diff --git a/backend/internal/logic/ai/handlers_test.go b/backend/internal/logic/ai/handlers_test.go
index 6c32e8e..58cd258 100644
--- a/backend/internal/logic/ai/handlers_test.go
+++ b/backend/internal/logic/ai/handlers_test.go
@@ -159,7 +159,7 @@ func TestCreateAISessionWithoutKeyReturnsAuditedErrorAndCreatesNoFormalObjects(t
 	for _, model := range []any{
 		&models.SaAISession{},
 		&models.SaTask{},
-		&models.SaDocument{},
+		&models.SaDocumentTree{},
 	} {
 		var count int64
 		require.NoError(t, database.Model(model).Count(&count).Error)
@@ -272,7 +272,7 @@ func TestCreateAISessionReturnsIdentityDTOAndCompleteAuditWithoutAutomaticObject
 	require.Equal(t, "ai_session_create", call.Action)
 	require.Equal(t, "ready", call.Status)
 	require.Empty(t, call.Error)
-	for _, model := range []any{&models.SaTask{}, &models.SaDocument{}} {
+	for _, model := range []any{&models.SaTask{}, &models.SaDocumentTree{}} {
 		var count int64
 		require.NoError(t, database.Model(model).Count(&count).Error)
 		require.Zero(t, count)
diff --git a/backend/internal/logic/dataset/handlers_test.go b/backend/internal/logic/dataset/handlers_test.go
index 71f4fef..fd47575 100644
--- a/backend/internal/logic/dataset/handlers_test.go
+++ b/backend/internal/logic/dataset/handlers_test.go
@@ -90,7 +90,7 @@ func TestDatasetAPIConnectsSourcesItemsAndSyncTasks(t *testing.T) {
 		"projectId": project.Identity,
 	})
 	require.Equal(t, http.StatusCreated, deposited.Code)
-	var depositedDocument models.SaDocument
+	var depositedDocument models.SaDocumentTree
 	require.NoError(t, database.Where("project_id = ?", project.ID).First(&depositedDocument).Error)
 	require.Equal(t, item.Title+".md", depositedDocument.Name)
 	var depositedContent models.SaDocumentContent
@@ -241,7 +241,7 @@ func newDatasetTestDatabase(t *testing.T) *gorm.DB {
 		&models.SaDatasetSource{},
 		&models.SaDatasetItem{},
 		&models.SaProject{},
-		&models.SaDocument{},
+		&models.SaDocumentTree{},
 		&models.SaDocumentContent{},
 	))
 	return database
diff --git a/backend/internal/logic/dataset/service.go b/backend/internal/logic/dataset/service.go
index 5cc864f..65ab8c7 100644
--- a/backend/internal/logic/dataset/service.go
+++ b/backend/internal/logic/dataset/service.go
@@ -75,7 +75,7 @@ type ItemPatch struct {
 
 type DepositResult struct {
 	DocumentIdentity string
-	ProjectIdentity string
+	ProjectIdentity  string
 }
 
 type SourceRecord struct {
@@ -363,9 +363,9 @@ func (s *Service) DepositItem(userID uint, itemIdentity, projectIdentity string)
 	if !strings.HasSuffix(strings.ToLower(name), ".md") {
 		name += ".md"
 	}
-	var document models.SaDocument
+	var document models.SaDocumentTree
 	err = s.db.Transaction(func(tx *gorm.DB) error {
-		document = models.SaDocument{
+		document = models.SaDocumentTree{
 			ProjectID: project.ID, CreatedBy: userID, Kind: models.DocumentKindFile,
 			Name: name, NormalizedName: strings.ToLower(name), Extension: ".md",
 			MimeType: "text/markdown; charset=utf-8", Size: int64(len([]byte(body))),
diff --git a/backend/internal/logic/documents/handlers.go b/backend/internal/logic/documents/handlers.go
index 9b09e42..63e7ad8 100644
--- a/backend/internal/logic/documents/handlers.go
+++ b/backend/internal/logic/documents/handlers.go
@@ -145,7 +145,7 @@ func (h *Handler) create(c *gin.Context, folder bool) {
 		}
 		input.SourceInboxItemID = &inbox.ID
 	}
-	var document *models.SaDocument
+	var document *models.SaDocumentTree
 	var err error
 	if folder {
 		document, err = h.service.CreateFolder(userID, projectID, input)
@@ -496,7 +496,7 @@ func requestScope(c *gin.Context) (uint, string, bool) {
 	return userID, projectID, ok
 }
 
-func documentDTO(document models.SaDocument, markdown *string, hasBlob bool) DocumentDTO {
+func documentDTO(document models.SaDocumentTree, markdown *string, hasBlob bool) DocumentDTO {
 	return DocumentDTO{
 		ID: document.Identity, ProjectID: document.ProjectIdentity, ParentID: document.ParentIdentity,
 		Kind: document.Kind, Name: document.Name, Extension: document.Extension, MimeType: document.MimeType,
diff --git a/backend/internal/logic/documents/handlers_test.go b/backend/internal/logic/documents/handlers_test.go
index ec747cd..9b14c82 100644
--- a/backend/internal/logic/documents/handlers_test.go
+++ b/backend/internal/logic/documents/handlers_test.go
@@ -10,7 +10,7 @@ import (
 
 func TestSharedPreviewBodySanitizesMarkdownHTMLAndUnsafeLinks(t *testing.T) {
 	body := sharedPreviewBody(SharedDocument{
-		Document: models.SaDocument{Name: "shared.md", Extension: ".md"},
+		Document: models.SaDocumentTree{Name: "shared.md", Extension: ".md"},
 		Content: &models.SaDocumentContent{
 			Markdown: "# 标题\n\n<script>alert(1)</script>\n\n[危险链接](javascript:alert(2))",
 		},
@@ -23,7 +23,7 @@ func TestSharedPreviewBodySanitizesMarkdownHTMLAndUnsafeLinks(t *testing.T) {
 
 func TestSharedPreviewBodyEmbedsSupportedBlobWithoutDownloadLink(t *testing.T) {
 	body := sharedPreviewBody(SharedDocument{
-		Document: models.SaDocument{Name: "manual.pdf", Extension: ".pdf", MimeType: "application/pdf"},
+		Document: models.SaDocumentTree{Name: "manual.pdf", Extension: ".pdf", MimeType: "application/pdf"},
 		Blob:     &models.SaDocumentBlob{StorageKey: "blob"},
 	}, "https://example.test/content")
 
diff --git a/backend/internal/logic/documents/service.go b/backend/internal/logic/documents/service.go
index 50bc7c6..0a6e67d 100644
--- a/backend/internal/logic/documents/service.go
+++ b/backend/internal/logic/documents/service.go
@@ -69,7 +69,7 @@ type StoredBlob struct {
 }
 
 type SharedDocument struct {
-	Document models.SaDocument
+	Document models.SaDocumentTree
 	Content  *models.SaDocumentContent
 	Blob     *models.SaDocumentBlob
 }
@@ -94,26 +94,26 @@ func (s *Service) database() *gorm.DB {
 	return models.DBService
 }
 
-func (s *Service) List(userID uint, projectIdentity string) ([]models.SaDocument, error) {
+func (s *Service) List(userID uint, projectIdentity string) ([]models.SaDocumentTree, error) {
 	project, err := s.ownedProject(userID, projectIdentity)
 	if err != nil {
 		return nil, err
 	}
-	var documents []models.SaDocument
+	var documents []models.SaDocumentTree
 	err = s.database().Where("project_id = ?", project.ID).
 		Order("kind asc, normalized_name asc, id asc").Find(&documents).Error
 	return documents, err
 }
 
-func (s *Service) CreateFolder(userID uint, projectIdentity string, input CreateInput) (*models.SaDocument, error) {
+func (s *Service) CreateFolder(userID uint, projectIdentity string, input CreateInput) (*models.SaDocumentTree, error) {
 	return s.createNode(userID, projectIdentity, input, models.DocumentKindFolder, "", "", 0)
 }
 
-func (s *Service) CreateMarkdown(userID uint, projectIdentity string, input CreateInput) (*models.SaDocument, error) {
+func (s *Service) CreateMarkdown(userID uint, projectIdentity string, input CreateInput) (*models.SaDocumentTree, error) {
 	if strings.TrimSpace(filepath.Ext(input.Name)) == "" {
 		input.Name += ".md"
 	}
-	var created *models.SaDocument
+	var created *models.SaDocumentTree
 	err := s.database().Transaction(func(tx *gorm.DB) error {
 		service := NewService(tx, s.root)
 		document, err := service.createNode(userID, projectIdentity, input, models.DocumentKindFile, ".md", "text/markdown; charset=utf-8", int64(len([]byte(input.Markdown))))
@@ -129,7 +129,7 @@ func (s *Service) CreateMarkdown(userID uint, projectIdentity string, input Crea
 	return created, err
 }
 
-func (s *Service) createNode(userID uint, projectIdentity string, input CreateInput, kind, extension, mimeType string, size int64) (*models.SaDocument, error) {
+func (s *Service) createNode(userID uint, projectIdentity string, input CreateInput, kind, extension, mimeType string, size int64) (*models.SaDocumentTree, error) {
 	project, err := s.ownedProject(userID, projectIdentity)
 	if err != nil {
 		return nil, err
@@ -149,11 +149,11 @@ func (s *Service) createNode(userID uint, projectIdentity string, input CreateIn
 	if kind == models.DocumentKindFile {
 		extension = strings.ToLower(filepath.Ext(name))
 	}
-	document := &models.SaDocument{
+	document := &models.SaDocumentTree{
 		ProjectID: project.ID, ProjectIdentity: project.Identity,
 		ParentID: parentID, ParentIdentity: parentIdentity,
 		ParentScope: identityValue(parentIdentity),
-		CreatedBy: userID, SourceInboxItemID: input.SourceInboxItemID,
+		CreatedBy:   userID, SourceInboxItemID: input.SourceInboxItemID,
 		Kind: kind, Name: name, NormalizedName: normalizeName(name),
 		Extension: extension, MimeType: mimeType, Size: size, Revision: 1,
 		ScanStatus: "not_scanned",
@@ -167,8 +167,8 @@ func (s *Service) createNode(userID uint, projectIdentity string, input CreateIn
 	return document, nil
 }
 
-func (s *Service) CreateUploaded(userID uint, projectIdentity, parentIdentity string, stored StoredBlob) (*models.SaDocument, error) {
-	var created *models.SaDocument
+func (s *Service) CreateUploaded(userID uint, projectIdentity, parentIdentity string, stored StoredBlob) (*models.SaDocumentTree, error) {
+	var created *models.SaDocumentTree
 	err := s.database().Transaction(func(tx *gorm.DB) error {
 		service := NewService(tx, s.root)
 		document, err := service.createNode(userID, projectIdentity, CreateInput{
@@ -197,7 +197,7 @@ func (s *Service) Get(userID uint, projectIdentity, documentIdentity string) (*S
 	if err != nil {
 		return nil, err
 	}
-	var document models.SaDocument
+	var document models.SaDocumentTree
 	if err := s.database().Where("identity = ? AND project_id = ?", strings.TrimSpace(documentIdentity), project.ID).First(&document).Error; err != nil {
 		return nil, err
 	}
@@ -212,7 +212,7 @@ func (s *Service) Update(userID uint, projectIdentity, documentIdentity string,
 		if err != nil {
 			return err
 		}
-		var document models.SaDocument
+		var document models.SaDocumentTree
 		if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).
 			Where("identity = ? AND project_id = ?", strings.TrimSpace(documentIdentity), project.ID).
 			First(&document).Error; err != nil {
@@ -306,7 +306,7 @@ func (s *Service) Delete(userID uint, projectIdentity, documentIdentity string)
 	if err != nil {
 		return err
 	}
-	var document models.SaDocument
+	var document models.SaDocumentTree
 	if err := s.database().Where("identity = ? AND project_id = ?", documentIdentity, project.ID).First(&document).Error; err != nil {
 		return err
 	}
@@ -314,7 +314,7 @@ func (s *Service) Delete(userID uint, projectIdentity, documentIdentity string)
 	if err != nil {
 		return err
 	}
-	return s.database().Where("id IN ?", ids).Delete(&models.SaDocument{}).Error
+	return s.database().Where("id IN ?", ids).Delete(&models.SaDocumentTree{}).Error
 }
 
 func (s *Service) Store(projectIdentity, originalName string, source io.Reader) (StoredBlob, error) {
@@ -482,7 +482,7 @@ func (s *Service) ResolveShare(token string) (*SharedDocument, error) {
 	).First(&share).Error; err != nil {
 		return nil, ErrShareNotFound
 	}
-	var document models.SaDocument
+	var document models.SaDocumentTree
 	if err := s.database().Where("id = ?", share.DocumentID).First(&document).Error; err != nil {
 		return nil, ErrShareNotFound
 	}
@@ -508,7 +508,7 @@ func (s *Service) Export(document SharedDocument, format string) ([]byte, string
 	}
 }
 
-func (s *Service) loadDocument(document models.SaDocument) (*SharedDocument, error) {
+func (s *Service) loadDocument(document models.SaDocumentTree) (*SharedDocument, error) {
 	result := &SharedDocument{Document: document}
 	var content models.SaDocumentContent
 	if err := s.database().Where("document_id = ?", document.ID).First(&content).Error; err == nil {
@@ -536,7 +536,7 @@ func (s *Service) resolveParent(projectID uint, identity string) (*uint, *string
 	if identity == "" {
 		return nil, nil, nil
 	}
-	var parent models.SaDocument
+	var parent models.SaDocumentTree
 	if err := s.database().Where("identity = ? AND project_id = ? AND kind = ?", identity, projectID, models.DocumentKindFolder).First(&parent).Error; err != nil {
 		return nil, nil, ErrInvalidParent
 	}
@@ -559,7 +559,7 @@ func (s *Service) availableName(projectID uint, parentID *uint, name string) (st
 }
 
 func (s *Service) nameExists(projectID uint, parentID *uint, normalized string, exceptID uint) bool {
-	query := s.database().Model(&models.SaDocument{}).Where("project_id = ? AND normalized_name = ?", projectID, normalized)
+	query := s.database().Model(&models.SaDocumentTree{}).Where("project_id = ? AND normalized_name = ?", projectID, normalized)
 	if parentID == nil {
 		query = query.Where("parent_id IS NULL")
 	} else {
@@ -578,7 +578,7 @@ func (s *Service) isDescendant(ancestorID, candidateID uint) (bool, error) {
 		if current == ancestorID {
 			return true, nil
 		}
-		var document models.SaDocument
+		var document models.SaDocumentTree
 		if err := s.database().Unscoped().Select("parent_id").Where("id = ?", current).First(&document).Error; err != nil {
 			return false, err
 		}
@@ -594,7 +594,7 @@ func (s *Service) subtreeIDs(projectID, rootID uint) ([]uint, error) {
 	result := []uint{rootID}
 	frontier := []uint{rootID}
 	for len(frontier) > 0 {
-		var children []models.SaDocument
+		var children []models.SaDocumentTree
 		if err := s.database().Select("id").Where("project_id = ? AND parent_id IN ?", projectID, frontier).Find(&children).Error; err != nil {
 			return nil, err
 		}
diff --git a/backend/internal/logic/documents/service_test.go b/backend/internal/logic/documents/service_test.go
index 70115d1..92ce806 100644
--- a/backend/internal/logic/documents/service_test.go
+++ b/backend/internal/logic/documents/service_test.go
@@ -60,10 +60,10 @@ func TestDocumentTreeRevisionMoveDeleteAndShareLifecycle(t *testing.T) {
 
 	require.NoError(t, service.Delete(user.ID, project.Identity, folder.Identity))
 	var visible int64
-	require.NoError(t, database.Model(&models.SaDocument{}).Where("project_id = ?", project.ID).Count(&visible).Error)
+	require.NoError(t, database.Model(&models.SaDocumentTree{}).Where("project_id = ?", project.ID).Count(&visible).Error)
 	require.Zero(t, visible)
 	var retained int64
-	require.NoError(t, database.Unscoped().Model(&models.SaDocument{}).Where("project_id = ?", project.ID).Count(&retained).Error)
+	require.NoError(t, database.Unscoped().Model(&models.SaDocumentTree{}).Where("project_id = ?", project.ID).Count(&retained).Error)
 	require.Equal(t, int64(3), retained)
 }
 
diff --git a/backend/internal/logic/inbox/service.go b/backend/internal/logic/inbox/service.go
index 6c1688d..a8540ab 100644
--- a/backend/internal/logic/inbox/service.go
+++ b/backend/internal/logic/inbox/service.go
@@ -279,7 +279,7 @@ func createConfirmedObject(tx *gorm.DB, item models.SaInboxItem, suggestion mode
 		if !strings.HasSuffix(strings.ToLower(name), ".md") {
 			name += ".md"
 		}
-		document := models.SaDocument{
+		document := models.SaDocumentTree{
 			ProjectID: item.ProjectID, ProjectIdentity: item.ProjectIdentity, CreatedBy: item.CreatedBy,
 			SourceInboxItemID: &sourceInboxItemID, Kind: models.DocumentKindFile, Name: name,
 			NormalizedName: strings.ToLower(name), Extension: ".md", MimeType: "text/markdown; charset=utf-8",
diff --git a/backend/internal/logic/inbox/service_test.go b/backend/internal/logic/inbox/service_test.go
index 22e6de6..4e08e69 100644
--- a/backend/internal/logic/inbox/service_test.go
+++ b/backend/internal/logic/inbox/service_test.go
@@ -155,7 +155,7 @@ func TestConfirmCreatesOnlySelectedSavedSuggestionsWithInboxIdentity(t *testing.
 	require.Equal(t, fixture.owner.ID, task.CreatedBy)
 	requireSourceInboxIdentity(t, item, task.SourceInboxItemID, task.SourceInboxItemIdentity)
 
-	var documents []models.SaDocument
+	var documents []models.SaDocumentTree
 	require.NoError(t, fixture.database.Order("id asc").Find(&documents).Error)
 	require.Len(t, documents, 2)
 	require.Equal(t, "会议纪要.md", documents[0].Name)
@@ -231,7 +231,7 @@ func TestConfirmIsTransactionalWhenASelectedWriteFails(t *testing.T) {
 
 	const callbackName = "test:fail_inbox_document_create"
 	require.NoError(t, fixture.database.Callback().Create().Before("gorm:create").Register(callbackName, func(tx *gorm.DB) {
-		document, ok := tx.Statement.Dest.(*models.SaDocument)
+		document, ok := tx.Statement.Dest.(*models.SaDocumentTree)
 		if ok && document.Name == "失败资料.md" {
 			tx.AddError(errors.New("simulated source write failure"))
 		}
@@ -266,7 +266,7 @@ func TestRepeatedConfirmReturnsPersistedResultAfterRelatedObjectsChange(t *testi
 	requireFormalObjectCounts(t, fixture.database, 1, 1, 0)
 
 	sourceInboxItemID := item.ID
-	extraDocument := models.SaDocument{
+	extraDocument := models.SaDocumentTree{
 		ProjectID: item.ProjectID, CreatedBy: fixture.owner.ID, SourceInboxItemID: &sourceInboxItemID,
 		Kind: models.DocumentKindFile, Name: "后续关联资料.md", NormalizedName: "后续关联资料.md",
 		Extension: ".md", Revision: 1,
@@ -348,7 +348,7 @@ func requireFormalObjectCounts(t *testing.T, database *gorm.DB, tasks, notes, so
 		want  int64
 	}{
 		{model: &models.SaTask{}, want: tasks},
-		{model: &models.SaDocument{}, want: notes + sources},
+		{model: &models.SaDocumentTree{}, want: notes + sources},
 	} {
 		var count int64
 		require.NoError(t, database.Model(check.model).Count(&count).Error)
diff --git a/backend/internal/logic/projects/service_test.go b/backend/internal/logic/projects/service_test.go
index 9d94a4f..2b55a43 100644
--- a/backend/internal/logic/projects/service_test.go
+++ b/backend/internal/logic/projects/service_test.go
@@ -127,8 +127,8 @@ func TestWorkspaceMatchesFrontendContract(t *testing.T) {
 	require.NoError(t, database.Create(&models.SaTask{ProjectID: project.ID, CreatedBy: 1, Title: "Confirm IA", Description: "Review channel layout.", Status: "open", DueAt: &nextRun}).Error)
 	require.NoError(t, database.Create(&models.SaTask{ProjectID: project.ID, CreatedBy: 1, Title: "Archive notes", Description: "Move outdated notes.", Status: "done"}).Error)
 	require.NoError(t, database.Create(&models.SaAISession{ProjectID: project.ID, CreatedBy: 1, Title: "UI prototype critique", Context: "Discuss channel behavior."}).Error)
-	require.NoError(t, database.Create(&models.SaDocument{ProjectID: project.ID, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "Workbench principles.md", NormalizedName: "workbench principles.md", Extension: ".md", Revision: 1}).Error)
-	require.NoError(t, database.Create(&models.SaDocument{ProjectID: project.ID, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "Reference board.pdf", NormalizedName: "reference board.pdf", Extension: ".pdf", Revision: 1}).Error)
+	require.NoError(t, database.Create(&models.SaDocumentTree{ProjectID: project.ID, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "Workbench principles.md", NormalizedName: "workbench principles.md", Extension: ".md", Revision: 1}).Error)
+	require.NoError(t, database.Create(&models.SaDocumentTree{ProjectID: project.ID, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "Reference board.pdf", NormalizedName: "reference board.pdf", Extension: ".pdf", Revision: 1}).Error)
 	require.NoError(t, database.Create(&models.SaProjectChannel{ProjectID: project.ID, Title: "Roadmap Board", Icon: "link", URL: "https://example.com/roadmap-a1", SortOrder: 7}).Error)
 	require.NoError(t, database.Create(&models.SaProjectChannel{ProjectID: other.ID, Title: "Other Board", Icon: "link", URL: "https://example.com/other", SortOrder: 7}).Error)
 	require.NoError(t, database.Create(&models.SaCronPlan{ProjectID: project.ID, CreatedBy: 1, Title: "Weekly inbox review reminder", Schedule: "0 9 * * 1", NextRunAt: &nextRun, Enabled: true, LastResult: "Not run yet"}).Error)
diff --git a/backend/internal/logic/projects/workspace.go b/backend/internal/logic/projects/workspace.go
index a222bb0..f23e0ee 100644
--- a/backend/internal/logic/projects/workspace.go
+++ b/backend/internal/logic/projects/workspace.go
@@ -10,11 +10,11 @@ import (
 )
 
 type workspaceCounts struct {
-	inbox        int64
-	tasks        int64
-	aiSessions   int64
-	documents    int64
-	cronPlans    int64
+	inbox      int64
+	tasks      int64
+	aiSessions int64
+	documents  int64
+	cronPlans  int64
 }
 
 // Workspace 在确认项目归属后执行首屏聚合；后续子查询只接收已授权的内部主键。
@@ -90,7 +90,7 @@ func (s *Service) workspaceCounts(projectID uint) (workspaceCounts, error) {
 	if err := models.DBService.Model(&models.SaAISession{}).Where("project_id = ?", projectID).Count(&counts.aiSessions).Error; err != nil {
 		return counts, err
 	}
-	if err := models.DBService.Model(&models.SaDocument{}).Where("project_id = ?", projectID).Count(&counts.documents).Error; err != nil {
+	if err := models.DBService.Model(&models.SaDocumentTree{}).Where("project_id = ?", projectID).Count(&counts.documents).Error; err != nil {
 		return counts, err
 	}
 	if err := models.DBService.Model(&models.SaCronPlan{}).Where("project_id = ?", projectID).Count(&counts.cronPlans).Error; err != nil {
@@ -224,7 +224,7 @@ func (s *Service) workspaceAISessions(projectID uint, projectIdentity string) ([
 }
 
 func (s *Service) workspaceDocuments(projectID uint, projectIdentity string) ([]WorkspaceDocumentDTO, error) {
-	var documents []models.SaDocument
+	var documents []models.SaDocumentTree
 	if err := models.DBService.Where("project_id = ?", projectID).Order("updated_at desc, id desc").Limit(50).Find(&documents).Error; err != nil {
 		return nil, err
 	}
diff --git a/backend/internal/logic/projects/workspace_test.go b/backend/internal/logic/projects/workspace_test.go
index f5e26ed..227ce8f 100644
--- a/backend/internal/logic/projects/workspace_test.go
+++ b/backend/internal/logic/projects/workspace_test.go
@@ -33,8 +33,8 @@ func TestWorkspaceUsesIdentitiesUTCTimesAndProjectScopedTags(t *testing.T) {
 	inbox := models.SaInboxItem{ProjectID: project.ID, CreatedBy: 1, SourceType: "Manual", Title: "Collect notes", Body: "Turn research into tasks.", Status: "open", CreatedAt: createdAt, UpdatedAt: updatedAt}
 	task := models.SaTask{ProjectID: project.ID, CreatedBy: 1, TagID: &projectTag.ID, Title: "Confirm IA", Description: "Review channel layout.", Status: "done", DueAt: &nextRun, CreatedAt: createdAt, UpdatedAt: updatedAt}
 	session := models.SaAISession{ProjectID: project.ID, CreatedBy: 1, Title: "UI critique", Context: "Discuss channel behavior.", CreatedAt: createdAt, UpdatedAt: updatedAt}
-	firstDocument := models.SaDocument{ProjectID: project.ID, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "Workbench principles.md", NormalizedName: "workbench principles.md", Extension: ".md", MimeType: "text/markdown", Revision: 1, CreatedAt: createdAt, UpdatedAt: updatedAt}
-	secondDocument := models.SaDocument{ProjectID: project.ID, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "Reference board.pdf", NormalizedName: "reference board.pdf", Extension: ".pdf", MimeType: "application/pdf", Revision: 1, CreatedAt: createdAt, UpdatedAt: updatedAt}
+	firstDocument := models.SaDocumentTree{ProjectID: project.ID, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "Workbench principles.md", NormalizedName: "workbench principles.md", Extension: ".md", MimeType: "text/markdown", Revision: 1, CreatedAt: createdAt, UpdatedAt: updatedAt}
+	secondDocument := models.SaDocumentTree{ProjectID: project.ID, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "Reference board.pdf", NormalizedName: "reference board.pdf", Extension: ".pdf", MimeType: "application/pdf", Revision: 1, CreatedAt: createdAt, UpdatedAt: updatedAt}
 	channel := models.SaProjectChannel{ProjectID: project.ID, Title: "Roadmap Board", Icon: "link", URL: "https://example.com/roadmap", SortOrder: 7, CreatedAt: createdAt, UpdatedAt: updatedAt}
 	plan := models.SaCronPlan{ProjectID: project.ID, CreatedBy: 1, Title: "Weekly review", Schedule: "0 9 * * 1", NextRunAt: &nextRun, Enabled: true, CreatedAt: createdAt, UpdatedAt: updatedAt}
 	for _, record := range []any{&inbox, &task, &session, &firstDocument, &secondDocument, &channel, &plan} {
diff --git a/backend/internal/logic/search/service.go b/backend/internal/logic/search/service.go
index a3f39d0..641b010 100644
--- a/backend/internal/logic/search/service.go
+++ b/backend/internal/logic/search/service.go
@@ -92,7 +92,7 @@ func (s *Service) Search(userID uint, query string) ([]SearchResultDTO, error) {
 		})
 	}
 
-	var documents []models.SaDocument
+	var documents []models.SaDocumentTree
 	documentFilter := fmt.Sprintf(`(sa_projects.owner_id = ? OR EXISTS (
 			SELECT 1 FROM sa_task_shares
 			JOIN sa_tasks ON sa_tasks.id = sa_task_shares.task_id
diff --git a/backend/internal/logic/search/service_postgres_test.go b/backend/internal/logic/search/service_postgres_test.go
index 14f7896..b76c5ae 100644
--- a/backend/internal/logic/search/service_postgres_test.go
+++ b/backend/internal/logic/search/service_postgres_test.go
@@ -21,7 +21,7 @@ func TestPostgresSearchMatchesChinesePartialKeywords(t *testing.T) {
 	project := models.SaProject{OwnerID: owner.ID, Name: "中文回调平台", Identifier: "PG-CALLBACK"}
 	require.NoError(t, database.Create(&project).Error)
 	require.NoError(t, database.Create(&models.SaTask{ProjectID: project.ID, CreatedBy: owner.ID, Title: "回调任务", Status: "open"}).Error)
-	createPostgresSearchDocument(t, database, project, owner.ID, models.SaDocument{Name: "说明.md"}, "回调验签流程")
+	createPostgresSearchDocument(t, database, project, owner.ID, models.SaDocumentTree{Name: "说明.md"}, "回调验签流程")
 
 	results, err := NewService(database).Search(owner.ID, "回调")
 
@@ -38,8 +38,8 @@ func TestPostgresSearchKeepsAssignmentAndExplicitShareBoundaries(t *testing.T) {
 	assigned := models.SaTask{ProjectID: project.ID, CreatedBy: owner.ID, AssigneeID: &viewer.ID, Title: "边界词已指派", Status: "open"}
 	require.NoError(t, database.Create(&assigned).Error)
 	require.NoError(t, database.Create(&models.SaTask{ProjectID: project.ID, CreatedBy: owner.ID, Title: "边界词私有任务", Status: "open"}).Error)
-	sharedDocument := createPostgresSearchDocument(t, database, project, owner.ID, models.SaDocument{Name: "边界词共享笔记.md"}, "")
-	createPostgresSearchDocument(t, database, project, owner.ID, models.SaDocument{Name: "边界词私有笔记.md"}, "")
+	sharedDocument := createPostgresSearchDocument(t, database, project, owner.ID, models.SaDocumentTree{Name: "边界词共享笔记.md"}, "")
+	createPostgresSearchDocument(t, database, project, owner.ID, models.SaDocumentTree{Name: "边界词私有笔记.md"}, "")
 	require.NoError(t, database.Create(&models.SaTaskShare{TaskID: assigned.ID, ObjectType: "document", ObjectID: sharedDocument.ID}).Error)
 
 	results, err := NewService(database).Search(viewer.ID, "边界词")
@@ -70,7 +70,7 @@ func TestPostgresSearchUsesStableFairLimitAndRuneBoundedSnippets(t *testing.T) {
 			Status:    "open",
 			UpdatedAt: baseTime.Add(time.Duration(index) * time.Minute),
 		}).Error)
-		createPostgresSearchDocument(t, database, project, owner.ID, models.SaDocument{
+		createPostgresSearchDocument(t, database, project, owner.ID, models.SaDocumentTree{
 			Identity:  fmt.Sprintf("00000000-0000-7003-8000-%012d", index),
 			Name:      fmt.Sprintf("稳定排序笔记 %02d.md", index),
 			UpdatedAt: baseTime.Add(time.Duration(index) * time.Minute),
@@ -110,9 +110,9 @@ func createPostgresSearchDocument(
 	database *gorm.DB,
 	project models.SaProject,
 	ownerID uint,
-	document models.SaDocument,
+	document models.SaDocumentTree,
 	markdown string,
-) models.SaDocument {
+) models.SaDocumentTree {
 	t.Helper()
 	document.ProjectID = project.ID
 	document.ProjectIdentity = project.Identity
diff --git a/backend/internal/logic/search/service_test.go b/backend/internal/logic/search/service_test.go
index cc2ebaf..fc88ce4 100644
--- a/backend/internal/logic/search/service_test.go
+++ b/backend/internal/logic/search/service_test.go
@@ -52,7 +52,7 @@ func TestSearchAppliesStableFairGlobalLimitAcrossResultTypes(t *testing.T) {
 			Status:    "open",
 			UpdatedAt: baseTime.Add(time.Duration(index) * time.Minute),
 		}).Error)
-		document := models.SaDocument{
+		document := models.SaDocumentTree{
 			Identity:       fmt.Sprintf("00000000-0000-7003-8000-%012d", index),
 			ProjectID:      project.ID,
 			CreatedBy:      7,
@@ -136,9 +136,9 @@ func TestSearchOnlyReturnsNavigableProjectTaskAndDocumentResults(t *testing.T) {
 	require.Len(t, results, 3)
 }
 
-func createSearchDocument(t *testing.T, database *gorm.DB, projectID, userID uint, name, markdown, identity string, updatedAt time.Time) models.SaDocument {
+func createSearchDocument(t *testing.T, database *gorm.DB, projectID, userID uint, name, markdown, identity string, updatedAt time.Time) models.SaDocumentTree {
 	t.Helper()
-	document := models.SaDocument{
+	document := models.SaDocumentTree{
 		Identity: identity, ProjectID: projectID, CreatedBy: userID, Kind: models.DocumentKindFile,
 		Name: name, NormalizedName: strings.ToLower(name), Extension: ".md",
 		MimeType: "text/markdown", Size: int64(len([]byte(markdown))), Revision: 1,
diff --git a/backend/internal/logic/tasks/concurrency_postgres_test.go b/backend/internal/logic/tasks/concurrency_postgres_test.go
index 682b98e..24f99dc 100644
--- a/backend/internal/logic/tasks/concurrency_postgres_test.go
+++ b/backend/internal/logic/tasks/concurrency_postgres_test.go
@@ -29,7 +29,7 @@ func TestPostgresMovePreventsOldProjectShareFromBeingInsertedConcurrently(t *tes
 	require.NoError(t, database.Create(&first).Error)
 	require.NoError(t, database.Create(&second).Error)
 	task := models.SaTask{ProjectID: first.ID, CreatedBy: owner.ID, Title: "Move", Status: "open"}
-	document := models.SaDocument{ProjectID: first.ID, CreatedBy: owner.ID, Kind: models.DocumentKindFile, Name: "Old context.md", NormalizedName: "old context.md", Extension: ".md", Revision: 1}
+	document := models.SaDocumentTree{ProjectID: first.ID, CreatedBy: owner.ID, Kind: models.DocumentKindFile, Name: "Old context.md", NormalizedName: "old context.md", Extension: ".md", Revision: 1}
 	require.NoError(t, database.Create(&task).Error)
 	require.NoError(t, database.Create(&document).Error)
 	t.Cleanup(func() {
diff --git a/backend/internal/logic/tasks/handlers_test.go b/backend/internal/logic/tasks/handlers_test.go
index 857fcc4..cb41180 100644
--- a/backend/internal/logic/tasks/handlers_test.go
+++ b/backend/internal/logic/tasks/handlers_test.go
@@ -50,7 +50,7 @@ func TestTaskRegistrarMovesTaskByIdentityAndClearsForeignProjectTag(t *testing.T
 	require.NoError(t, database.Create(&tag).Error)
 	task := models.SaTask{ProjectID: first.ID, CreatedBy: 1, TagID: &tag.ID, Title: "迁移任务", Status: "open"}
 	require.NoError(t, database.Create(&task).Error)
-	document := models.SaDocument{ProjectID: first.ID, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "旧项目资料.md", NormalizedName: "旧项目资料.md", Extension: ".md", Revision: 1}
+	document := models.SaDocumentTree{ProjectID: first.ID, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "旧项目资料.md", NormalizedName: "旧项目资料.md", Extension: ".md", Revision: 1}
 	require.NoError(t, database.Create(&document).Error)
 	require.NoError(t, NewService(database).ShareObject(task.ID, "document", document.ID))
 	body := bytes.NewBufferString(fmt.Sprintf(`{"title":"迁移任务","description":"已移动","completed":false,"nextProjectId":%q}`, strings.ToUpper(second.Identity)))
diff --git a/backend/internal/logic/tasks/service.go b/backend/internal/logic/tasks/service.go
index 3135a9c..576cf17 100644
--- a/backend/internal/logic/tasks/service.go
+++ b/backend/internal/logic/tasks/service.go
@@ -269,7 +269,7 @@ func utcOptionalTime(value *time.Time) *time.Time {
 
 func ensureSharedObjectInProject(tx *gorm.DB, projectID uint, objectID uint) error {
 	var count int64
-	if err := tx.Model(&models.SaDocument{}).Where("id = ? AND project_id = ?", objectID, projectID).Count(&count).Error; err != nil {
+	if err := tx.Model(&models.SaDocumentTree{}).Where("id = ? AND project_id = ?", objectID, projectID).Count(&count).Error; err != nil {
 		return err
 	}
 	if count == 0 {
diff --git a/backend/internal/logic/tasks/service_test.go b/backend/internal/logic/tasks/service_test.go
index 535bdac..fe2719c 100644
--- a/backend/internal/logic/tasks/service_test.go
+++ b/backend/internal/logic/tasks/service_test.go
@@ -24,7 +24,7 @@ func TestUpdateLocksTaskBeforeProjectValidation(t *testing.T) {
 
 func TestShareObjectLocksTaskBeforeObjectValidation(t *testing.T) {
 	database, _, project, task := newTaskLockFixture(t)
-	document := models.SaDocument{ProjectID: project.ID, CreatedBy: task.CreatedBy, Kind: models.DocumentKindFile, Name: "Context.md", NormalizedName: "context.md", Extension: ".md", Revision: 1}
+	document := models.SaDocumentTree{ProjectID: project.ID, CreatedBy: task.CreatedBy, Kind: models.DocumentKindFile, Name: "Context.md", NormalizedName: "context.md", Extension: ".md", Revision: 1}
 	require.NoError(t, database.Create(&document).Error)
 	queries := captureTaskQueryOrder(t, database)
 
@@ -39,7 +39,7 @@ func TestAssigneeOnlySeesExplicitlySharedObjects(t *testing.T) {
 	database := newTestDB(t)
 	assigneeID := uint(2)
 	task := models.SaTask{ProjectID: 1, CreatedBy: 1, AssigneeID: &assigneeID, Title: "处理合同"}
-	document := models.SaDocument{ProjectID: 1, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "合同背景.md", NormalizedName: "合同背景.md", Extension: ".md", Revision: 1}
+	document := models.SaDocumentTree{ProjectID: 1, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "合同背景.md", NormalizedName: "合同背景.md", Extension: ".md", Revision: 1}
 	require.NoError(t, database.Create(&task).Error)
 	require.NoError(t, database.Create(&document).Error)
 	service := NewService()
@@ -68,7 +68,7 @@ func TestShareObjectRejectsUnsupportedType(t *testing.T) {
 func TestShareObjectRejectsObjectFromAnotherProject(t *testing.T) {
 	database := newTestDB(t)
 	task := models.SaTask{ProjectID: 1, CreatedBy: 1, Title: "Review"}
-	document := models.SaDocument{ProjectID: 2, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "Other project.md", NormalizedName: "other project.md", Extension: ".md", Revision: 1}
+	document := models.SaDocumentTree{ProjectID: 2, CreatedBy: 1, Kind: models.DocumentKindFile, Name: "Other project.md", NormalizedName: "other project.md", Extension: ".md", Revision: 1}
 	require.NoError(t, database.Create(&task).Error)
 	require.NoError(t, database.Create(&document).Error)
 	service := NewService()
diff --git a/backend/internal/models/document.go b/backend/internal/models/document_tree.go
similarity index 95%
rename from backend/internal/models/document.go
rename to backend/internal/models/document_tree.go
index ac0aca8..336f742 100644
--- a/backend/internal/models/document.go
+++ b/backend/internal/models/document_tree.go
@@ -11,7 +11,7 @@ const (
 	DocumentKindFile   = "file"
 )
 
-type SaDocument struct {
+type SaDocumentTree struct {
 	ID                      uint    `gorm:"primaryKey"`
 	Identity                string  `gorm:"type:char(36);uniqueIndex"`
 	ProjectID               uint    `gorm:"index;not null;uniqueIndex:uidx_sa_document_sibling,priority:1"`
@@ -37,6 +37,6 @@ type SaDocument struct {
 	DeletedAt               gorm.DeletedAt `gorm:"index"`
 }
 
-func (SaDocument) TableName() string {
+func (SaDocumentTree) TableName() string {
 	return "sa_documents"
 }
diff --git a/backend/internal/models/identity.go b/backend/internal/models/identity.go
index 0b13aca..71ff87f 100644
--- a/backend/internal/models/identity.go
+++ b/backend/internal/models/identity.go
@@ -75,7 +75,7 @@ func (m *SaTask) BeforeCreate(tx *gorm.DB) error {
 	return resolveOptionalIdentity(tx, &SaInboxItem{}, m.SourceInboxItemID, &m.SourceInboxItemIdentity)
 }
 
-func (m *SaDocument) BeforeCreate(tx *gorm.DB) error {
+func (m *SaDocumentTree) BeforeCreate(tx *gorm.DB) error {
 	if err := ensureIdentity(&m.Identity); err != nil {
 		return err
 	}
@@ -85,7 +85,7 @@ func (m *SaDocument) BeforeCreate(tx *gorm.DB) error {
 	if err := resolveIdentity(tx, &SaUser{}, m.CreatedBy, &m.CreatedByIdentity); err != nil {
 		return err
 	}
-	if err := resolveOptionalIdentity(tx, &SaDocument{}, m.ParentID, &m.ParentIdentity); err != nil {
+	if err := resolveOptionalIdentity(tx, &SaDocumentTree{}, m.ParentID, &m.ParentIdentity); err != nil {
 		return err
 	}
 	return resolveOptionalIdentity(tx, &SaInboxItem{}, m.SourceInboxItemID, &m.SourceInboxItemIdentity)
@@ -95,7 +95,7 @@ func (m *SaDocumentShare) BeforeCreate(tx *gorm.DB) error {
 	if err := ensureIdentity(&m.Identity); err != nil {
 		return err
 	}
-	if err := resolveIdentity(tx, &SaDocument{}, m.DocumentID, &m.DocumentIdentity); err != nil {
+	if err := resolveIdentity(tx, &SaDocumentTree{}, m.DocumentID, &m.DocumentIdentity); err != nil {
 		return err
 	}
 	return nil
@@ -234,7 +234,7 @@ func resolveEntityIdentity(tx *gorm.DB, entityType string, entityID uint, identi
 	case "task":
 		return resolveIdentity(tx, &SaTask{}, entityID, identity)
 	case "document":
-		return resolveIdentity(tx, &SaDocument{}, entityID, identity)
+		return resolveIdentity(tx, &SaDocumentTree{}, entityID, identity)
 	case "ai_session":
 		return resolveIdentity(tx, &SaAISession{}, entityID, identity)
 	case "tag":
diff --git a/backend/internal/models/new.go b/backend/internal/models/new.go
index 0c224cd..cdf99b4 100644
--- a/backend/internal/models/new.go
+++ b/backend/internal/models/new.go
@@ -36,7 +36,7 @@ func AutoMigrate(database *gorm.DB) error {
 		&SaInboxItem{},
 		&SaInboxSuggestion{},
 		&SaTask{},
-		&SaDocument{},
+		&SaDocumentTree{},
 		&SaDocumentContent{},
 		&SaDocumentBlob{},
 		&SaDocumentShare{},
diff --git a/backend/internal/seed/demo.go b/backend/internal/seed/demo.go
index 5f65e38..dbd4904 100644
--- a/backend/internal/seed/demo.go
+++ b/backend/internal/seed/demo.go
@@ -257,7 +257,7 @@ func firstOrCreateAISession(tx *gorm.DB, session models.SaAISession) error {
 }
 
 func firstOrCreateDocument(tx *gorm.DB, projectID, userID uint, name, markdown string) error {
-	var document models.SaDocument
+	var document models.SaDocumentTree
 	err := tx.Where("project_id = ? AND normalized_name = ?", projectID, strings.ToLower(name)).First(&document).Error
 	if err == nil {
 		return nil
@@ -265,7 +265,7 @@ func firstOrCreateDocument(tx *gorm.DB, projectID, userID uint, name, markdown s
 	if err != gorm.ErrRecordNotFound {
 		return err
 	}
-	document = models.SaDocument{
+	document = models.SaDocumentTree{
 		ProjectID: projectID, CreatedBy: userID, Kind: models.DocumentKindFile,
 		Name: name, NormalizedName: strings.ToLower(name), Extension: ".md",
 		MimeType: "text/markdown; charset=utf-8", Size: int64(len([]byte(markdown))),
diff --git a/backend/internal/seed/demo_postgres_test.go b/backend/internal/seed/demo_postgres_test.go
index 4042068..d6e5468 100644
--- a/backend/internal/seed/demo_postgres_test.go
+++ b/backend/internal/seed/demo_postgres_test.go
@@ -147,7 +147,7 @@ func TestPostgresDemoSeedSerializesConcurrentRunsForSameOwner(t *testing.T) {
 	assertPostgresDemoCount(t, database, &models.SaTask{}, "project_id IN ?", []any{projectIDs}, 6)
 	assertPostgresDemoCount(t, database, &models.SaInboxItem{}, "project_id IN ?", []any{projectIDs}, 7)
 	assertPostgresDemoCount(t, database, &models.SaAISession{}, "project_id = ?", []any{projects[0].ID}, 4)
-	assertPostgresDemoCount(t, database, &models.SaDocument{}, "project_id = ?", []any{projects[0].ID}, 2)
+	assertPostgresDemoCount(t, database, &models.SaDocumentTree{}, "project_id = ?", []any{projects[0].ID}, 2)
 	assertPostgresDemoCount(t, database, &models.SaCronPlan{}, "project_id = ?", []any{projects[0].ID}, 3)
 	assertPostgresDemoCount(t, database, &models.SaProjectChannel{}, "project_id = ?", []any{projects[0].ID}, 2)
 }
@@ -216,7 +216,7 @@ func cleanupPostgresDemoSeed(database *gorm.DB, userID uint) {
 		}
 		database.Where("project_id IN ?", projectIDs).Delete(&models.SaProjectEvent{})
 		database.Where("project_id IN ?", projectIDs).Delete(&models.SaTask{})
-		database.Where("project_id IN ?", projectIDs).Delete(&models.SaDocument{})
+		database.Where("project_id IN ?", projectIDs).Delete(&models.SaDocumentTree{})
 		database.Where("project_id IN ?", projectIDs).Delete(&models.SaAISession{})
 		database.Where("project_id IN ?", projectIDs).Delete(&models.SaTag{})
 		database.Where("project_id IN ?", projectIDs).Delete(&models.SaProjectChannel{})