feat(backup): 新增差异备份（differential）模式 (#88)

文件备份新增差异模式：仅打包自上次全量以来的变更并记录删除，恢复自动按全量+差异链还原。含基线解析、链式恢复、保留链保护与本机文件任务校验；清单/比对/删除/往返/保留保护单测全覆盖。

server/internal/backup/file_runner.go

@@ -3,6 +3,7 @@ package backup
 import (
 	"archive/tar"
 	"context"
+	"encoding/json"
 	"fmt"
 	"io"
 	"os"
@@ -52,6 +53,20 @@ func (r *FileRunner) Run(_ context.Context, task TaskSpec, writer LogWriter) (*R
 	defer tw.Close()
 
 	excludes := normalizeExcludePatterns(task.ExcludePatterns)
+
+	// 差异备份：基于上次全量清单仅打包新增/变更条目并记录删除；
+	// 全量备份：记录完整清单（manifest）供后续差异比对。
+	differential := task.Differential && len(task.BaseManifest.Entries) > 0
+	baseIndex := map[string]ManifestEntry{}
+	seen := map[string]struct{}{}
+	var manifest *Manifest
+	if differential {
+		baseIndex = task.BaseManifest.index()
+		writer.WriteLine(fmt.Sprintf("差异备份模式：基线含 %d 个条目", len(baseIndex)))
+	} else {
+		manifest = &Manifest{Entries: make([]ManifestEntry, 0)}
+	}
+
 	totalFileCount := 0
 	totalDirCount := 0
 
@@ -88,6 +103,16 @@ func (r *FileRunner) Run(_ context.Context, task TaskSpec, writer LogWriter) (*R
 				return nil
 			}
 
+			entry := entryFromInfo(archiveName, currentInfo)
+			if differential {
+				seen[entry.Path] = struct{}{}
+				if !changedSince(baseIndex, entry) {
+					return nil // 自全量以来未变更，跳过
+				}
+			} else {
+				manifest.Entries = append(manifest.Entries, entry)
+			}
+
 			if currentInfo.IsDir() {
 				dirCount++
 				writer.WriteLine(fmt.Sprintf("📁 进入目录 %s", archiveName))
@@ -130,10 +155,16 @@ func (r *FileRunner) Run(_ context.Context, task TaskSpec, writer LogWriter) (*R
 		totalDirCount += dirCount
 	}
 
-	if len(sourcePaths) > 1 {
+	if differential {
+		deletions := deletedPaths(baseIndex, seen)
+		if err := writeDeletionsEntry(tw, deletions); err != nil {
+			return nil, err
+		}
+		writer.WriteLine(fmt.Sprintf("差异备份完成（%d 个目录、%d 个文件变更，删除 %d 项）", totalDirCount, totalFileCount, len(deletions)))
+	} else if len(sourcePaths) > 1 {
 		writer.WriteLine(fmt.Sprintf("全部源路径打包完成（共 %d 个目录，%d 个文件）", totalDirCount, totalFileCount))
 	}
-	return &RunResult{ArtifactPath: artifactPath, FileName: filepath.Base(artifactPath), TempDir: tempDir}, nil
+	return &RunResult{ArtifactPath: artifactPath, FileName: filepath.Base(artifactPath), TempDir: tempDir, Manifest: manifest}, nil
 }
 
 func (r *FileRunner) Restore(_ context.Context, task TaskSpec, artifactPath string, writer LogWriter) error {
@@ -151,6 +182,7 @@ func (r *FileRunner) Restore(_ context.Context, task TaskSpec, artifactPath stri
 	if err := os.MkdirAll(targetParent, 0o755); err != nil {
 		return fmt.Errorf("create restore parent: %w", err)
 	}
+	var pendingDeletions []string
 	tr := tar.NewReader(artifactFile)
 	for {
 		header, err := tr.Next()
@@ -160,13 +192,23 @@ func (r *FileRunner) Restore(_ context.Context, task TaskSpec, artifactPath stri
 		if err != nil {
 			return fmt.Errorf("read tar entry: %w", err)
 		}
+		// 差异归档的删除清单不落地，留待提取完成后统一应用（避免被同批新增条目误删）。
+		if header.Name == deletionsEntryName {
+			data, readErr := io.ReadAll(tr)
+			if readErr != nil {
+				return fmt.Errorf("read deletions entry: %w", readErr)
+			}
+			if jsonErr := json.Unmarshal(data, &pendingDeletions); jsonErr != nil {
+				return fmt.Errorf("parse deletions entry: %w", jsonErr)
+			}
+			continue
+		}
 		cleanName := path.Clean(strings.TrimSpace(header.Name))
 		if cleanName == "." || cleanName == "" {
 			continue
 		}
-		targetPath := filepath.Clean(filepath.Join(targetParent, filepath.FromSlash(cleanName)))
-		parentWithSep := filepath.Clean(targetParent) + string(filepath.Separator)
-		if targetPath != filepath.Clean(targetParent) && !strings.HasPrefix(targetPath, parentWithSep) {
+		targetPath, ok := resolveWithinParent(targetParent, cleanName)
+		if !ok {
 			return fmt.Errorf("tar entry escapes restore path")
 		}
 		switch header.Typeflag {
@@ -191,10 +233,65 @@ func (r *FileRunner) Restore(_ context.Context, task TaskSpec, artifactPath stri
 			}
 		}
 	}
+	if err := applyDeletions(targetParent, pendingDeletions, writer); err != nil {
+		return err
+	}
 	writer.WriteLine("文件恢复完成")
 	return nil
 }
 
+// resolveWithinParent 将归档相对名安全解析为 targetParent 下的绝对路径；
+// 越界（路径穿越）时返回 ok=false。提取与删除共用此校验，杜绝逃逸。
+func resolveWithinParent(targetParent, name string) (string, bool) {
+	targetPath := filepath.Clean(filepath.Join(targetParent, filepath.FromSlash(name)))
+	cleanParent := filepath.Clean(targetParent)
+	if targetPath == cleanParent {
+		return targetPath, true
+	}
+	if !strings.HasPrefix(targetPath, cleanParent+string(filepath.Separator)) {
+		return "", false
+	}
+	return targetPath, true
+}
+
+// writeDeletionsEntry 将差异备份的删除路径列表写入归档特殊条目。
+func writeDeletionsEntry(tw *tar.Writer, deletions []string) error {
+	payload, err := json.Marshal(deletions)
+	if err != nil {
+		return fmt.Errorf("marshal deletions: %w", err)
+	}
+	header := &tar.Header{Name: deletionsEntryName, Mode: 0o600, Size: int64(len(payload)), Typeflag: tar.TypeReg}
+	if err := tw.WriteHeader(header); err != nil {
+		return fmt.Errorf("write deletions header: %w", err)
+	}
+	if _, err := tw.Write(payload); err != nil {
+		return fmt.Errorf("write deletions body: %w", err)
+	}
+	return nil
+}
+
+// applyDeletions 在基线恢复之上删除差异归档记录的路径（仅差异备份恢复时存在）。
+// 每个路径经 resolveWithinParent 校验，越界即报错；目标不存在视为已删除。
+func applyDeletions(targetParent string, deletions []string, writer LogWriter) error {
+	for _, name := range deletions {
+		clean := path.Clean(strings.TrimSpace(name))
+		if clean == "." || clean == "" {
+			continue
+		}
+		targetPath, ok := resolveWithinParent(targetParent, clean)
+		if !ok {
+			return fmt.Errorf("deletion entry escapes restore path")
+		}
+		if err := os.RemoveAll(targetPath); err != nil {
+			return fmt.Errorf("apply deletion %s: %w", clean, err)
+		}
+	}
+	if len(deletions) > 0 {
+		writer.WriteLine(fmt.Sprintf("已应用差异删除 %d 项", len(deletions)))
+	}
+	return nil
+}
+
 func normalizeExcludePatterns(items []string) []string {
 	result := make([]string, 0, len(items))
 	for _, item := range items {

server/internal/backup/file_runner_diff_test.go

@@ -0,0 +1,141 @@
+package backup
+
+import (
+	"archive/tar"
+	"context"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func diffWrite(t *testing.T, p, content string) {
+	t.Helper()
+	if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+		t.Fatalf("mkdir %s: %v", filepath.Dir(p), err)
+	}
+	if err := os.WriteFile(p, []byte(content), 0o644); err != nil {
+		t.Fatalf("write %s: %v", p, err)
+	}
+}
+
+func diffAssertContent(t *testing.T, p, want string) {
+	t.Helper()
+	got, err := os.ReadFile(p)
+	if err != nil {
+		t.Fatalf("read %s: %v", p, err)
+	}
+	if string(got) != want {
+		t.Fatalf("%s content = %q, want %q", p, string(got), want)
+	}
+}
+
+func diffAssertAbsent(t *testing.T, p string) {
+	t.Helper()
+	if _, err := os.Stat(p); !os.IsNotExist(err) {
+		t.Fatalf("expected %s to be absent, stat err=%v", p, err)
+	}
+}
+
+func diffArchiveNames(t *testing.T, artifactPath string) map[string]bool {
+	t.Helper()
+	f, err := os.Open(artifactPath)
+	if err != nil {
+		t.Fatalf("open artifact: %v", err)
+	}
+	defer f.Close()
+	names := map[string]bool{}
+	tr := tar.NewReader(f)
+	for {
+		h, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.Fatalf("read tar: %v", err)
+		}
+		names[h.Name] = true
+	}
+	return names
+}
+
+// TestFileRunnerDifferentialRoundTrip 验证差异备份的端到端正确性：
+// 全量 → 修改源（变更/删除/新增）→ 差异 → 链式恢复（全量+差异）→ 结果与修改后源一致。
+func TestFileRunnerDifferentialRoundTrip(t *testing.T) {
+	work := t.TempDir()
+	src := filepath.Join(work, "src")
+	diffWrite(t, filepath.Join(src, "a.txt"), "alpha")
+	diffWrite(t, filepath.Join(src, "b.txt"), "bravo")
+	diffWrite(t, filepath.Join(src, "sub", "c.txt"), "charlie")
+
+	runner := NewFileRunner()
+
+	full, err := runner.Run(context.Background(), TaskSpec{Name: "diff", Type: "file", SourcePath: src, TempDir: t.TempDir()}, NopLogWriter{})
+	if err != nil {
+		t.Fatalf("full Run: %v", err)
+	}
+	if full.Manifest == nil || len(full.Manifest.Entries) == 0 {
+		t.Fatalf("full backup must produce a manifest, got %#v", full.Manifest)
+	}
+
+	// 变更 a.txt（内容变长 → size 差异必被检出）、删除 b.txt、新增 d.txt；sub/c.txt 不变
+	diffWrite(t, filepath.Join(src, "a.txt"), "ALPHA-modified-and-longer")
+	if err := os.Remove(filepath.Join(src, "b.txt")); err != nil {
+		t.Fatalf("remove b.txt: %v", err)
+	}
+	diffWrite(t, filepath.Join(src, "d.txt"), "delta")
+
+	diff, err := runner.Run(context.Background(), TaskSpec{Name: "diff", Type: "file", SourcePath: src, TempDir: t.TempDir(), Differential: true, BaseManifest: *full.Manifest}, NopLogWriter{})
+	if err != nil {
+		t.Fatalf("differential Run: %v", err)
+	}
+	if diff.Manifest != nil {
+		t.Fatalf("differential backup must not produce a manifest")
+	}
+
+	// 差异归档应包含变更/新增条目与删除清单，但不含未变更的 sub/c.txt
+	names := diffArchiveNames(t, diff.ArtifactPath)
+	if !names["src/a.txt"] || !names["src/d.txt"] {
+		t.Fatalf("differential archive missing changed/new entries: %v", names)
+	}
+	if names["src/sub/c.txt"] {
+		t.Fatalf("differential archive should not contain unchanged file sub/c.txt")
+	}
+	if !names[deletionsEntryName] {
+		t.Fatalf("differential archive missing deletions entry: %v", names)
+	}
+
+	// 链式恢复到全新目标
+	restoreRoot := t.TempDir()
+	restoreSrc := filepath.Join(restoreRoot, "src")
+	restoreTask := TaskSpec{Name: "diff", Type: "file", SourcePath: restoreSrc}
+	if err := runner.Restore(context.Background(), restoreTask, full.ArtifactPath, NopLogWriter{}); err != nil {
+		t.Fatalf("restore full: %v", err)
+	}
+	if err := runner.Restore(context.Background(), restoreTask, diff.ArtifactPath, NopLogWriter{}); err != nil {
+		t.Fatalf("restore differential: %v", err)
+	}
+
+	diffAssertContent(t, filepath.Join(restoreSrc, "a.txt"), "ALPHA-modified-and-longer")
+	diffAssertContent(t, filepath.Join(restoreSrc, "sub", "c.txt"), "charlie")
+	diffAssertContent(t, filepath.Join(restoreSrc, "d.txt"), "delta")
+	diffAssertAbsent(t, filepath.Join(restoreSrc, "b.txt"))
+}
+
+// TestFileRunnerDifferentialWithoutBaseIsFull 验证无基线时差异请求回退为全量（产出清单、含全部文件）。
+func TestFileRunnerDifferentialWithoutBaseIsFull(t *testing.T) {
+	src := filepath.Join(t.TempDir(), "src")
+	diffWrite(t, filepath.Join(src, "a.txt"), "alpha")
+
+	runner := NewFileRunner()
+	res, err := runner.Run(context.Background(), TaskSpec{Name: "diff", Type: "file", SourcePath: src, TempDir: t.TempDir(), Differential: true}, NopLogWriter{})
+	if err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+	if res.Manifest == nil {
+		t.Fatalf("differential without base must fall back to full and produce a manifest")
+	}
+	if names := diffArchiveNames(t, res.ArtifactPath); !names["src/a.txt"] || names[deletionsEntryName] {
+		t.Fatalf("fallback-full archive unexpected: %v", names)
+	}
+}

server/internal/backup/manifest.go

@@ -0,0 +1,92 @@
+package backup
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"sort"
+)
+
+// deletionsEntryName 是差异备份归档中记录「自全量以来被删除路径」的特殊条目名。
+// 恢复时该条目不落地为文件，而是用于在基线之上删除对应路径。
+const deletionsEntryName = ".backupx/deletions.json"
+
+// ManifestEntry 记录一次全量备份中单个归档条目（文件或目录）的指纹，
+// 供差异备份比对「自全量以来的变化」。Path 为归档内相对名（slash 分隔，
+// 与 tar header.Name 一致）。字段使用短键以压缩清单体积。
+type ManifestEntry struct {
+	Path      string `json:"p"`
+	Size      int64  `json:"s"`
+	ModTimeNs int64  `json:"m"`
+	Mode      uint32 `json:"o"`
+	IsDir     bool   `json:"d,omitempty"`
+}
+
+// Manifest 是一次全量备份的完整条目清单（文件与目录）。
+type Manifest struct {
+	Entries []ManifestEntry `json:"entries"`
+}
+
+// EncodeManifest 将清单序列化为紧凑 JSON。
+func EncodeManifest(m Manifest) ([]byte, error) {
+	return json.Marshal(m)
+}
+
+// DecodeManifest 反序列化清单；空输入返回空清单（视为「无基线」）。
+func DecodeManifest(data []byte) (Manifest, error) {
+	m := Manifest{}
+	if len(data) == 0 {
+		return m, nil
+	}
+	if err := json.Unmarshal(data, &m); err != nil {
+		return Manifest{}, err
+	}
+	return m, nil
+}
+
+// index 构建 path -> entry 映射，便于差异比对 O(1) 查找。
+func (m Manifest) index() map[string]ManifestEntry {
+	idx := make(map[string]ManifestEntry, len(m.Entries))
+	for _, e := range m.Entries {
+		idx[e.Path] = e
+	}
+	return idx
+}
+
+// entryFromInfo 由归档名与文件信息构造指纹条目。
+func entryFromInfo(archiveName string, info os.FileInfo) ManifestEntry {
+	return ManifestEntry{
+		Path:      filepath.ToSlash(archiveName),
+		Size:      info.Size(),
+		ModTimeNs: info.ModTime().UnixNano(),
+		Mode:      uint32(info.Mode().Perm()),
+		IsDir:     info.IsDir(),
+	}
+}
+
+// changedSince 判断当前条目相对基线是否为「新增或变更」（即应纳入差异归档）。
+//   - 不在基线中 → 新增，纳入；
+//   - 已存在的目录 → 不携带数据，跳过（其下变更文件会各自判定）；
+//   - 文件大小或 mtime 变化 → 变更，纳入（rsync 风格启发式）。
+func changedSince(base map[string]ManifestEntry, cur ManifestEntry) bool {
+	prev, ok := base[cur.Path]
+	if !ok {
+		return true
+	}
+	if cur.IsDir {
+		return false
+	}
+	return prev.Size != cur.Size || prev.ModTimeNs != cur.ModTimeNs
+}
+
+// deletedPaths 返回基线中存在、但本次遍历未出现的路径（被删除的条目），按路径升序。
+func deletedPaths(base map[string]ManifestEntry, seen map[string]struct{}) []string {
+	deleted := make([]string, 0)
+	for p := range base {
+		if _, ok := seen[p]; !ok {
+			deleted = append(deleted, p)
+		}
+	}
+	sort.Strings(deleted)
+	return deleted
+}

server/internal/backup/manifest_test.go

@@ -0,0 +1,79 @@
+package backup
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestEncodeDecodeManifestRoundTrip(t *testing.T) {
+	m := Manifest{Entries: []ManifestEntry{
+		{Path: "src/a.txt", Size: 10, ModTimeNs: 100, Mode: 0o644},
+		{Path: "src", Size: 0, ModTimeNs: 50, Mode: 0o755, IsDir: true},
+	}}
+	data, err := EncodeManifest(m)
+	if err != nil {
+		t.Fatalf("EncodeManifest: %v", err)
+	}
+	got, err := DecodeManifest(data)
+	if err != nil {
+		t.Fatalf("DecodeManifest: %v", err)
+	}
+	if !reflect.DeepEqual(got, m) {
+		t.Fatalf("roundtrip mismatch:\n got %#v\nwant %#v", got, m)
+	}
+}
+
+func TestDecodeManifestEmpty(t *testing.T) {
+	got, err := DecodeManifest(nil)
+	if err != nil {
+		t.Fatalf("DecodeManifest(nil): %v", err)
+	}
+	if len(got.Entries) != 0 {
+		t.Fatalf("expected empty manifest, got %#v", got)
+	}
+}
+
+func TestChangedSince(t *testing.T) {
+	base := Manifest{Entries: []ManifestEntry{
+		{Path: "a.txt", Size: 10, ModTimeNs: 100},
+		{Path: "dir", IsDir: true, ModTimeNs: 100},
+	}}.index()
+
+	cases := []struct {
+		name string
+		cur  ManifestEntry
+		want bool
+	}{
+		{"unchanged file", ManifestEntry{Path: "a.txt", Size: 10, ModTimeNs: 100}, false},
+		{"size changed", ManifestEntry{Path: "a.txt", Size: 11, ModTimeNs: 100}, true},
+		{"mtime changed", ManifestEntry{Path: "a.txt", Size: 10, ModTimeNs: 200}, true},
+		{"new file", ManifestEntry{Path: "b.txt", Size: 1, ModTimeNs: 1}, true},
+		{"existing dir skipped", ManifestEntry{Path: "dir", IsDir: true, ModTimeNs: 999}, false},
+		{"new dir included", ManifestEntry{Path: "newdir", IsDir: true, ModTimeNs: 1}, true},
+	}
+	for _, tc := range cases {
+		if got := changedSince(base, tc.cur); got != tc.want {
+			t.Errorf("%s: changedSince=%v want %v", tc.name, got, tc.want)
+		}
+	}
+}
+
+func TestDeletedPaths(t *testing.T) {
+	base := Manifest{Entries: []ManifestEntry{
+		{Path: "a"}, {Path: "b"}, {Path: "c"},
+	}}.index()
+	seen := map[string]struct{}{"a": {}, "c": {}}
+	got := deletedPaths(base, seen)
+	want := []string{"b"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("deletedPaths=%v want %v", got, want)
+	}
+}
+
+func TestDeletedPathsNoneWhenAllSeen(t *testing.T) {
+	base := Manifest{Entries: []ManifestEntry{{Path: "a"}, {Path: "b"}}}.index()
+	seen := map[string]struct{}{"a": {}, "b": {}}
+	if got := deletedPaths(base, seen); len(got) != 0 {
+		t.Fatalf("expected no deletions, got %v", got)
+	}
+}

server/internal/backup/retention/differential_test.go

@@ -0,0 +1,55 @@
+package retention
+
+import (
+	"testing"
+
+	"backupx/server/internal/model"
+)
+
+func retentionRecIDs(records []model.BackupRecord) []uint {
+	ids := make([]uint, 0, len(records))
+	for _, r := range records {
+		ids = append(ids, r.ID)
+	}
+	return ids
+}
+
+// 基线全量仍被「不在删除集合中的差异」依赖 → 必须保留，否则差异无法恢复。
+func TestProtectDifferentialBasesKeepsBaseWithSurvivingDiff(t *testing.T) {
+	all := []model.BackupRecord{
+		{ID: 1, BackupKind: model.BackupKindFull},
+		{ID: 2, BackupKind: model.BackupKindDifferential, BaseRecordID: 1},
+	}
+	candidates := []model.BackupRecord{{ID: 1, BackupKind: model.BackupKindFull}}
+	if got := protectDifferentialBases(all, candidates); len(got) != 0 {
+		t.Fatalf("base with surviving diff must be protected, got %v", retentionRecIDs(got))
+	}
+}
+
+// 基线全量与其全部差异都在删除集合中 → 可一并删除（无残留差异失去基线）。
+func TestProtectDifferentialBasesDeletesBaseWhenDiffAlsoDeleted(t *testing.T) {
+	all := []model.BackupRecord{
+		{ID: 1, BackupKind: model.BackupKindFull},
+		{ID: 2, BackupKind: model.BackupKindDifferential, BaseRecordID: 1},
+	}
+	candidates := []model.BackupRecord{
+		{ID: 1, BackupKind: model.BackupKindFull},
+		{ID: 2, BackupKind: model.BackupKindDifferential, BaseRecordID: 1},
+	}
+	if got := protectDifferentialBases(all, candidates); len(got) != 2 {
+		t.Fatalf("base+diff both expired should both be deleted, got %v", retentionRecIDs(got))
+	}
+}
+
+// 无差异备份时原样透传（不影响既有全量保留逻辑）。
+func TestProtectDifferentialBasesNoDiffsPassThrough(t *testing.T) {
+	all := []model.BackupRecord{
+		{ID: 1, BackupKind: model.BackupKindFull},
+		{ID: 2, BackupKind: model.BackupKindFull},
+	}
+	candidates := []model.BackupRecord{{ID: 1, BackupKind: model.BackupKindFull}}
+	got := protectDifferentialBases(all, candidates)
+	if len(got) != 1 || got[0].ID != 1 {
+		t.Fatalf("no diffs should pass through unchanged, got %v", retentionRecIDs(got))
+	}
+}

server/internal/backup/retention/service.go

@@ -64,6 +64,8 @@ func (s *Service) Cleanup(ctx context.Context, task *model.BackupTask, provider
 	} else {
 		candidates = selectRecordsToDelete(records, task.RetentionDays, task.MaxBackups, s.now())
 	}
+	// 差异链保护：保留仍被存活差异依赖的全量，避免删除基线后差异无法恢复。
+	candidates = protectDifferentialBases(records, candidates)
 	result := &CleanupResult{}
 	for _, record := range candidates {
 		if strings.TrimSpace(record.StoragePath) != "" {
@@ -97,6 +99,38 @@ func (s *Service) Cleanup(ctx context.Context, task *model.BackupTask, provider
 	return result, nil
 }
 
+// protectDifferentialBases 从删除候选中剔除「仍被存活差异依赖的全量」，
+// 避免删除基线后其差异备份失去依据、无法恢复。全量仅当其全部差异都已过期/删除时才会被清理。
+func protectDifferentialBases(all []model.BackupRecord, candidates []model.BackupRecord) []model.BackupRecord {
+	deleting := make(map[uint]struct{}, len(candidates))
+	for _, r := range candidates {
+		deleting[r.ID] = struct{}{}
+	}
+	protected := make(map[uint]struct{})
+	for _, r := range all {
+		if r.BackupKind != model.BackupKindDifferential || r.BaseRecordID == 0 {
+			continue
+		}
+		if _, beingDeleted := deleting[r.ID]; beingDeleted {
+			continue // 该差异本身也将被删除，无需保护其基线
+		}
+		protected[r.BaseRecordID] = struct{}{}
+	}
+	if len(protected) == 0 {
+		return candidates
+	}
+	filtered := make([]model.BackupRecord, 0, len(candidates))
+	for _, r := range candidates {
+		if r.BackupKind == model.BackupKindFull {
+			if _, keep := protected[r.ID]; keep {
+				continue
+			}
+		}
+		filtered = append(filtered, r)
+	}
+	return filtered
+}
+
 func selectRecordsToDelete(records []model.BackupRecord, retentionDays int, maxBackups int, now time.Time) []model.BackupRecord {
 	// 保留锁定（法律保留）的记录永不参与清理：先从候选集中剔除，
 	// 锁定备份既不被删除，也不占用 maxBackups 轮转名额。

server/internal/backup/types.go

@@ -36,6 +36,10 @@ type TaskSpec struct {
 	MaxBackups        int
 	StartedAt         time.Time
 	TempDir           string
+	// Differential 为 true 时执行差异备份：仅打包自 BaseManifest 以来新增/变更的条目，
+	// 并记录被删除的路径。仅文件类型任务支持；BaseManifest 为空时回退为全量。
+	Differential bool
+	BaseManifest Manifest
 }
 
 type RunResult struct {
@@ -44,6 +48,8 @@ type RunResult struct {
 	TempDir      string
 	Size         int64
 	StorageKey   string
+	// Manifest 为全量备份产出的条目清单，供后续差异备份比对；差异备份运行时为 nil。
+	Manifest *Manifest
 }
 
 type LogEvent struct {
@@ -62,7 +68,7 @@ type ProgressInfo struct {
 	BytesSent  int64   `json:"bytesSent"`
 	TotalBytes int64   `json:"totalBytes"`
 	Percent    float64 `json:"percent"`
-	SpeedBps   float64 `json:"speedBps"`   // bytes/sec
+	SpeedBps   float64 `json:"speedBps"` // bytes/sec
 	TargetName string  `json:"targetName"`
 }