恢复（密钥未下发），spec.Encrypt=true 会直接失败
 //   - 执行：backup.Registry.Runner(spec.Type).Restore
 //   - 上报：通过 UpdateRestore（status/logAppend）
@@ -357,28 +368,31 @@ func (e *Executor) ExecuteRestore(ctx context.Context, restoreRecordID uint) err
 	}
 	defer os.RemoveAll(tmpDir)
 
-	// 1) 创建 storage provider
-	var rawConfig map[string]any
-	if len(spec.Storage.Config) > 0 {
-		if err := jsonUnmarshalMap(spec.Storage.Config, &rawConfig); err != nil {
-			e.reportRestoreFailure(ctx, restoreRecordID, fmt.Sprintf("解析存储配置失败: %v", err))
-			return err
-		}
-	}
-	provider, err := e.storageRegistry.Create(ctx, spec.Storage.Type, rawConfig)
-	if err != nil {
-		e.reportRestoreFailure(ctx, restoreRecordID, fmt.Sprintf("创建存储客户端失败: %v", err))
-		return err
-	}
-
-	// 2) 下载
+	// 1) 下载
 	fileName := spec.FileName
 	if strings.TrimSpace(fileName) == "" {
 		fileName = filepath.Base(spec.StoragePath)
 	}
 	artifactPath := filepath.Join(tmpDir, filepath.Base(fileName))
 	e.appendRestoreLog(ctx, restoreRecordID, fmt.Sprintf("[agent] 下载备份文件 %s\n", spec.StoragePath))
-	reader, err := provider.Download(ctx, spec.StoragePath)
+	var reader io.ReadCloser
+	if spec.Storage.TransferMode == storage.TransferModeMasterRelay {
+		reader, err = e.client.DownloadRestoreArtifact(ctx, restoreRecordID)
+	} else {
+		var rawConfig map[string]any
+		if len(spec.Storage.Config) > 0 {
+			if err := jsonUnmarshalMap(spec.Storage.Config, &rawConfig); err != nil {
+				e.reportRestoreFailure(ctx, restoreRecordID, fmt.Sprintf("解析存储配置失败: %v", err))
+				return err
+			}
+		}
+		provider, providerErr := e.storageRegistry.Create(ctx, spec.Storage.Type, rawConfig)
+		if providerErr != nil {
+			e.reportRestoreFailure(ctx, restoreRecordID, fmt.Sprintf("创建存储客户端失败: %v", providerErr))
+			return providerErr
+		}
+		reader, err = provider.Download(ctx, spec.StoragePath)
+	}
 	if err != nil {
 		e.reportRestoreFailure(ctx, restoreRecordID, fmt.Sprintf("下载备份失败: %v", err))
 		return err
@@ -489,8 +503,10 @@ func buildRestoreBackupTaskSpec(spec *RestoreSpec, startedAt time.Time, tempDir
 }
 
 // writeReaderToLocal 把 reader 写到本地文件（Agent 侧工具函数）。
-func writeReaderToLocal(targetPath string, reader io.ReadCloser) error {
-	defer reader.Close()
+func writeReaderToLocal(targetPath string, reader io.ReadCloser) (err error) {
+	defer func() {
+		err = errors.Join(err, reader.Close())
+	}()
 	if err := os.MkdirAll(filepath.Dir(targetPath), 0o755); err != nil {
 		return err
 	}
@@ -498,9 +514,8 @@ func writeReaderToLocal(targetPath string, reader io.ReadCloser) error {
 	if err != nil {
 		return err
 	}
-	defer file.Close()
-	_, err = io.Copy(file, reader)
-	return err
+	_, copyErr := io.Copy(file, reader)
+	return errors.Join(copyErr, file.Close())
 }
 
 // 辅助函数

server/internal/agent/executor_test.go

@@ -1,7 +1,10 @@
 package agent
 
 import (
+	"archive/tar"
+	"bytes"
 	"context"
+	"crypto/sha256"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -109,6 +112,149 @@ func TestExecuteRunTaskRecordsPerTargetUploadResults(t *testing.T) {
 	}
 }
 
+func TestExecuteRunTaskRelaysMasterLocalDiskTarget(t *testing.T) {
+	sourceDir := t.TempDir()
+	if err := os.WriteFile(filepath.Join(sourceDir, "index.html"), []byte("centralize me"), 0o644); err != nil {
+		t.Fatalf("WriteFile returned error: %v", err)
+	}
+	var relayed []byte
+	var finalUpdate RecordUpdate
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch {
+		case r.Method == http.MethodGet && r.URL.Path == "/api/agent/tasks/1":
+			writeAgentEnvelope(t, w, TaskSpec{
+				TaskID:      1,
+				Name:        "remote-source",
+				Type:        "file",
+				SourcePath:  sourceDir,
+				Compression: "gzip",
+				StorageTargets: []StorageTargetConfig{{
+					ID: 11, Name: "master-disk", Type: storage.TypeLocalDisk, TransferMode: storage.TransferModeMasterRelay,
+				}},
+			})
+		case r.Method == http.MethodPut && r.URL.Path == "/api/agent/records/99/artifacts/11":
+			body, err := io.ReadAll(r.Body)
+			if err != nil {
+				t.Fatalf("ReadAll relayed body: %v", err)
+			}
+			digest := sha256.Sum256(body)
+			if got := r.Header.Get("X-BackupX-SHA256"); got != fmt.Sprintf("%x", digest[:]) {
+				t.Fatalf("relay checksum header = %q", got)
+			}
+			if r.Header.Get("X-BackupX-Object-Key") == "" || r.ContentLength != int64(len(body)) {
+				t.Fatalf("invalid relay metadata: key=%q length=%d body=%d", r.Header.Get("X-BackupX-Object-Key"), r.ContentLength, len(body))
+			}
+			relayed = append([]byte(nil), body...)
+			writeAgentEnvelope(t, w, map[string]string{"status": "ok"})
+		case r.Method == http.MethodPost && r.URL.Path == "/api/agent/records/99":
+			var update RecordUpdate
+			if err := json.NewDecoder(r.Body).Decode(&update); err != nil {
+				t.Fatalf("Decode update returned error: %v", err)
+			}
+			if update.Status != "" {
+				finalUpdate = update
+			}
+			writeAgentEnvelope(t, w, map[string]string{"status": "ok"})
+		default:
+			http.NotFound(w, r)
+		}
+	}))
+	defer server.Close()
+
+	executor := NewExecutor(NewMasterClient(server.URL, "token", false), filepath.Join(t.TempDir(), "tmp"))
+	if err := executor.ExecuteRunTask(context.Background(), 1, 99); err != nil {
+		t.Fatalf("ExecuteRunTask returned error: %v", err)
+	}
+	if len(relayed) == 0 {
+		t.Fatal("expected artifact bytes to be streamed through Master")
+	}
+	if finalUpdate.Status != "success" || finalUpdate.StorageTransferMode != storage.TransferModeMasterRelay {
+		t.Fatalf("unexpected final relay update: %#v", finalUpdate)
+	}
+	if len(finalUpdate.StorageUploadResults) != 1 || finalUpdate.StorageUploadResults[0].TransferMode != storage.TransferModeMasterRelay {
+		t.Fatalf("unexpected relay target result: %#v", finalUpdate.StorageUploadResults)
+	}
+}
+
+func TestExecuteRestoreDownloadsMasterRelayedArtifact(t *testing.T) {
+	var archive bytes.Buffer
+	tarWriter := tar.NewWriter(&archive)
+	content := []byte("restored through Master")
+	header := &tar.Header{Name: "site/index.html", Mode: 0o644, Size: int64(len(content)), Typeflag: tar.TypeReg}
+	if err := tarWriter.WriteHeader(header); err != nil {
+		t.Fatalf("WriteHeader returned error: %v", err)
+	}
+	if _, err := tarWriter.Write(content); err != nil {
+		t.Fatalf("Write returned error: %v", err)
+	}
+	if err := tarWriter.Close(); err != nil {
+		t.Fatalf("Close returned error: %v", err)
+	}
+	artifact := append([]byte(nil), archive.Bytes()...)
+	digest := sha256.Sum256(artifact)
+	restoreRoot := t.TempDir()
+	restoreSource := filepath.Join(restoreRoot, "site")
+	artifactRequests := 0
+	var finalUpdate RestoreUpdate
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch {
+		case r.Method == http.MethodGet && r.URL.Path == "/api/agent/restores/77/spec":
+			writeAgentEnvelope(t, w, RestoreSpec{
+				RestoreRecordID: 77,
+				BackupRecordID:  99,
+				TaskID:          1,
+				TaskName:        "remote-source",
+				Type:            "file",
+				SourcePath:      restoreSource,
+				Storage: StorageTargetConfig{
+					ID: 11, Name: "master-disk", Type: storage.TypeLocalDisk, TransferMode: storage.TransferModeMasterRelay,
+				},
+				StoragePath: "BackupX/file/site.tar",
+				FileName:    "site.tar",
+				Checksum:    fmt.Sprintf("%x", digest[:]),
+			})
+		case r.Method == http.MethodGet && r.URL.Path == "/api/agent/restores/77/artifact":
+			artifactRequests++
+			if r.Header.Get("X-Agent-Token") != "token" {
+				t.Fatalf("missing Agent token on relay download")
+			}
+			w.Header().Set("Content-Length", fmt.Sprintf("%d", len(artifact)))
+			_, _ = w.Write(artifact)
+		case r.Method == http.MethodPost && r.URL.Path == "/api/agent/restores/77":
+			var update RestoreUpdate
+			if err := json.NewDecoder(r.Body).Decode(&update); err != nil {
+				t.Fatalf("Decode update returned error: %v", err)
+			}
+			if update.Status != "" {
+				finalUpdate = update
+			}
+			writeAgentEnvelope(t, w, map[string]string{"status": "ok"})
+		default:
+			http.NotFound(w, r)
+		}
+	}))
+	defer server.Close()
+
+	executor := NewExecutor(NewMasterClient(server.URL, "token", false), filepath.Join(t.TempDir(), "tmp"))
+	if err := executor.ExecuteRestore(context.Background(), 77); err != nil {
+		t.Fatalf("ExecuteRestore returned error: %v", err)
+	}
+	if artifactRequests != 1 {
+		t.Fatalf("expected one relay artifact request, got %d", artifactRequests)
+	}
+	restored, err := os.ReadFile(filepath.Join(restoreRoot, "site", "index.html"))
+	if err != nil {
+		t.Fatalf("ReadFile returned error: %v", err)
+	}
+	if string(restored) != string(content) {
+		t.Fatalf("restored content = %q, want %q", restored, content)
+	}
+	if finalUpdate.Status != "success" {
+		t.Fatalf("unexpected final restore update: %#v", finalUpdate)
+	}
+}
+
 func TestExecuteRunTaskReportsPerTargetUploadResultsWhenAllTargetsFail(t *testing.T) {
 	sourceDir := t.TempDir()
 	if err := os.WriteFile(filepath.Join(sourceDir, "index.html"), []byte("hello"), 0o644); err != nil {

server/internal/app/app.go

@@ -135,7 +135,7 @@ func New(ctx context.Context, cfg config.Config, version string) (*Application,
 	// Agent 协议服务：命令队列 + 任务下发 + 记录上报
 	agentCmdRepo := repository.NewAgentCommandRepository(db)
 	nodeService.SetAgentCommandRepository(agentCmdRepo)
-	agentService := service.NewAgentService(nodeRepo, backupTaskRepo, backupRecordRepo, storageTargetRepo, agentCmdRepo, configCipher)
+	agentService := service.NewAgentService(nodeRepo, backupTaskRepo, backupRecordRepo, storageTargetRepo, agentCmdRepo, configCipher, storageRegistry)
 	agentService.SetRestoreRepository(restoreRecordRepo)
 	agentService.StartCommandTimeoutMonitor(ctx, 30*time.Second, 10*time.Minute)
 

server/internal/http/agent_handler.go

@@ -156,6 +156,44 @@ func (h *AgentHandler) UpdateRecord(c *gin.Context) {
 	response.Success(c, gin.H{"status": "ok"})
 }
 
+// UploadArtifact streams a remote source artifact into storage mounted only on
+// the Master. The request body is never buffered as a whole in memory or disk.
+func (h *AgentHandler) UploadArtifact(c *gin.Context) {
+	node, err := h.agentService.AuthenticatedNode(c.Request.Context(), extractToken(c))
+	if err != nil {
+		response.Error(c, err)
+		return
+	}
+	recordID, err := strconv.ParseUint(c.Param("id"), 10, 32)
+	if err != nil {
+		response.Error(c, err)
+		return
+	}
+	targetID, err := strconv.ParseUint(c.Param("targetId"), 10, 32)
+	if err != nil {
+		response.Error(c, err)
+		return
+	}
+	if c.Request.ContentLength < 0 {
+		c.JSON(stdhttp.StatusLengthRequired, gin.H{"code": "CONTENT_LENGTH_REQUIRED", "message": "artifact content length is required"})
+		return
+	}
+	if err := h.agentService.UploadArtifact(
+		c.Request.Context(),
+		node,
+		uint(recordID),
+		uint(targetID),
+		c.GetHeader("X-BackupX-Object-Key"),
+		c.Request.ContentLength,
+		c.GetHeader("X-BackupX-SHA256"),
+		c.Request.Body,
+	); err != nil {
+		response.Error(c, err)
+		return
+	}
+	response.Success(c, gin.H{"status": "ok"})
+}
+
 // GetRestoreSpec Agent 拉取恢复规格。
 func (h *AgentHandler) GetRestoreSpec(c *gin.Context) {
 	if h.restoreService == nil {
@@ -208,6 +246,34 @@ func (h *AgentHandler) UpdateRestore(c *gin.Context) {
 	response.Success(c, gin.H{"status": "ok"})
 }
 
+// DownloadRestoreArtifact streams a Master-local backup back to its source
+// Agent for restore without exposing the local storage configuration.
+func (h *AgentHandler) DownloadRestoreArtifact(c *gin.Context) {
+	if h.restoreService == nil {
+		c.JSON(stdhttp.StatusServiceUnavailable, gin.H{"code": "RESTORE_SERVICE_DISABLED", "message": "restore service is not enabled"})
+		return
+	}
+	node, err := h.agentService.AuthenticatedNode(c.Request.Context(), extractToken(c))
+	if err != nil {
+		response.Error(c, err)
+		return
+	}
+	restoreID, err := strconv.ParseUint(c.Param("id"), 10, 32)
+	if err != nil {
+		response.Error(c, err)
+		return
+	}
+	artifact, err := h.restoreService.DownloadAgentArtifact(c.Request.Context(), node, uint(restoreID))
+	if err != nil {
+		response.Error(c, err)
+		return
+	}
+	c.DataFromReader(stdhttp.StatusOK, artifact.Size, "application/octet-stream", artifact.Reader, nil)
+	if err := artifact.Reader.Close(); err != nil {
+		_ = c.Error(err)
+	}
+}
+
 // Self 返回当前 Agent token 所属节点的状态，供安装脚本末尾探活。
 func (h *AgentHandler) Self(c *gin.Context) {
 	node, err := h.agentService.AuthenticatedNode(c.Request.Context(), extractToken(c))

server/internal/http/router.go

@@ -322,7 +322,9 @@ func NewRouter(deps RouterDependencies) *gin.Engine {
 			agent.POST("/commands/:id/result", agentHandler.SubmitCommandResult)
 			agent.GET("/tasks/:id", agentHandler.GetTaskSpec)
 			agent.POST("/records/:id", agentHandler.UpdateRecord)
+			agent.PUT("/records/:id/artifacts/:targetId", agentHandler.UploadArtifact)
 			agent.GET("/restores/:id/spec", agentHandler.GetRestoreSpec)
+			agent.GET("/restores/:id/artifact", agentHandler.DownloadRestoreArtifact)
 			agent.POST("/restores/:id", agentHandler.UpdateRestore)
 
 			// Agent v1（安装脚本探活用），仅 Self 端点

server/internal/model/backup_record.go

@@ -22,14 +22,16 @@ type BackupRecord struct {
 	Task            BackupTask    `json:"task,omitempty"`
 	StorageTargetID uint          `gorm:"column:storage_target_id;index;not null" json:"storageTargetId"`
 	StorageTarget   StorageTarget `json:"storageTarget,omitempty"`
-	// NodeID 执行该次备份的节点（0 = 本机 Master）。用于集群中识别 local_disk 类型
-	// 存储的归属节点，避免 Master 端试图跨节点访问远程 Agent 的本地存储。
-	NodeID               uint   `gorm:"column:node_id;index;default:0" json:"nodeId"`
-	Status               string `gorm:"size:20;index;not null" json:"status"`
-	FileName             string `gorm:"column:file_name;size:255" json:"fileName"`
-	FileSize             int64  `gorm:"column:file_size;not null;default:0" json:"fileSize"`
-	Checksum             string `gorm:"column:checksum;size:64" json:"checksum"`
-	StoragePath          string `gorm:"column:storage_path;size:500" json:"storagePath"`
+	// NodeID 执行该次备份的节点（0 = 本机 Master）。StorageTransferMode 进一步
+	// 区分远程 Agent 直写与 Master 中转，避免在错误节点访问 local_disk。
+	NodeID      uint   `gorm:"column:node_id;index;default:0" json:"nodeId"`
+	Status      string `gorm:"size:20;index;not null" json:"status"`
+	FileName    string `gorm:"column:file_name;size:255" json:"fileName"`
+	FileSize    int64  `gorm:"column:file_size;not null;default:0" json:"fileSize"`
+	Checksum    string `gorm:"column:checksum;size:64" json:"checksum"`
+	StoragePath string `gorm:"column:storage_path;size:500" json:"storagePath"`
+	// 空值表示旧版 Agent 直写；direct / master_relay 记录新协议的实际数据路径。
+	StorageTransferMode  string `gorm:"column:storage_transfer_mode;size:20" json:"storageTransferMode,omitempty"`
 	StorageUploadResults string `gorm:"column:storage_upload_results;type:text" json:"-"`
 	DurationSeconds      int    `gorm:"column:duration_seconds;not null;default:0" json:"durationSeconds"`
 	// Locked 保留锁定（法律保留）：为 true 时该备份不参与保留期/数量自动清理，

server/internal/service/agent_service.go

@@ -2,15 +2,19 @@ package service
 
 import (
 	"context"
+	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
+	"path"
 	"strings"
 	"time"
 
 	"backupx/server/internal/apperror"
 	"backupx/server/internal/model"
 	"backupx/server/internal/repository"
+	"backupx/server/internal/storage"
 	"backupx/server/internal/storage/codec"
 )
 
@@ -23,6 +27,7 @@ type AgentService struct {
 	storageRepo repository.StorageTargetRepository
 	cmdRepo     repository.AgentCommandRepository
 	restoreRepo repository.RestoreRecordRepository
+	registry    *storage.Registry
 	cipher      *codec.ConfigCipher
 }
 
@@ -33,6 +38,7 @@ func NewAgentService(
 	storageRepo repository.StorageTargetRepository,
 	cmdRepo repository.AgentCommandRepository,
 	cipher *codec.ConfigCipher,
+	registry *storage.Registry,
 ) *AgentService {
 	return &AgentService{
 		nodeRepo:    nodeRepo,
@@ -40,6 +46,7 @@ func NewAgentService(
 		recordRepo:  recordRepo,
 		storageRepo: storageRepo,
 		cmdRepo:     cmdRepo,
+		registry:    registry,
 		cipher:      cipher,
 	}
 }
@@ -145,10 +152,11 @@ type AgentTaskSpec struct {
 
 // AgentStorageTargetConfig 存储目标配置（已解密）
 type AgentStorageTargetConfig struct {
-	ID     uint            `json:"id"`
-	Type   string          `json:"type"`
-	Name   string          `json:"name"`
-	Config json.RawMessage `json:"config"`
+	ID           uint            `json:"id"`
+	Type         string          `json:"type"`
+	Name         string          `json:"name"`
+	Config       json.RawMessage `json:"config"`
+	TransferMode string          `json:"transferMode"`
 }
 
 // GetTaskSpec 返回 Agent 执行任务所需的完整规格。
@@ -187,11 +195,22 @@ func (s *AgentService) GetTaskSpec(ctx context.Context, node *model.Node, taskID
 		if err != nil {
 			return nil, fmt.Errorf("decrypt storage config: %w", err)
 		}
+		transferMode := storage.TransferModeDirect
+		if strings.EqualFold(target.Type, storage.TypeLocalDisk) {
+			var localConfig storage.LocalDiskConfig
+			if err := json.Unmarshal(configRaw, &localConfig); err != nil {
+				return nil, fmt.Errorf("decode local disk config: %w", err)
+			}
+			if localConfig.MasterRelay {
+				transferMode = storage.TransferModeMasterRelay
+			}
+		}
 		storageTargets = append(storageTargets, AgentStorageTargetConfig{
-			ID:     target.ID,
-			Type:   target.Type,
-			Name:   target.Name,
-			Config: json.RawMessage(configRaw),
+			ID:           target.ID,
+			Type:         target.Type,
+			Name:         target.Name,
+			Config:       json.RawMessage(configRaw),
+			TransferMode: transferMode,
 		})
 	}
 	return &AgentTaskSpec{
@@ -214,6 +233,101 @@ func (s *AgentService) GetTaskSpec(ctx context.Context, node *model.Node, taskID
 	}, nil
 }
 
+// UploadArtifact receives a remote Agent artifact as a stream and writes it
+// with a provider created on the Master. The first supported use is local_disk,
+// whose configured path belongs to the Master rather than the source Agent.
+func (s *AgentService) UploadArtifact(ctx context.Context, node *model.Node, recordID, targetID uint, objectKey string, size int64, checksum string, reader io.Reader) error {
+	if node == nil || reader == nil || s.registry == nil {
+		return apperror.BadRequest("AGENT_ARTIFACT_INVALID", "中转上传参数不完整", nil)
+	}
+	record, err := s.recordRepo.FindByID(ctx, recordID)
+	if err != nil {
+		return err
+	}
+	if record == nil {
+		return apperror.New(404, "BACKUP_RECORD_NOT_FOUND", "记录不存在", nil)
+	}
+	task, err := s.taskRepo.FindByID(ctx, record.TaskID)
+	if err != nil {
+		return err
+	}
+	if task == nil || !recordBelongsToNode(record, task, node.ID) {
+		return apperror.Unauthorized("BACKUP_RECORD_FORBIDDEN", "记录不属于当前节点", nil)
+	}
+	if isBackupRecordTerminal(record.Status) {
+		return apperror.BadRequest("BACKUP_RECORD_TERMINAL", "备份记录已结束，不能继续上传产物", nil)
+	}
+	allowedTarget := false
+	for _, configuredTargetID := range collectTargetIDs(task) {
+		if configuredTargetID == targetID {
+			allowedTarget = true
+			break
+		}
+	}
+	if !allowedTarget {
+		return apperror.Unauthorized("BACKUP_STORAGE_TARGET_FORBIDDEN", "存储目标不属于该任务", nil)
+	}
+	target, err := s.storageRepo.FindByID(ctx, targetID)
+	if err != nil {
+		return err
+	}
+	if target == nil || !strings.EqualFold(target.Type, storage.TypeLocalDisk) {
+		return apperror.BadRequest("AGENT_ARTIFACT_RELAY_UNSUPPORTED", "仅 Master 本地磁盘目标需要中转上传", nil)
+	}
+	configMap := map[string]any{}
+	if err := s.cipher.DecryptJSON(target.ConfigCiphertext, &configMap); err != nil {
+		return fmt.Errorf("decrypt storage config: %w", err)
+	}
+	masterRelay, _ := configMap["masterRelay"].(bool)
+	if !masterRelay {
+		return apperror.BadRequest("AGENT_ARTIFACT_RELAY_UNSUPPORTED", "该本地磁盘目标配置为 Agent 直接写入", nil)
+	}
+	cleanKey := path.Clean(strings.TrimSpace(objectKey))
+	if cleanKey == "." || path.IsAbs(cleanKey) || strings.HasPrefix(cleanKey, "../") || cleanKey != objectKey || strings.Contains(objectKey, "\\") {
+		return apperror.BadRequest("AGENT_ARTIFACT_INVALID_PATH", "中转上传对象路径不安全", nil)
+	}
+	checksumBytes, checksumErr := hex.DecodeString(strings.TrimSpace(checksum))
+	if size < 0 || checksumErr != nil || len(checksumBytes) != 32 {
+		return apperror.BadRequest("AGENT_ARTIFACT_INVALID", "中转上传需要有效的大小和 SHA-256", checksumErr)
+	}
+	if target.QuotaBytes > 0 {
+		usage, usageErr := s.recordRepo.StorageUsage(ctx)
+		if usageErr != nil {
+			return fmt.Errorf("read storage usage: %w", usageErr)
+		}
+		currentUsed := int64(0)
+		for _, item := range usage {
+			if item.StorageTargetID == targetID {
+				currentUsed = item.TotalSize
+				break
+			}
+		}
+		if currentUsed+size > target.QuotaBytes {
+			return apperror.BadRequest("BACKUP_STORAGE_QUOTA_EXCEEDED", fmt.Sprintf("超出存储目标配额（%d + %d > %d）", currentUsed, size, target.QuotaBytes), nil)
+		}
+	}
+	provider, err := s.registry.Create(ctx, target.Type, configMap)
+	if err != nil {
+		return fmt.Errorf("create master relay provider: %w", err)
+	}
+	limited := io.LimitReader(reader, size+1)
+	hashed := newHashingReader(limited)
+	metadata := map[string]string{
+		"taskId":       fmt.Sprintf("%d", task.ID),
+		"recordId":     fmt.Sprintf("%d", record.ID),
+		"sourceNodeId": fmt.Sprintf("%d", node.ID),
+		"transferMode": storage.TransferModeMasterRelay,
+	}
+	if err := provider.Upload(ctx, cleanKey, hashed, size, metadata); err != nil {
+		return errors.Join(fmt.Errorf("relay artifact to master storage: %w", err), provider.Delete(ctx, cleanKey))
+	}
+	if hashed.n != size || !strings.EqualFold(hashed.Sum(), checksum) {
+		deleteErr := provider.Delete(ctx, cleanKey)
+		return errors.Join(fmt.Errorf("relayed artifact integrity mismatch: received %d of %d bytes", hashed.n, size), deleteErr)
+	}
+	return nil
+}
+
 func (s *AgentService) ensureTaskSpecAccess(ctx context.Context, node *model.Node, task *model.BackupTask) error {
 	if task.NodeID == node.ID {
 		return nil
@@ -236,6 +350,7 @@ type AgentRecordUpdate struct {
 	Checksum             string                    `json:"checksum,omitempty"`
 	StoragePath          string                    `json:"storagePath,omitempty"`
 	StorageTargetID      uint                      `json:"storageTargetId,omitempty"`
+	StorageTransferMode  string                    `json:"storageTransferMode,omitempty"`
 	StorageUploadResults []StorageUploadResultItem `json:"storageUploadResults,omitempty"`
 	ErrorMessage         string                    `json:"errorMessage,omitempty"`
 	LogAppend            string                    `json:"logAppend,omitempty"` // 增量日志，追加到 record.log_content
@@ -260,6 +375,60 @@ func (s *AgentService) UpdateRecord(ctx context.Context, node *model.Node, recor
 	if isBackupRecordTerminal(record.Status) {
 		return nil
 	}
+	allowedTargets := make(map[uint]struct{})
+	for _, targetID := range collectTargetIDs(task) {
+		allowedTargets[targetID] = struct{}{}
+	}
+	targetCache := make(map[uint]*model.StorageTarget)
+	validateTransferMode := func(targetID uint, transferMode string) error {
+		if _, ok := allowedTargets[targetID]; !ok {
+			return apperror.Unauthorized("BACKUP_STORAGE_TARGET_FORBIDDEN", "存储目标不属于该任务", nil)
+		}
+		if transferMode == "" {
+			return nil
+		}
+		target := targetCache[targetID]
+		if target == nil {
+			var findErr error
+			target, findErr = s.storageRepo.FindByID(ctx, targetID)
+			if findErr != nil {
+				return findErr
+			}
+			if target == nil {
+				return apperror.BadRequest("BACKUP_STORAGE_TARGET_INVALID", "存储目标不存在", nil)
+			}
+			targetCache[targetID] = target
+		}
+		expectedMode := storage.TransferModeDirect
+		if strings.EqualFold(target.Type, storage.TypeLocalDisk) {
+			var localConfig storage.LocalDiskConfig
+			if err := s.cipher.DecryptJSON(target.ConfigCiphertext, &localConfig); err != nil {
+				return fmt.Errorf("decrypt storage config: %w", err)
+			}
+			if localConfig.MasterRelay {
+				expectedMode = storage.TransferModeMasterRelay
+			}
+		}
+		if transferMode != expectedMode {
+			return apperror.BadRequest("AGENT_STORAGE_TRANSFER_MODE_INVALID", "Agent 上报的存储传输模式与目标配置不一致", nil)
+		}
+		return nil
+	}
+	if update.StorageTargetID > 0 {
+		if _, ok := allowedTargets[update.StorageTargetID]; !ok {
+			return apperror.Unauthorized("BACKUP_STORAGE_TARGET_FORBIDDEN", "存储目标不属于该任务", nil)
+		}
+		if err := validateTransferMode(update.StorageTargetID, update.StorageTransferMode); err != nil {
+			return err
+		}
+	} else if update.StorageTransferMode != "" {
+		return apperror.BadRequest("AGENT_STORAGE_TRANSFER_MODE_INVALID", "传输模式缺少对应的存储目标", nil)
+	}
+	for _, result := range update.StorageUploadResults {
+		if err := validateTransferMode(result.StorageTargetID, result.TransferMode); err != nil {
+			return err
+		}
+	}
 	if update.Status != "" {
 		record.Status = update.Status
 	}
@@ -278,6 +447,9 @@ func (s *AgentService) UpdateRecord(ctx context.Context, node *model.Node, recor
 	if update.StorageTargetID > 0 {
 		record.StorageTargetID = update.StorageTargetID
 	}
+	if update.StorageTransferMode != "" {
+		record.StorageTransferMode = update.StorageTransferMode
+	}
 	if len(update.StorageUploadResults) > 0 {
 		if resultsJSON, marshalErr := json.Marshal(update.StorageUploadResults); marshalErr == nil {
 			record.StorageUploadResults = string(resultsJSON)

server/internal/service/agent_service_test.go

@@ -1,8 +1,12 @@
 package service
 
 import (
+	"bytes"
 	"context"
+	"crypto/sha256"
 	"errors"
+	"fmt"
+	"os"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -13,7 +17,9 @@ import (
 	"backupx/server/internal/logger"
 	"backupx/server/internal/model"
 	"backupx/server/internal/repository"
+	"backupx/server/internal/storage"
 	"backupx/server/internal/storage/codec"
+	storageRclone "backupx/server/internal/storage/rclone"
 	"gorm.io/gorm"
 )
 
@@ -42,7 +48,7 @@ func newAgentServicePoolTestHarness(t *testing.T) (*AgentService, *gorm.DB, repo
 	if err := nodeRepo.Create(context.Background(), other); err != nil {
 		t.Fatalf("create other node: %v", err)
 	}
-	targetConfig, err := cipher.EncryptJSON(map[string]any{"basePath": t.TempDir()})
+	targetConfig, err := cipher.EncryptJSON(map[string]any{"basePath": t.TempDir(), "masterRelay": true})
 	if err != nil {
 		t.Fatalf("EncryptJSON returned error: %v", err)
 	}
@@ -76,7 +82,8 @@ func newAgentServicePoolTestHarness(t *testing.T) (*AgentService, *gorm.DB, repo
 	if err := recordRepo.Create(context.Background(), record); err != nil {
 		t.Fatalf("create record: %v", err)
 	}
-	return NewAgentService(nodeRepo, taskRepo, recordRepo, storageRepo, cmdRepo, cipher), db, recordRepo, cmdRepo, owner, other
+	storageRegistry := storage.NewRegistry(storageRclone.NewLocalDiskFactory())
+	return NewAgentService(nodeRepo, taskRepo, recordRepo, storageRepo, cmdRepo, cipher, storageRegistry), db, recordRepo, cmdRepo, owner, other
 }
 
 func TestAgentServicePooledTaskUsesRecordNodeForSpecAndRecordUpdates(t *testing.T) {
@@ -90,19 +97,22 @@ func TestAgentServicePooledTaskUsesRecordNodeForSpecAndRecordUpdates(t *testing.
 	if spec.TaskID != 1 || len(spec.StorageTargets) != 1 {
 		t.Fatalf("unexpected spec: %#v", spec)
 	}
+	if spec.StorageTargets[0].TransferMode != storage.TransferModeMasterRelay {
+		t.Fatalf("expected local disk to use Master relay, got %#v", spec.StorageTargets[0])
+	}
 	if _, err := svc.GetTaskSpec(ctx, other, 1); err == nil {
 		t.Fatal("expected non-owner node to be forbidden from pooled task spec")
 	}
 
 	if err := svc.UpdateRecord(ctx, owner, 1, AgentRecordUpdate{
-		Status:          model.BackupRecordStatusSuccess,
-		FileName:        "backup.tar.gz",
-		FileSize:        123,
-		StoragePath:     "tasks/1/backup.tar.gz",
-		StorageTargetID: 2,
+		Status:              model.BackupRecordStatusSuccess,
+		FileName:            "backup.tar.gz",
+		FileSize:            123,
+		StoragePath:         "tasks/1/backup.tar.gz",
+		StorageTargetID:     1,
+		StorageTransferMode: storage.TransferModeMasterRelay,
 		StorageUploadResults: []StorageUploadResultItem{
-			{StorageTargetID: 1, StorageTargetName: "first", Status: "failed", Error: "boom"},
-			{StorageTargetID: 2, StorageTargetName: "second", Status: "success", StoragePath: "tasks/1/backup.tar.gz", FileSize: 123},
+			{StorageTargetID: 1, StorageTargetName: "local", Status: "success", StoragePath: "tasks/1/backup.tar.gz", FileSize: 123, TransferMode: storage.TransferModeMasterRelay},
 		},
 	}); err != nil {
 		t.Fatalf("owner UpdateRecord returned error: %v", err)
@@ -114,10 +124,13 @@ func TestAgentServicePooledTaskUsesRecordNodeForSpecAndRecordUpdates(t *testing.
 	if updated.Status != model.BackupRecordStatusSuccess || updated.NodeID != owner.ID {
 		t.Fatalf("unexpected updated record: %#v", updated)
 	}
-	if updated.StorageTargetID != 2 {
-		t.Fatalf("expected successful storage target id 2, got %d", updated.StorageTargetID)
+	if updated.StorageTargetID != 1 {
+		t.Fatalf("expected successful storage target id 1, got %d", updated.StorageTargetID)
 	}
-	if !strings.Contains(updated.StorageUploadResults, `"storageTargetName":"second"`) {
+	if updated.StorageTransferMode != storage.TransferModeMasterRelay {
+		t.Fatalf("expected Master relay transfer mode, got %q", updated.StorageTransferMode)
+	}
+	if !strings.Contains(updated.StorageUploadResults, `"storageTargetName":"local"`) {
 		t.Fatalf("expected upload results to be persisted, got %q", updated.StorageUploadResults)
 	}
 	if err := svc.UpdateRecord(ctx, other, 1, AgentRecordUpdate{LogAppend: "bad"}); err == nil {
@@ -125,6 +138,69 @@ func TestAgentServicePooledTaskUsesRecordNodeForSpecAndRecordUpdates(t *testing.
 	}
 }
 
+func TestAgentServiceRelaysRemoteArtifactToMasterLocalDisk(t *testing.T) {
+	svc, _, _, _, owner, other := newAgentServicePoolTestHarness(t)
+	ctx := context.Background()
+	payload := []byte("artifact from remote source server")
+	digest := sha256.Sum256(payload)
+	checksum := fmt.Sprintf("%x", digest[:])
+	objectKey := "file/2026/08/06/remote-source.tar"
+
+	if err := svc.UploadArtifact(ctx, owner, 1, 1, objectKey, int64(len(payload)), checksum, bytes.NewReader(payload)); err != nil {
+		t.Fatalf("UploadArtifact returned error: %v", err)
+	}
+	target, err := svc.storageRepo.FindByID(ctx, 1)
+	if err != nil || target == nil {
+		t.Fatalf("FindByID target: target=%#v err=%v", target, err)
+	}
+	config := map[string]any{}
+	if err := svc.cipher.DecryptJSON(target.ConfigCiphertext, &config); err != nil {
+		t.Fatalf("DecryptJSON target config: %v", err)
+	}
+	basePath, _ := config["basePath"].(string)
+	stored, err := os.ReadFile(filepath.Join(basePath, filepath.FromSlash(objectKey)))
+	if err != nil {
+		t.Fatalf("read relayed artifact: %v", err)
+	}
+	if !bytes.Equal(stored, payload) {
+		t.Fatalf("relayed artifact differs: got %q", stored)
+	}
+	if err := svc.UploadArtifact(ctx, other, 1, 1, "file/forbidden.tar", int64(len(payload)), checksum, bytes.NewReader(payload)); err == nil {
+		t.Fatal("expected a different node to be forbidden from relaying the artifact")
+	}
+}
+
+func TestAgentServiceKeepsExistingLocalDiskTargetsAgentLocal(t *testing.T) {
+	svc, _, _, _, owner, _ := newAgentServicePoolTestHarness(t)
+	ctx := context.Background()
+	target, err := svc.storageRepo.FindByID(ctx, 1)
+	if err != nil || target == nil {
+		t.Fatalf("FindByID target: target=%#v err=%v", target, err)
+	}
+	legacyConfig, err := svc.cipher.EncryptJSON(map[string]any{"basePath": t.TempDir()})
+	if err != nil {
+		t.Fatalf("EncryptJSON legacy target: %v", err)
+	}
+	target.ConfigCiphertext = legacyConfig
+	if err := svc.storageRepo.Update(ctx, target); err != nil {
+		t.Fatalf("Update legacy target: %v", err)
+	}
+
+	spec, err := svc.GetTaskSpec(ctx, owner, 1)
+	if err != nil {
+		t.Fatalf("GetTaskSpec returned error: %v", err)
+	}
+	if len(spec.StorageTargets) != 1 || spec.StorageTargets[0].TransferMode != storage.TransferModeDirect {
+		t.Fatalf("expected legacy local disk to stay Agent-local, got %#v", spec.StorageTargets)
+	}
+	payload := []byte("must not be relayed")
+	digest := sha256.Sum256(payload)
+	err = svc.UploadArtifact(ctx, owner, 1, 1, "file/legacy.tar", int64(len(payload)), fmt.Sprintf("%x", digest[:]), bytes.NewReader(payload))
+	if err == nil {
+		t.Fatal("expected relay upload to be rejected for an Agent-local target")
+	}
+}
+
 func TestAgentServiceUpdateRecordRefreshesTaskSummaryOnTerminalStatus(t *testing.T) {
 	for _, status := range []string{model.BackupRecordStatusSuccess, model.BackupRecordStatusFailed} {
 		t.Run(status, func(t *testing.T) {

server/internal/service/backup_execution_service.go

@@ -51,6 +51,7 @@ type StorageUploadResultItem struct {
 	Status            string `json:"status"`
 	StoragePath       string `json:"storagePath,omitempty"`
 	FileSize          int64  `json:"fileSize,omitempty"`
+	TransferMode      string `json:"transferMode,omitempty"`
 	Error             string `json:"error,omitempty"`
 }
 
@@ -410,6 +411,9 @@ func (s *BackupExecutionService) deleteRemoteLocalDiskObject(ctx context.Context
 	if strings.TrimSpace(record.StoragePath) == "" || s.nodeRepo == nil {
 		return false, nil
 	}
+	if record.StorageTransferMode == storage.TransferModeMasterRelay {
+		return false, nil
+	}
 	node, err := s.nodeRepo.FindByID(ctx, record.NodeID)
 	if err != nil || node == nil || node.IsLocal {
 		return false, nil

server/internal/service/backup_execution_service_test.go

@@ -429,6 +429,56 @@ func TestBackupExecutionServiceRestoreRecordRejectsRemoteLocalDisk(t *testing.T)
 	}
 }
 
+func TestBackupExecutionServiceDownloadsMasterRelayedLocalDiskRecord(t *testing.T) {
+	executionService, _, tasks, _, records, _, storageDir := newExecutionTestServices(t)
+	ctx := context.Background()
+	executionService.SetClusterDependencies(&nodeRepoStub{nodes: []model.Node{
+		{ID: 10, Name: "edge-a", Token: "edge-a-token", Status: model.NodeStatusOnline},
+	}}, &fakeDispatcher{})
+	task, err := tasks.FindByID(ctx, 1)
+	if err != nil {
+		t.Fatalf("FindByID task returned error: %v", err)
+	}
+	storagePath := "file/2026/05/09/relayed.tar"
+	artifactPath := filepath.Join(storageDir, filepath.FromSlash(storagePath))
+	if err := os.MkdirAll(filepath.Dir(artifactPath), 0o755); err != nil {
+		t.Fatalf("MkdirAll artifact parent returned error: %v", err)
+	}
+	content := []byte("stored on Master")
+	if err := os.WriteFile(artifactPath, content, 0o600); err != nil {
+		t.Fatalf("WriteFile artifact returned error: %v", err)
+	}
+	completedAt := time.Now().UTC()
+	record := &model.BackupRecord{
+		TaskID:              task.ID,
+		StorageTargetID:     task.StorageTargetID,
+		NodeID:              10,
+		Status:              model.BackupRecordStatusSuccess,
+		FileName:            "relayed.tar",
+		FileSize:            int64(len(content)),
+		StoragePath:         storagePath,
+		StorageTransferMode: storage.TransferModeMasterRelay,
+		StartedAt:           completedAt.Add(-time.Second),
+		CompletedAt:         &completedAt,
+	}
+	if err := records.Create(ctx, record); err != nil {
+		t.Fatalf("Create record returned error: %v", err)
+	}
+
+	download, err := executionService.DownloadRecord(ctx, record.ID)
+	if err != nil {
+		t.Fatalf("DownloadRecord returned error: %v", err)
+	}
+	got, readErr := io.ReadAll(download.Reader)
+	closeErr := download.Reader.Close()
+	if readErr != nil || closeErr != nil {
+		t.Fatalf("read relayed artifact: read=%v close=%v", readErr, closeErr)
+	}
+	if !bytes.Equal(got, content) {
+		t.Fatalf("downloaded content = %q, want %q", got, content)
+	}
+}
+
 func TestBackupExecutionServiceRecordsFirstSuccessfulStorageTarget(t *testing.T) {
 	executionService, _, tasks, targets, records, _, _ := newExecutionTestServices(t)
 	ctx := context.Background()

server/internal/service/backup_record_service.go

@@ -23,22 +23,23 @@ type BackupRecordListInput struct {
 }
 
 type BackupRecordSummary struct {
-	ID                uint       `json:"id"`
-	TaskID            uint       `json:"taskId"`
-	TaskName          string     `json:"taskName"`
-	StorageTargetID   uint       `json:"storageTargetId"`
-	StorageTargetName string     `json:"storageTargetName"`
-	Status            string     `json:"status"`
-	FileName          string     `json:"fileName"`
-	FileSize          int64      `json:"fileSize"`
-	Checksum          string     `json:"checksum"`
-	StoragePath       string     `json:"storagePath"`
-	DurationSeconds   int        `json:"durationSeconds"`
-	ErrorMessage      string     `json:"errorMessage"`
-	StartedAt         time.Time  `json:"startedAt"`
-	CompletedAt       *time.Time `json:"completedAt,omitempty"`
-	Locked            bool       `json:"locked"`
-	BackupKind        string     `json:"backupKind"`
+	ID                  uint       `json:"id"`
+	TaskID              uint       `json:"taskId"`
+	TaskName            string     `json:"taskName"`
+	StorageTargetID     uint       `json:"storageTargetId"`
+	StorageTargetName   string     `json:"storageTargetName"`
+	Status              string     `json:"status"`
+	FileName            string     `json:"fileName"`
+	FileSize            int64      `json:"fileSize"`
+	Checksum            string     `json:"checksum"`
+	StoragePath         string     `json:"storagePath"`
+	StorageTransferMode string     `json:"storageTransferMode,omitempty"`
+	DurationSeconds     int        `json:"durationSeconds"`
+	ErrorMessage        string     `json:"errorMessage"`
+	StartedAt           time.Time  `json:"startedAt"`
+	CompletedAt         *time.Time `json:"completedAt,omitempty"`
+	Locked              bool       `json:"locked"`
+	BackupKind          string     `json:"backupKind"`
 }
 
 type BackupRecordDetail struct {
@@ -184,22 +185,23 @@ func (s *BackupRecordService) SetLock(ctx context.Context, id uint, locked bool)
 
 func toBackupRecordSummary(item *model.BackupRecord) BackupRecordSummary {
 	return BackupRecordSummary{
-		ID:                item.ID,
-		TaskID:            item.TaskID,
-		TaskName:          item.Task.Name,
-		StorageTargetID:   item.StorageTargetID,
-		StorageTargetName: item.StorageTarget.Name,
-		Status:            item.Status,
-		FileName:          item.FileName,
-		FileSize:          item.FileSize,
-		Checksum:          item.Checksum,
-		StoragePath:       item.StoragePath,
-		DurationSeconds:   item.DurationSeconds,
-		ErrorMessage:      item.ErrorMessage,
-		StartedAt:         item.StartedAt,
-		CompletedAt:       item.CompletedAt,
-		Locked:            item.Locked,
-		BackupKind:        item.BackupKind,
+		ID:                  item.ID,
+		TaskID:              item.TaskID,
+		TaskName:            item.Task.Name,
+		StorageTargetID:     item.StorageTargetID,
+		StorageTargetName:   item.StorageTarget.Name,
+		Status:              item.Status,
+		FileName:            item.FileName,
+		FileSize:            item.FileSize,
+		Checksum:            item.Checksum,
+		StoragePath:         item.StoragePath,
+		StorageTransferMode: item.StorageTransferMode,
+		DurationSeconds:     item.DurationSeconds,
+		ErrorMessage:        item.ErrorMessage,
+		StartedAt:           item.StartedAt,
+		CompletedAt:         item.CompletedAt,
+		Locked:              item.Locked,
+		BackupKind:          item.BackupKind,
 	}
 }
 

server/internal/service/execution_helpers.go

@@ -140,6 +140,11 @@ func validateCrossNodeLocalDisk(ctx context.Context, nodeRepo repository.NodeRep
 	if record == nil || record.NodeID == 0 || nodeRepo == nil {
 		return nil
 	}
+	// 中转模式的对象实际落在 Master 配置的本地磁盘，Master 可以安全访问。
+	// 空值和 direct 均按旧版 Agent 本地落盘处理，保持升级兼容。
+	if record.StorageTransferMode == storage.TransferModeMasterRelay {
+		return nil
+	}
 	node, err := nodeRepo.FindByID(ctx, record.NodeID)
 	if err != nil || node == nil || node.IsLocal {
 		return nil

server/internal/service/restore_service.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
 	"strings"
@@ -601,15 +602,22 @@ func (s *RestoreService) GetAgentRestoreSpec(ctx context.Context, node *model.No
 	if target == nil {
 		return nil, apperror.BadRequest("BACKUP_STORAGE_TARGET_INVALID", "存储目标不存在", nil)
 	}
-	configRaw, err := s.cipher.Decrypt(target.ConfigCiphertext)
-	if err != nil {
-		return nil, fmt.Errorf("decrypt storage config: %w", err)
-	}
 	// 拆开 sourcePaths
 	sourcePaths := []string{}
 	if strings.TrimSpace(task.SourcePaths) != "" {
 		_ = json.Unmarshal([]byte(task.SourcePaths), &sourcePaths)
 	}
+	transferMode := storage.TransferModeDirect
+	if backupRecord.StorageTransferMode == storage.TransferModeMasterRelay {
+		transferMode = storage.TransferModeMasterRelay
+	}
+	var configRaw []byte
+	if transferMode == storage.TransferModeDirect {
+		configRaw, err = s.cipher.Decrypt(target.ConfigCiphertext)
+		if err != nil {
+			return nil, fmt.Errorf("decrypt storage config: %w", err)
+		}
+	}
 	return &AgentRestoreSpec{
 		RestoreRecordID: restore.ID,
 		BackupRecordID:  backupRecord.ID,
@@ -628,10 +636,11 @@ func (s *RestoreService) GetAgentRestoreSpec(ctx context.Context, node *model.No
 		Compression:     task.Compression,
 		Encrypt:         task.Encrypt,
 		Storage: AgentStorageTargetConfig{
-			ID:     target.ID,
-			Type:   target.Type,
-			Name:   target.Name,
-			Config: json.RawMessage(configRaw),
+			ID:           target.ID,
+			Type:         target.Type,
+			Name:         target.Name,
+			Config:       json.RawMessage(configRaw),
+			TransferMode: transferMode,
 		},
 		StoragePath: backupRecord.StoragePath,
 		FileName:    backupRecord.FileName,
@@ -639,6 +648,63 @@ func (s *RestoreService) GetAgentRestoreSpec(ctx context.Context, node *model.No
 	}, nil
 }
 
+type AgentArtifactDownload struct {
+	Reader io.ReadCloser
+	Size   int64
+}
+
+// DownloadAgentArtifact opens a Master-local object for authenticated streaming
+// back to the Agent that owns the restore record.
+func (s *RestoreService) DownloadAgentArtifact(ctx context.Context, node *model.Node, restoreID uint) (*AgentArtifactDownload, error) {
+	if node == nil {
+		return nil, apperror.Unauthorized("RESTORE_RECORD_FORBIDDEN", "恢复记录不属于当前节点", nil)
+	}
+	restore, err := s.restores.FindByID(ctx, restoreID)
+	if err != nil {
+		return nil, err
+	}
+	if restore == nil {
+		return nil, apperror.New(404, "RESTORE_RECORD_NOT_FOUND", "恢复记录不存在", nil)
+	}
+	if restore.NodeID != node.ID {
+		return nil, apperror.Unauthorized("RESTORE_RECORD_FORBIDDEN", "恢复记录不属于当前节点", nil)
+	}
+	if isRestoreRecordTerminal(restore.Status) {
+		return nil, apperror.BadRequest("RESTORE_RECORD_TERMINAL", "恢复记录已结束，不能继续下载产物", nil)
+	}
+	record, err := s.records.FindByID(ctx, restore.BackupRecordID)
+	if err != nil {
+		return nil, err
+	}
+	if record == nil {
+		return nil, apperror.New(404, "BACKUP_RECORD_NOT_FOUND", "源备份记录不存在", nil)
+	}
+	target, err := s.targets.FindByID(ctx, record.StorageTargetID)
+	if err != nil {
+		return nil, err
+	}
+	if target == nil || !strings.EqualFold(target.Type, storage.TypeLocalDisk) || record.StorageTransferMode != storage.TransferModeMasterRelay {
+		return nil, apperror.BadRequest("AGENT_ARTIFACT_RELAY_UNSUPPORTED", "该存储目标应由 Agent 直接下载", nil)
+	}
+	configMap := map[string]any{}
+	if err := s.cipher.DecryptJSON(target.ConfigCiphertext, &configMap); err != nil {
+		return nil, fmt.Errorf("decrypt storage config: %w", err)
+	}
+	provider, err := s.storageRegistry.Create(ctx, target.Type, configMap)
+	if err != nil {
+		return nil, fmt.Errorf("create master relay provider: %w", err)
+	}
+	reader, err := provider.Download(ctx, record.StoragePath)
+	if err != nil {
+		return nil, fmt.Errorf("open master relay artifact: %w", err)
+	}
+	size := record.FileSize
+	if size <= 0 {
+		size = -1
+	}
+	return &AgentArtifactDownload{Reader: reader, Size: size}, nil
+}
+
 // UpdateAgentRestore Agent 回传状态/日志。
 func (s *RestoreService) UpdateAgentRestore(ctx context.Context, node *model.Node, restoreID uint, update AgentRestoreUpdate) error {
 	restore, err := s.restores.FindByID(ctx, restoreID)

server/internal/service/restore_service_test.go

@@ -1,8 +1,10 @@
 package service
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
+	"io"
 	"os"
 	"path/filepath"
 	"strings"
@@ -427,16 +429,27 @@ func TestRestoreServiceAgentRestoreAccessUsesRestoreRecordNode(t *testing.T) {
 	}
 	startedAt := time.Now().UTC()
 	completedAt := startedAt.Add(time.Second)
+	artifact := []byte("central backup artifact")
+	storagePath := "file/2026/05/09/remote.tar.gz"
+	artifactPath := filepath.Join(h.storageDir, filepath.FromSlash(storagePath))
+	if err := os.MkdirAll(filepath.Dir(artifactPath), 0o755); err != nil {
+		t.Fatalf("MkdirAll artifact parent: %v", err)
+	}
+	if err := os.WriteFile(artifactPath, artifact, 0o600); err != nil {
+		t.Fatalf("WriteFile artifact: %v", err)
+	}
 	backupRecord := &model.BackupRecord{
-		TaskID:          task.ID,
-		StorageTargetID: task.StorageTargetID,
-		NodeID:          owner.ID,
-		Status:          model.BackupRecordStatusSuccess,
-		FileName:        "remote.tar.gz",
-		StoragePath:     "file/2026/05/09/remote.tar.gz",
-		Checksum:        "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef",
-		StartedAt:       startedAt,
-		CompletedAt:     &completedAt,
+		TaskID:              task.ID,
+		StorageTargetID:     task.StorageTargetID,
+		NodeID:              owner.ID,
+		Status:              model.BackupRecordStatusSuccess,
+		FileName:            "remote.tar.gz",
+		StoragePath:         storagePath,
+		FileSize:            int64(len(artifact)),
+		StorageTransferMode: storage.TransferModeMasterRelay,
+		Checksum:            "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef",
+		StartedAt:           startedAt,
+		CompletedAt:         &completedAt,
 	}
 	if err := h.records.Create(ctx, backupRecord); err != nil {
 		t.Fatalf("Create backup record: %v", err)
@@ -464,6 +477,21 @@ func TestRestoreServiceAgentRestoreAccessUsesRestoreRecordNode(t *testing.T) {
 	if spec.Checksum != backupRecord.Checksum {
 		t.Fatalf("expected spec.Checksum=%q, got %q", backupRecord.Checksum, spec.Checksum)
 	}
+	if spec.Storage.TransferMode != storage.TransferModeMasterRelay {
+		t.Fatalf("expected Master relay restore, got %#v", spec.Storage)
+	}
+	download, err := h.service.DownloadAgentArtifact(ctx, owner, restore.ID)
+	if err != nil {
+		t.Fatalf("DownloadAgentArtifact returned error: %v", err)
+	}
+	downloaded, readErr := io.ReadAll(download.Reader)
+	closeErr := download.Reader.Close()
+	if readErr != nil || closeErr != nil {
+		t.Fatalf("read relayed restore artifact: read=%v close=%v", readErr, closeErr)
+	}
+	if !bytes.Equal(downloaded, artifact) {
+		t.Fatalf("relayed restore artifact differs: %q", downloaded)
+	}
 	if _, err := h.service.GetAgentRestoreSpec(ctx, other, restore.ID); err == nil {
 		t.Fatal("expected non-owner node to be forbidden from restore spec")
 	}

server/internal/storage/types.go

@@ -34,6 +34,14 @@ const (
 	TypeFTP         = string(ProviderTypeFTP)
 )
 
+const (
+	// TransferModeDirect lets an Agent write to a network-accessible backend.
+	TransferModeDirect = "direct"
+	// TransferModeMasterRelay streams an artifact through the authenticated
+	// Agent API so a remote source can use storage mounted only on the Master.
+	TransferModeMasterRelay = "master_relay"
+)
+
 type ObjectInfo struct {
 	Key       string    `json:"key"`
 	Size      int64     `json:"size"`
@@ -99,7 +107,8 @@ func ParseProviderType(value string) ProviderType {
 }
 
 type LocalDiskConfig struct {
-	BasePath string `json:"basePath"`
+	BasePath    string `json:"basePath"`
+	MasterRelay bool   `json:"masterRelay"`
 }
 
 type S3Config struct {