Refactor: share nav drag and drop logic

Backend/internal/bootstrap/service.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"unicode"
 
 	"github.com/jackc/pgx/v5"
 
@@ -42,6 +43,8 @@ const (
 var (
 	ErrInstallationNotConfigured = errors.New("bootstrap installation step has not been completed")
 	ErrAdminNotConfigured        = errors.New("bootstrap admin step has not been completed")
+	ErrProjectNotFound           = errors.New("project not found")
+	ErrProjectFolderNotFound     = errors.New("project folder not found")
 )
 
 type Service struct {
@@ -177,6 +180,30 @@ type namedRecord struct {
 	Slug string `json:"slug"`
 }
 
+type ProjectHierarchyFolderRecord struct {
+	ID       string                         `json:"id"`
+	Label    string                         `json:"label"`
+	Children []ProjectHierarchyFolderRecord `json:"children"`
+}
+
+type CreateProjectFolderInput struct {
+	ProjectID      string
+	ParentFolderID string
+	Name           string
+}
+
+type CreateProjectFolderResult struct {
+	ProjectID     string                         `json:"projectId"`
+	CreatedFolder ProjectHierarchyFolderRecord   `json:"createdFolder"`
+	Folders       []ProjectHierarchyFolderRecord `json:"folders"`
+}
+
+type projectHierarchyFolderRow struct {
+	Path       string
+	ParentPath string
+	Label      string
+}
+
 func NewService(db *database.DB, posixRoot string) *Service {
 	return &Service{db: db, posixRoot: strings.TrimSpace(posixRoot)}
 }
@@ -794,6 +821,120 @@ func (service *Service) listProjects(ctx context.Context) ([]ProjectRecord, erro
 	return records, rows.Err()
 }
 
+func (service *Service) loadProjectByID(ctx context.Context, projectID string) (*ProjectRecord, error) {
+	var record ProjectRecord
+	err := service.db.Pool.QueryRow(ctx, `
+		SELECT id::text, organization_id::text, department_id::text, team_id::text, name, slug
+		FROM projects
+		WHERE id = $1::uuid
+		LIMIT 1;
+	`, projectID).Scan(&record.ID, &record.OrganizationID, &record.DepartmentID, &record.TeamID, &record.Name, &record.Slug)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, ErrProjectNotFound
+		}
+
+		return nil, err
+	}
+
+	return &record, nil
+}
+
+func (service *Service) GetProjectHierarchyFolders(ctx context.Context, projectID string) ([]ProjectHierarchyFolderRecord, error) {
+	return service.getProjectHierarchyFoldersByRootPath(ctx, projectID, projectHierarchyRootPath)
+}
+
+func (service *Service) GetProjectTreeFolders(ctx context.Context, projectID string) ([]ProjectHierarchyFolderRecord, error) {
+	return service.getProjectHierarchyFoldersByRootPath(ctx, projectID, projectTreeRootPath)
+}
+
+func (service *Service) getProjectHierarchyFoldersByRootPath(
+	ctx context.Context,
+	projectID string,
+	rootPath func(projectSlug string) string,
+) ([]ProjectHierarchyFolderRecord, error) {
+	project, err := service.loadProjectByID(ctx, projectID)
+	if err != nil {
+		return nil, err
+	}
+
+	rootParentPath := rootPath(project.Slug)
+
+	rows, err := service.db.Pool.Query(ctx, `
+		SELECT path, COALESCE(parent_path, ''), COALESCE(resource_name, '')
+		FROM posix_nodes
+		WHERE node_kind = 'directory'::posix_node_kind
+		  AND logical_type = 'hierarchy_folder'
+		  AND project_slug = $1
+		  AND path LIKE $2
+		ORDER BY depth ASC, path ASC;
+	`, project.Slug, rootParentPath+"/%")
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var folderRows []projectHierarchyFolderRow
+	for rows.Next() {
+		var row projectHierarchyFolderRow
+		if err := rows.Scan(&row.Path, &row.ParentPath, &row.Label); err != nil {
+			return nil, err
+		}
+		folderRows = append(folderRows, row)
+	}
+
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+
+	return buildProjectHierarchyFolderTree(folderRows, rootParentPath), nil
+}
+
+func (service *Service) CreateProjectFolder(ctx context.Context, input CreateProjectFolderInput) (CreateProjectFolderResult, error) {
+	return service.createProjectHierarchyFolder(ctx, input, projectHierarchyRootPath, service.createProjectHierarchyFolderOnDisk)
+}
+
+func (service *Service) CreateProjectTreeFolder(ctx context.Context, input CreateProjectFolderInput) (CreateProjectFolderResult, error) {
+	return service.createProjectHierarchyFolder(ctx, input, projectTreeRootPath, service.createProjectTreeFolderOnDisk)
+}
+
+func (service *Service) createProjectHierarchyFolder(
+	ctx context.Context,
+	input CreateProjectFolderInput,
+	rootPath func(projectSlug string) string,
+	createOnDisk func(projectSlug, parentFolderID, name string) (string, string, error),
+) (CreateProjectFolderResult, error) {
+	project, err := service.loadProjectByID(ctx, strings.TrimSpace(input.ProjectID))
+	if err != nil {
+		return CreateProjectFolderResult{}, err
+	}
+
+	createdPath, _, err := createOnDisk(project.Slug, strings.TrimSpace(input.ParentFolderID), input.Name)
+	if err != nil {
+		return CreateProjectFolderResult{}, err
+	}
+
+	if err := posixproj.NewProjector(service.db, service.posixRoot).Rebuild(ctx); err != nil {
+		return CreateProjectFolderResult{}, fmt.Errorf("rebuild POSIX projection: %w", err)
+	}
+
+	folders, err := service.getProjectHierarchyFoldersByRootPath(ctx, project.ID, rootPath)
+	if err != nil {
+		return CreateProjectFolderResult{}, err
+	}
+
+	createdFolder, ok := findProjectHierarchyFolder(folders, createdPath)
+	if !ok {
+		return CreateProjectFolderResult{}, fmt.Errorf("created project folder missing from projection")
+	}
+
+	return CreateProjectFolderResult{
+		ProjectID:     project.ID,
+		CreatedFolder: createdFolder,
+		Folders:       folders,
+	}, nil
+}
+
 func (service *Service) listWorkspaces(ctx context.Context) ([]WorkspaceRecord, error) {
 	rows, err := service.db.Pool.Query(ctx, `
 		SELECT id::text, organization_id::text, name, slug, kind::text, department_id::text, team_id::text, project_id::text
@@ -978,6 +1119,7 @@ func (service *Service) ensureBootstrapPOSIXSkeleton(
 		departmentPath,
 		teamPath,
 		projectPath,
+		filepath.Join(projectPath, "children"),
 		filepath.Join(projectPath, "tree"),
 		filepath.Join(usersPath, "personals"),
 	} {
@@ -1041,6 +1183,14 @@ func (service *Service) ensureBootstrapPOSIXSkeleton(
 		return fmt.Errorf("write project home.json: %w", err)
 	}
 
+	if err := writeJSONFile(filepath.Join(projectPath, "acl.json"), map[string]any{
+		"version":  1,
+		"inherits": true,
+		"rules":    []any{},
+	}); err != nil {
+		return fmt.Errorf("write project acl.json: %w", err)
+	}
+
 	if err := writeJSONFile(filepath.Join(usersPath, "settings.json"), map[string]any{
 		"primaryAdminId": admin.ID,
 	}); err != nil {
@@ -1060,6 +1210,207 @@ func (service *Service) ensureBootstrapPOSIXSkeleton(
 	return nil
 }
 
+func (service *Service) createProjectHierarchyFolderOnDisk(projectSlug, parentFolderID, name string) (string, string, error) {
+	return service.createProjectFolderOnDisk(projectSlug, parentFolderID, name, projectHierarchyRootPath)
+}
+
+func (service *Service) createProjectTreeFolderOnDisk(projectSlug, parentFolderID, name string) (string, string, error) {
+	return service.createProjectFolderOnDisk(projectSlug, parentFolderID, name, projectTreeRootPath)
+}
+
+func (service *Service) createProjectFolderOnDisk(
+	projectSlug, parentFolderID, name string,
+	rootPathBuilder func(projectSlug string) string,
+) (string, string, error) {
+	posixRoot := strings.TrimSpace(service.posixRoot)
+	if posixRoot == "" {
+		return "", "", fmt.Errorf("POSIX root is not configured")
+	}
+
+	trimmedName := strings.TrimSpace(name)
+	if trimmedName == "" {
+		return "", "", fmt.Errorf("folder name is required")
+	}
+
+	containerProjectionPath := rootPathBuilder(projectSlug)
+	parentDir := filepath.Join(posixRoot, filepath.FromSlash(containerProjectionPath))
+
+	if strings.TrimSpace(parentFolderID) != "" {
+		containerProjectionPath = filepath.ToSlash(filepath.Join(strings.TrimSpace(parentFolderID), "children"))
+		parentDir = filepath.Join(posixRoot, filepath.FromSlash(containerProjectionPath))
+		info, err := os.Stat(parentDir)
+		if err != nil {
+			if os.IsNotExist(err) {
+				return "", "", ErrProjectFolderNotFound
+			}
+			return "", "", fmt.Errorf("stat parent project folder: %w", err)
+		}
+		if !info.IsDir() {
+			return "", "", ErrProjectFolderNotFound
+		}
+	}
+
+	if err := os.MkdirAll(parentDir, 0o755); err != nil {
+		return "", "", fmt.Errorf("create parent project folder path: %w", err)
+	}
+
+	baseSlug := normalizePOSIXSlug(trimmedName)
+	folderName := slugDir("folder", baseSlug)
+	folderDir := filepath.Join(parentDir, folderName)
+	folderSlug := baseSlug
+
+	for attempt := 2; ; attempt += 1 {
+		if _, err := os.Stat(folderDir); os.IsNotExist(err) {
+			break
+		} else if err != nil {
+			return "", "", fmt.Errorf("stat candidate project folder: %w", err)
+		}
+
+		folderSlug = fmt.Sprintf("%s-%d", baseSlug, attempt)
+		folderName = slugDir("folder", folderSlug)
+		folderDir = filepath.Join(parentDir, folderName)
+	}
+
+	if err := os.MkdirAll(filepath.Join(folderDir, "children"), 0o755); err != nil {
+		return "", "", fmt.Errorf("create project hierarchy folder: %w", err)
+	}
+
+	if err := writeJSONFile(filepath.Join(folderDir, "folder.json"), map[string]any{
+		"name": trimmedName,
+		"slug": folderSlug,
+		"type": "folder",
+	}); err != nil {
+		return "", "", fmt.Errorf("write project folder.json: %w", err)
+	}
+
+	if err := writeJSONFile(filepath.Join(folderDir, "acl.json"), map[string]any{
+		"version":  1,
+		"inherits": true,
+		"rules":    []any{},
+	}); err != nil {
+		return "", "", fmt.Errorf("write project acl.json: %w", err)
+	}
+
+	return filepath.ToSlash(filepath.Join(containerProjectionPath, folderName)), folderSlug, nil
+}
+
+func buildProjectHierarchyFolderTree(rows []projectHierarchyFolderRow, rootParentPath string) []ProjectHierarchyFolderRecord {
+	if len(rows) == 0 {
+		return nil
+	}
+
+	nodesByPath := make(map[string]*ProjectHierarchyFolderRecord, len(rows))
+	childrenByParent := make(map[string][]string)
+
+	for _, row := range rows {
+		label := strings.TrimSpace(row.Label)
+		if label == "" {
+			label = fallbackFolderLabel(row.Path)
+		}
+		nodesByPath[row.Path] = &ProjectHierarchyFolderRecord{
+			ID:       row.Path,
+			Label:    label,
+			Children: []ProjectHierarchyFolderRecord{},
+		}
+		childrenByParent[row.ParentPath] = append(childrenByParent[row.ParentPath], row.Path)
+	}
+
+	var build func(parentPath string) []ProjectHierarchyFolderRecord
+	build = func(parentPath string) []ProjectHierarchyFolderRecord {
+		childPaths := childrenByParent[parentPath]
+		if len(childPaths) == 0 {
+			return nil
+		}
+
+		folders := make([]ProjectHierarchyFolderRecord, 0, len(childPaths))
+		for _, childPath := range childPaths {
+			node := nodesByPath[childPath]
+			if node == nil {
+				continue
+			}
+
+			folder := ProjectHierarchyFolderRecord{
+				ID:       node.ID,
+				Label:    node.Label,
+				Children: build(filepath.ToSlash(filepath.Join(childPath, "children"))),
+			}
+			folders = append(folders, folder)
+		}
+
+		return folders
+	}
+
+	return build(rootParentPath)
+}
+
+func findProjectHierarchyFolder(folders []ProjectHierarchyFolderRecord, folderID string) (ProjectHierarchyFolderRecord, bool) {
+	for _, folder := range folders {
+		if folder.ID == folderID {
+			return folder, true
+		}
+
+		if child, ok := findProjectHierarchyFolder(folder.Children, folderID); ok {
+			return child, true
+		}
+	}
+
+	return ProjectHierarchyFolderRecord{}, false
+}
+
+func projectHierarchyRootPath(projectSlug string) string {
+	return filepath.ToSlash(filepath.Join("projects", slugDir("project", projectSlug), "children"))
+}
+
+func projectTreeRootPath(projectSlug string) string {
+	return filepath.ToSlash(filepath.Join("projects", slugDir("project", projectSlug), "tree"))
+}
+
+func normalizePOSIXSlug(value string) string {
+	trimmed := strings.TrimSpace(strings.ToLower(value))
+	if trimmed == "" {
+		return "untitled"
+	}
+
+	var builder strings.Builder
+	lastDash := false
+	for _, r := range trimmed {
+		switch {
+		case unicode.IsLetter(r) || unicode.IsDigit(r):
+			builder.WriteRune(r)
+			lastDash = false
+		case r == '-' || r == '_' || unicode.IsSpace(r):
+			if !lastDash && builder.Len() > 0 {
+				builder.WriteByte('-')
+				lastDash = true
+			}
+		}
+	}
+
+	slug := strings.Trim(builder.String(), "-")
+	if slug == "" {
+		return "untitled"
+	}
+
+	return slug
+}
+
+func fallbackFolderLabel(path string) string {
+	base := filepath.Base(filepath.FromSlash(path))
+	trimmed := strings.TrimPrefix(base, "folder-")
+	parts := strings.FieldsFunc(trimmed, func(r rune) bool { return r == '-' || r == '_' })
+	for index, part := range parts {
+		if part == "" {
+			continue
+		}
+		parts[index] = strings.ToUpper(part[:1]) + part[1:]
+	}
+	label := strings.Join(parts, " ")
+	if label == "" {
+		return base
+	}
+	return label
+}
+
 func slugDir(prefix, slug string) string {
 	trimmedSlug := strings.TrimSpace(slug)
 	if trimmedSlug == "" {

Backend/internal/bootstrap/service_test.go

@@ -52,6 +52,8 @@ func TestEnsureBootstrapPOSIXSkeletonInitializesEmptyRoot(t *testing.T) {
 		filepath.Join(rootPath, "departments", "department-primary-department", "teams", "team-primary-team", "users.json"),
 		filepath.Join(rootPath, "projects", "project-primary-project", "settings.json"),
 		filepath.Join(rootPath, "projects", "project-primary-project", "home.json"),
+		filepath.Join(rootPath, "projects", "project-primary-project", "acl.json"),
+		filepath.Join(rootPath, "projects", "project-primary-project", "children"),
 		filepath.Join(rootPath, "projects", "project-primary-project", "tree"),
 		filepath.Join(rootPath, "users", "settings.json"),
 		filepath.Join(rootPath, "users", "data.json"),
@@ -90,12 +92,144 @@ func TestEnsureBootstrapPOSIXSkeletonInitializesEmptyRoot(t *testing.T) {
 		t.Fatalf("expected project settings type project, got %#v", projectSettings["type"])
 	}
 
+	projectACL := readJSONFileForTest[map[string]any](t, filepath.Join(rootPath, "projects", "project-primary-project", "acl.json"))
+	if projectACL["inherits"] != true {
+		t.Fatalf("expected project acl to inherit by default, got %#v", projectACL["inherits"])
+	}
+
 	usersSettings := readJSONFileForTest[map[string]any](t, filepath.Join(rootPath, "users", "settings.json"))
 	if usersSettings["primaryAdminId"] != "admin-1" {
 		t.Fatalf("expected primary admin id admin-1, got %#v", usersSettings["primaryAdminId"])
 	}
 }
 
+func TestCreateProjectHierarchyFolderOnDiskCreatesExpectedFolderShape(t *testing.T) {
+	rootPath := filepath.Join(t.TempDir(), "POSIX")
+	service := NewService(nil, rootPath)
+
+	err := service.ensureBootstrapPOSIXSkeleton(
+		InstallationRecord{ID: "installation-1", Name: "MangoPig", Mode: "personal", Access: "local", Protocol: "http", Host: "localhost", IsBootstrapped: true},
+		AdminSummary{ID: "admin-1", Email: "ronald@example.com", DisplayName: "Ronald"},
+		namedRecord{ID: "org-1", Name: "Primary Organization", Slug: "primary-organization"},
+		namedRecord{ID: "dept-1", Name: "Primary Department", Slug: "primary-department"},
+		namedRecord{ID: "team-1", Name: "Primary Team", Slug: "primary-team"},
+		namedRecord{ID: "project-1", Name: "Primary Project", Slug: "primary-project"},
+	)
+	if err != nil {
+		t.Fatalf("ensure bootstrap POSIX skeleton: %v", err)
+	}
+
+	createdPath, createdSlug, err := service.createProjectHierarchyFolderOnDisk("primary-project", "", "Design System")
+	if err != nil {
+		t.Fatalf("createProjectHierarchyFolderOnDisk root folder: %v", err)
+	}
+	if createdPath != "projects/project-primary-project/children/folder-design-system" {
+		t.Fatalf("unexpected created path: %s", createdPath)
+	}
+	if createdSlug != "design-system" {
+		t.Fatalf("unexpected created slug: %s", createdSlug)
+	}
+
+	createdFolderPath := filepath.Join(rootPath, "projects", "project-primary-project", "children", "folder-design-system")
+	for _, path := range []string{
+		filepath.Join(createdFolderPath, "folder.json"),
+		filepath.Join(createdFolderPath, "acl.json"),
+		filepath.Join(createdFolderPath, "children"),
+	} {
+		if _, err := os.Stat(path); err != nil {
+			t.Fatalf("expected path to exist %s: %v", path, err)
+		}
+	}
+
+	folderPayload := readJSONFileForTest[map[string]any](t, filepath.Join(createdFolderPath, "folder.json"))
+	if folderPayload["name"] != "Design System" {
+		t.Fatalf("expected folder name Design System, got %#v", folderPayload["name"])
+	}
+	if folderPayload["slug"] != "design-system" {
+		t.Fatalf("expected folder slug design-system, got %#v", folderPayload["slug"])
+	}
+
+	nestedPath, nestedSlug, err := service.createProjectHierarchyFolderOnDisk("primary-project", createdPath, "Research")
+	if err != nil {
+		t.Fatalf("createProjectHierarchyFolderOnDisk nested folder: %v", err)
+	}
+	if nestedPath != "projects/project-primary-project/children/folder-design-system/children/folder-research" {
+		t.Fatalf("unexpected nested path: %s", nestedPath)
+	}
+	if nestedSlug != "research" {
+		t.Fatalf("unexpected nested slug: %s", nestedSlug)
+	}
+}
+
+func TestCreateProjectTreeFolderOnDiskCreatesExpectedFolderShape(t *testing.T) {
+	rootPath := filepath.Join(t.TempDir(), "POSIX")
+	service := NewService(nil, rootPath)
+
+	err := service.ensureBootstrapPOSIXSkeleton(
+		InstallationRecord{ID: "installation-1", Name: "MangoPig", Mode: "personal", Access: "local", Protocol: "http", Host: "localhost", IsBootstrapped: true},
+		AdminSummary{ID: "admin-1", Email: "ronald@example.com", DisplayName: "Ronald"},
+		namedRecord{ID: "org-1", Name: "Primary Organization", Slug: "primary-organization"},
+		namedRecord{ID: "dept-1", Name: "Primary Department", Slug: "primary-department"},
+		namedRecord{ID: "team-1", Name: "Primary Team", Slug: "primary-team"},
+		namedRecord{ID: "project-1", Name: "Primary Project", Slug: "primary-project"},
+	)
+	if err != nil {
+		t.Fatalf("ensure bootstrap POSIX skeleton: %v", err)
+	}
+
+	createdPath, createdSlug, err := service.createProjectTreeFolderOnDisk("primary-project", "", "Docs")
+	if err != nil {
+		t.Fatalf("createProjectTreeFolderOnDisk root folder: %v", err)
+	}
+	if createdPath != "projects/project-primary-project/tree/folder-docs" {
+		t.Fatalf("unexpected created path: %s", createdPath)
+	}
+	if createdSlug != "docs" {
+		t.Fatalf("unexpected created slug: %s", createdSlug)
+	}
+
+	createdFolderPath := filepath.Join(rootPath, "projects", "project-primary-project", "tree", "folder-docs")
+	for _, path := range []string{
+		filepath.Join(createdFolderPath, "folder.json"),
+		filepath.Join(createdFolderPath, "acl.json"),
+		filepath.Join(createdFolderPath, "children"),
+	} {
+		if _, err := os.Stat(path); err != nil {
+			t.Fatalf("expected path to exist %s: %v", path, err)
+		}
+	}
+
+	nestedPath, nestedSlug, err := service.createProjectTreeFolderOnDisk("primary-project", createdPath, "Research")
+	if err != nil {
+		t.Fatalf("createProjectTreeFolderOnDisk nested folder: %v", err)
+	}
+	if nestedPath != "projects/project-primary-project/tree/folder-docs/children/folder-research" {
+		t.Fatalf("unexpected nested path: %s", nestedPath)
+	}
+	if nestedSlug != "research" {
+		t.Fatalf("unexpected nested slug: %s", nestedSlug)
+	}
+}
+
+func TestBuildProjectHierarchyFolderTreeBuildsNestedStructure(t *testing.T) {
+	rows := []projectHierarchyFolderRow{
+		{Path: "projects/project-primary-project/children/folder-design", ParentPath: projectHierarchyRootPath("primary-project"), Label: "Design"},
+		{Path: "projects/project-primary-project/children/folder-design/children/folder-research", ParentPath: "projects/project-primary-project/children/folder-design/children", Label: "Research"},
+		{Path: "projects/project-primary-project/children/folder-ops", ParentPath: projectHierarchyRootPath("primary-project"), Label: "Ops"},
+	}
+
+	folders := buildProjectHierarchyFolderTree(rows, projectHierarchyRootPath("primary-project"))
+	if len(folders) != 2 {
+		t.Fatalf("expected 2 top-level folders, got %d", len(folders))
+	}
+	if folders[0].Label != "Design" || folders[1].Label != "Ops" {
+		t.Fatalf("unexpected top-level folder labels: %#v", folders)
+	}
+	if len(folders[0].Children) != 1 || folders[0].Children[0].Label != "Research" {
+		t.Fatalf("unexpected nested folder structure: %#v", folders[0].Children)
+	}
+}
+
 func readJSONFileForTest[T any](t *testing.T, path string) T {
 	t.Helper()
 

Backend/internal/httpx/api_project_routes.go

@@ -0,0 +1,180 @@
+package httpx
+
+import (
+	"encoding/json"
+	"errors"
+	"io"
+	"net/http"
+	"strings"
+
+	bootstrapservice "moku-backend/internal/bootstrap"
+
+	"github.com/go-chi/chi/v5"
+)
+
+type createProjectFolderRequest struct {
+	Name           string `json:"name"`
+	ParentFolderID string `json:"parentFolderId"`
+}
+
+func (routes apiRoutes) handleProjectFolders(w http.ResponseWriter, r *http.Request) {
+	projectID := strings.TrimSpace(chi.URLParam(r, "projectId"))
+	if projectID == "" {
+		WriteError(w, http.StatusBadRequest, RequestIDFromContext(r.Context()), "invalid_request", "Project ID is required.")
+		return
+	}
+
+	folders, err := routes.bootstrapService().GetProjectHierarchyFolders(r.Context(), projectID)
+	if err != nil {
+		routes.writeProjectFolderError(w, r, err)
+		return
+	}
+
+	WriteJSON(w, http.StatusOK, map[string]any{
+		"data": map[string]any{
+			"projectId": projectID,
+			"folders":   folders,
+		},
+		"meta": map[string]any{
+			"resource": "project-folders",
+		},
+	})
+}
+
+func (routes apiRoutes) handleCreateProjectFolder(w http.ResponseWriter, r *http.Request) {
+	projectID := strings.TrimSpace(chi.URLParam(r, "projectId"))
+	if projectID == "" {
+		WriteError(w, http.StatusBadRequest, RequestIDFromContext(r.Context()), "invalid_request", "Project ID is required.")
+		return
+	}
+
+	payload, ok := decodeProjectFolderRequest(w, r)
+	if !ok {
+		return
+	}
+
+	payload.Name = strings.TrimSpace(payload.Name)
+	payload.ParentFolderID = strings.TrimSpace(payload.ParentFolderID)
+	if payload.Name == "" {
+		WriteError(w, http.StatusBadRequest, RequestIDFromContext(r.Context()), "invalid_request", "Folder name is required.")
+		return
+	}
+
+	result, err := routes.bootstrapService().CreateProjectFolder(r.Context(), bootstrapservice.CreateProjectFolderInput{
+		ProjectID:      projectID,
+		ParentFolderID: payload.ParentFolderID,
+		Name:           payload.Name,
+	})
+	if err != nil {
+		routes.writeProjectFolderError(w, r, err)
+		return
+	}
+
+	WriteJSON(w, http.StatusCreated, map[string]any{
+		"data": result,
+		"meta": map[string]any{
+			"resource":  "project-folder-create",
+			"persisted": true,
+		},
+	})
+}
+
+func (routes apiRoutes) handleProjectTreeFolders(w http.ResponseWriter, r *http.Request) {
+	projectID := strings.TrimSpace(chi.URLParam(r, "projectId"))
+	if projectID == "" {
+		WriteError(w, http.StatusBadRequest, RequestIDFromContext(r.Context()), "invalid_request", "Project ID is required.")
+		return
+	}
+
+	folders, err := routes.bootstrapService().GetProjectTreeFolders(r.Context(), projectID)
+	if err != nil {
+		routes.writeProjectFolderError(w, r, err)
+		return
+	}
+
+	WriteJSON(w, http.StatusOK, map[string]any{
+		"data": map[string]any{
+			"projectId": projectID,
+			"folders":   folders,
+		},
+		"meta": map[string]any{
+			"resource": "project-tree-folders",
+		},
+	})
+}
+
+func (routes apiRoutes) handleCreateProjectTreeFolder(w http.ResponseWriter, r *http.Request) {
+	projectID := strings.TrimSpace(chi.URLParam(r, "projectId"))
+	if projectID == "" {
+		WriteError(w, http.StatusBadRequest, RequestIDFromContext(r.Context()), "invalid_request", "Project ID is required.")
+		return
+	}
+
+	payload, ok := decodeProjectFolderRequest(w, r)
+	if !ok {
+		return
+	}
+
+	payload.Name = strings.TrimSpace(payload.Name)
+	payload.ParentFolderID = strings.TrimSpace(payload.ParentFolderID)
+	if payload.Name == "" {
+		WriteError(w, http.StatusBadRequest, RequestIDFromContext(r.Context()), "invalid_request", "Folder name is required.")
+		return
+	}
+
+	result, err := routes.bootstrapService().CreateProjectTreeFolder(r.Context(), bootstrapservice.CreateProjectFolderInput{
+		ProjectID:      projectID,
+		ParentFolderID: payload.ParentFolderID,
+		Name:           payload.Name,
+	})
+	if err != nil {
+		routes.writeProjectFolderError(w, r, err)
+		return
+	}
+
+	WriteJSON(w, http.StatusCreated, map[string]any{
+		"data": result,
+		"meta": map[string]any{
+			"resource":  "project-tree-folder-create",
+			"persisted": true,
+		},
+	})
+}
+
+func (routes apiRoutes) writeProjectFolderError(w http.ResponseWriter, r *http.Request, err error) {
+	switch {
+	case errors.Is(err, bootstrapservice.ErrProjectNotFound), errors.Is(err, bootstrapservice.ErrProjectFolderNotFound):
+		WriteError(w, http.StatusNotFound, RequestIDFromContext(r.Context()), "not_found", err.Error())
+	default:
+		routes.cfg.Logger.Error("persist project folder", "error", err, "path", r.URL.Path)
+		message := "Failed to persist project folder."
+		if routes.cfg.Config.IsDevelopment() {
+			message = message + " " + err.Error()
+		}
+		WriteError(w, http.StatusInternalServerError, RequestIDFromContext(r.Context()), "project_folder_persist_failed", message)
+	}
+}
+
+func decodeProjectFolderRequest(w http.ResponseWriter, r *http.Request) (createProjectFolderRequest, bool) {
+	var payload createProjectFolderRequest
+
+	decoder := json.NewDecoder(r.Body)
+	decoder.DisallowUnknownFields()
+
+	if err := decoder.Decode(&payload); err != nil {
+		if errors.Is(err, io.EOF) {
+			WriteError(w, http.StatusBadRequest, RequestIDFromContext(r.Context()), "invalid_json", "The request body is required and must be valid JSON.")
+			return payload, false
+		}
+
+		WriteError(w, http.StatusBadRequest, RequestIDFromContext(r.Context()), "invalid_json", "The request body must be valid JSON.")
+		return payload, false
+	}
+
+	if err := decoder.Decode(&struct{}{}); !errors.Is(err, io.EOF) {
+		WriteError(w, http.StatusBadRequest, RequestIDFromContext(r.Context()), "invalid_json", "The request body must contain a single JSON object.")
+		return payload, false
+	}
+
+	return payload, true
+}

Backend/internal/httpx/api_routes.go

@@ -33,6 +33,12 @@ func (routes apiRoutes) Register(router chi.Router) {
 		apiRouter.Get("/app-shell", routes.handleAppShellState)
 		apiRouter.Get("/organizations", routes.handleOrganizations)
 		apiRouter.Get("/workspaces", routes.handleWorkspaces)
+		apiRouter.Route("/projects/{projectId}", func(projectRouter chi.Router) {
+			projectRouter.Get("/folders", routes.handleProjectFolders)
+			projectRouter.Post("/folders", routes.handleCreateProjectFolder)
+			projectRouter.Get("/tree/folders", routes.handleProjectTreeFolders)
+			projectRouter.Post("/tree/folders", routes.handleCreateProjectTreeFolder)
+		})
 
 		if routes.cfg.Config.IsDevelopment() {
 			apiRouter.Post("/dev/bootstrap/reset", routes.handleDevelopmentBootstrapReset)

Backend/internal/posixproj/projector.go

@@ -321,18 +321,17 @@ func buildNode(rootPath, relPath string, entry fs.DirEntry, rootScope Scope) (No
 func deriveScope(relPath string, rootScope Scope) Scope {
 	scope := rootScope
 	parts := strings.Split(relPath, "/")
-	if len(parts) >= 2 && parts[0] == "departments" && strings.HasPrefix(parts[1], "department-") {
-		scope.DepartmentSlug = strings.TrimPrefix(parts[1], "department-")
-	}
-	if len(parts) >= 4 && parts[0] == "departments" && parts[2] == "teams" && strings.HasPrefix(parts[3], "team-") {
-		scope.DepartmentSlug = strings.TrimPrefix(parts[1], "department-")
-		scope.TeamSlug = strings.TrimPrefix(parts[3], "team-")
-	}
-	if len(parts) >= 2 && parts[0] == "projects" && strings.HasPrefix(parts[1], "project-") {
-		scope.ProjectSlug = strings.TrimPrefix(parts[1], "project-")
-	}
-	if len(parts) >= 3 && parts[0] == "users" && parts[1] == "personals" && strings.HasPrefix(parts[2], "personal-") {
-		scope.PersonalSlug = strings.TrimPrefix(parts[2], "personal-")
+	for _, part := range parts {
+		switch {
+		case strings.HasPrefix(part, "department-"):
+			scope.DepartmentSlug = strings.TrimPrefix(part, "department-")
+		case strings.HasPrefix(part, "team-"):
+			scope.TeamSlug = strings.TrimPrefix(part, "team-")
+		case strings.HasPrefix(part, "project-"):
+			scope.ProjectSlug = strings.TrimPrefix(part, "project-")
+		case strings.HasPrefix(part, "personal-"):
+			scope.PersonalSlug = strings.TrimPrefix(part, "personal-")
+		}
 	}
 	return scope
 }
@@ -344,6 +343,13 @@ func classifyPath(relPath string, isDir bool) (logicalType, fileRole string) {
 		fileRole = strings.TrimSuffix(name, filepath.Ext(name))
 	}
 
+	hasChildrenAncestor := pathContainsSegment(parts, "children")
+	hasTreeAncestor := pathContainsSegment(parts, "tree")
+	parentName := ""
+	if len(parts) >= 2 {
+		parentName = parts[len(parts)-2]
+	}
+
 	switch {
 	case relPath == "settings.json":
 		return "tenant", "settings"
@@ -392,27 +398,34 @@ func classifyPath(relPath string, isDir bool) (logicalType, fileRole string) {
 		return "department", fileRole
 	case len(parts) >= 2 && parts[0] == "projects" && strings.HasPrefix(parts[1], "project-"):
 		if isDir {
-			if len(parts) == 2 {
+			if strings.HasPrefix(name, "project-") {
 				return "project", ""
 			}
-			if len(parts) == 3 && parts[2] == "tree" {
+			if name == "children" {
+				return "project_children", ""
+			}
+			if name == "tree" {
 				return "project_tree", ""
 			}
-			if strings.Contains(relPath, "/tree/") || strings.HasSuffix(relPath, "/tree") {
-				if strings.HasPrefix(name, "folder-") {
-					return "folder", ""
-				}
-				if strings.HasPrefix(name, "item-") {
-					return "item", ""
-				}
+			if hasChildrenAncestor && strings.HasPrefix(name, "folder-") {
+				return "hierarchy_folder", ""
+			}
+			if hasTreeAncestor && strings.HasPrefix(name, "folder-") {
+				return "hierarchy_folder", ""
+			}
+			if hasTreeAncestor && strings.HasPrefix(name, "item-") {
+				return "item", ""
 			}
 		}
-		if strings.Contains(relPath, "/tree/") {
-			if strings.HasPrefix(parts[len(parts)-2], "item-") {
+		if hasChildrenAncestor && strings.HasPrefix(parentName, "folder-") {
+			return "hierarchy_folder", fileRole
+		}
+		if hasTreeAncestor {
+			if strings.HasPrefix(parentName, "item-") {
 				return "item", fileRole
 			}
-			if strings.HasPrefix(parts[len(parts)-2], "folder-") {
-				return "folder", fileRole
+			if strings.HasPrefix(parentName, "folder-") {
+				return "hierarchy_folder", fileRole
 			}
 		}
 		return "project", fileRole
@@ -456,6 +469,15 @@ func classifyPath(relPath string, isDir bool) (logicalType, fileRole string) {
 	}
 }
 
+func pathContainsSegment(parts []string, target string) bool {
+	for _, part := range parts {
+		if part == target {
+			return true
+		}
+	}
+	return false
+}
+
 func projectionParentPath(relPath string) *string {
 	if relPath == "" || relPath == rootProjectionPath {
 		return nil

Backend/internal/posixproj/projector_test.go

@@ -13,7 +13,11 @@ func TestScanRootBuildsProjectedNodesFromBootstrapShape(t *testing.T) {
 	mustMkdirAll(t, filepath.Join(root, "catalog", "packs"))
 	mustMkdirAll(t, filepath.Join(root, "catalog", "standalone"))
 	mustMkdirAll(t, filepath.Join(root, "departments", "department-primary-department", "teams", "team-primary-team"))
+	mustMkdirAll(t, filepath.Join(root, "projects", "project-primary-project", "children", "folder-design", "children", "project-web", "children"))
+	mustMkdirAll(t, filepath.Join(root, "projects", "project-primary-project", "children", "folder-design", "children", "project-web", "tree"))
 	mustMkdirAll(t, filepath.Join(root, "projects", "project-primary-project", "tree"))
+	mustMkdirAll(t, filepath.Join(root, "projects", "project-primary-project", "tree", "folder-docs", "children"))
+	mustMkdirAll(t, filepath.Join(root, "projects", "project-primary-project", "tree", "folder-docs", "item-roadmap"))
 	mustMkdirAll(t, filepath.Join(root, "users", "personals"))
 
 	mustWriteJSON(t, filepath.Join(root, "settings.json"), map[string]any{
@@ -57,6 +61,48 @@ func TestScanRootBuildsProjectedNodesFromBootstrapShape(t *testing.T) {
 		"type":    "project-home",
 		"project": "primary-project",
 	})
+	mustWriteJSON(t, filepath.Join(root, "projects", "project-primary-project", "acl.json"), map[string]any{
+		"inherits": true,
+		"rules":    []any{},
+	})
+	mustWriteJSON(t, filepath.Join(root, "projects", "project-primary-project", "children", "folder-design", "folder.json"), map[string]any{
+		"name": "Design",
+		"slug": "design",
+	})
+	mustWriteJSON(t, filepath.Join(root, "projects", "project-primary-project", "children", "folder-design", "acl.json"), map[string]any{
+		"inherits": true,
+		"rules":    []any{},
+	})
+	mustWriteJSON(t, filepath.Join(root, "projects", "project-primary-project", "children", "folder-design", "children", "project-web", "settings.json"), map[string]any{
+		"id":   "project-2",
+		"name": "Web Project",
+		"slug": "web",
+		"type": "project",
+	})
+	mustWriteJSON(t, filepath.Join(root, "projects", "project-primary-project", "children", "folder-design", "children", "project-web", "home.json"), map[string]any{
+		"type":    "project-home",
+		"project": "web",
+	})
+	mustWriteJSON(t, filepath.Join(root, "projects", "project-primary-project", "children", "folder-design", "children", "project-web", "acl.json"), map[string]any{
+		"inherits": true,
+		"rules":    []any{},
+	})
+	mustWriteJSON(t, filepath.Join(root, "projects", "project-primary-project", "tree", "folder-docs", "folder.json"), map[string]any{
+		"name": "Docs",
+		"slug": "docs",
+	})
+	mustWriteJSON(t, filepath.Join(root, "projects", "project-primary-project", "tree", "folder-docs", "item-roadmap", "item.json"), map[string]any{
+		"id":   "item-1",
+		"name": "Roadmap",
+		"slug": "roadmap",
+		"type": "board",
+	})
+	mustWriteJSON(t, filepath.Join(root, "projects", "project-primary-project", "tree", "folder-docs", "item-roadmap", "schema.json"), map[string]any{
+		"type": "object",
+	})
+	mustWriteJSON(t, filepath.Join(root, "projects", "project-primary-project", "tree", "folder-docs", "item-roadmap", "data.json"), map[string]any{
+		"title": "Roadmap",
+	})
 	mustWriteJSON(t, filepath.Join(root, "users", "settings.json"), map[string]any{
 		"primaryAdminId": "admin-1",
 	})
@@ -119,6 +165,44 @@ func TestScanRootBuildsProjectedNodesFromBootstrapShape(t *testing.T) {
 		t.Fatalf("unexpected project tree node: %#v", projectTree)
 	}
 
+	projectChildren := index["projects/project-primary-project/children"]
+	if projectChildren.LogicalType != "project_children" || projectChildren.NodeKind != NodeKindDirectory {
+		t.Fatalf("unexpected project children node: %#v", projectChildren)
+	}
+
+	hierarchyFolder := index["projects/project-primary-project/children/folder-design"]
+	if hierarchyFolder.LogicalType != "hierarchy_folder" || hierarchyFolder.ProjectSlug != "primary-project" {
+		t.Fatalf("unexpected hierarchy folder node: %#v", hierarchyFolder)
+	}
+
+	hierarchyFolderACL := index["projects/project-primary-project/children/folder-design/acl.json"]
+	if hierarchyFolderACL.LogicalType != "hierarchy_folder" || hierarchyFolderACL.FileRole != "acl" {
+		t.Fatalf("unexpected hierarchy folder acl classification: %#v", hierarchyFolderACL)
+	}
+
+	childProjectSettings := index["projects/project-primary-project/children/folder-design/children/project-web/settings.json"]
+	if childProjectSettings.LogicalType != "project" || childProjectSettings.ProjectSlug != "web" {
+		t.Fatalf("unexpected child project classification: %#v", childProjectSettings)
+	}
+
+	treeFolder := index["projects/project-primary-project/tree/folder-docs"]
+	if treeFolder.LogicalType != "hierarchy_folder" || treeFolder.ProjectSlug != "primary-project" {
+		t.Fatalf("unexpected tree folder node: %#v", treeFolder)
+	}
+
+	treeFolderACL := index["projects/project-primary-project/tree/folder-docs/folder.json"]
+	if treeFolderACL.LogicalType != "hierarchy_folder" || treeFolderACL.FileRole != "folder" {
+		t.Fatalf("unexpected tree folder file classification: %#v", treeFolderACL)
+	}
+
+	treeItem := index["projects/project-primary-project/tree/folder-docs/item-roadmap/item.json"]
+	if treeItem.LogicalType != "item" || treeItem.FileRole != "item" {
+		t.Fatalf("unexpected tree item classification: %#v", treeItem)
+	}
+	if treeItem.ResourceSlug != "roadmap" {
+		t.Fatalf("expected tree item resource slug roadmap, got %#v", treeItem.ResourceSlug)
+	}
+
 	usersData := index["users/data.json"]
 	if usersData.LogicalType != "users" || usersData.FileRole != "data" {
 		t.Fatalf("unexpected users data classification: %#v", usersData)

Documentation/POSIX-Structure.md

@@ -1,5 +1,7 @@
 # POSIX Structure
 
+[Filetree Link](https://tree.nathanfriend.com/?s=(%27optiUs!(%27fancy!Yue~fullPath!fbq~YailingSlash!Yue~rootDot!fbq)~R(%27R%27PJ%20or%20OrganizatiU%20%7Bqrver%7DM*46layout6cNlog7packs7*pack37A2*enYies75W5A_standbUe7WA6HwH30LZ2teamw5teamGL5Z6FwF30LKTC058T5C7XFG5LXKXTXC7XI7I05QG5BN2*8QG5BN6Z04_dN_pJw*pJGlayout2L*KI70%27)~vEiU!%271%27)*%20%200M52_*3-%3Cslug%3E4qttings5**69M*7%2F08VG*V259.jsUA5manifestBQ25*schema25*dCchildrenEersFprojectG305HdepartmentI*YeeJEUbKhome2L*42M%5CnNataQitemRsource!Tacl2UonVfolderW*app37X55YtrZusE_90balqsews0%01wqb_ZYXWVUTRQNMLKJIHGFECBA987654320*)
+
 ``` markdown
 Personal or Organization (server)/
 ├── settings.json
@@ -26,6 +28,18 @@ Personal or Organization (server)/
 │   └── project-<slug>/
 │       ├── settings.json
 │       ├── home.json
+│       ├── acl.json
+│       ├── children/
+│       │   └── folder-<slug>/
+│       │       ├── folder.json
+│       │       ├── acl.json
+│       │       └── children/
+│       │           └── project-<slug>/
+│       │               ├── settings.json
+│       │               ├── home.json
+│       │               ├── acl.json
+│       │               ├── children/
+│       │               └── tree/
 │       └── tree/
 │           ├── item-<slug>/
 │           │   ├── item.json

Frontend/src/components/shell/ProjectSelector/ProjectSelector.module.scss

@@ -1,3 +1,5 @@
+@use "../shared/tree-nav" as treeNav;
+
 .root {
   display: grid;
   --project-drawer-gap: var(--space-3);
@@ -191,142 +193,126 @@
 }
 
 .treeSectionLabel {
-  @include text-caption;
-  margin: 0 0 var(--space-2);
+	@include treeNav.section-label;
+  margin: 0;
   padding: 0 var(--space-3);
-  color: var(--color-text-subtle);
-  text-transform: uppercase;
-  letter-spacing: 0.04em;
 }
 
-.treeList {
-  list-style: none;
-  display: grid;
-  gap: var(--space-1);
-  padding: 0;
-}
-
-.treeEmptySlot {
-	min-height: calc(var(--control-size-lg) - var(--space-2));
-	padding-left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
-	border-radius: var(--radius-lg);
-	border: 1px dashed color-mix(in srgb, var(--color-border) 38%, transparent);
-	opacity: 0.35;
-}
-
-.treeInputRow {
-	width: 100%;
-	min-width: 0;
-	display: grid;
-	grid-template-columns: auto minmax(0, 1fr);
+.treeSectionHeader {
+	display: flex;
 	align-items: center;
+	justify-content: space-between;
 	gap: var(--space-2);
-	min-height: calc(var(--control-size-lg) - var(--space-2));
-	padding: var(--space-2) var(--space-3);
-	padding-left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
-	border: 1px solid color-mix(in srgb, var(--color-border) 42%, transparent);
-	border-radius: var(--radius-lg);
-	background: color-mix(in srgb, var(--color-surface) 94%, transparent);
+	margin-bottom: var(--space-2);
+	padding-right: var(--space-1);
 }
 
-.treeInput {
-	width: 100%;
-	min-width: 0;
-	border: 0;
-	background: transparent;
+.treeControls {
+	display: inline-flex;
+	align-items: center;
+	gap: var(--space-1);
+	flex-wrap: wrap;
+	justify-content: flex-end;
+}
+
+.treeControlButton {
+	display: inline-flex;
+	align-items: center;
+	justify-content: center;
+	width: calc(var(--control-size-md) - var(--space-1));
+	height: calc(var(--control-size-md) - var(--space-1));
+	@include text-caption;
+	padding: 0;
+	border: 1px solid color-mix(in srgb, var(--color-border) 46%, transparent);
+	border-radius: var(--radius-pill);
+	background: color-mix(in srgb, var(--color-surface) 95%, transparent);
+	color: var(--color-text-muted);
+	transition:
+		border-color 160ms var(--easing-standard),
+		background 160ms var(--easing-standard),
+		color 160ms var(--easing-standard);
+}
+
+.treeControlButton:hover,
+.treeControlButton:focus-visible {
+	border-color: color-mix(in srgb, var(--color-border-strong) 56%, transparent);
+	background: var(--color-surface-hover);
 	color: var(--color-text);
-	font: inherit;
 	outline: none;
 }
 
-.treeInput::placeholder {
-	color: var(--color-text-muted);
+.treeControlButton:disabled {
+	opacity: 0.45;
+	cursor: default;
+}
+
+.treeList {
+	@include treeNav.tree-list;
+}
+
+.treeEmptySlot {
+	@include treeNav.empty-slot;
+}
+
+.treeInputRow {
+	@include treeNav.input-row;
+}
+
+.treeInput {
+	@include treeNav.input;
 }
 
 .treeItem {
-  width: 100%;
-  min-width: 0;
-  display: grid;
-  grid-template-columns: auto auto minmax(0, 1fr) auto;
-  align-items: center;
-  gap: var(--space-2);
-  min-height: calc(var(--control-size-lg) - var(--space-2));
-  padding: var(--space-2) var(--space-3);
-  padding-left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
-  border: 1px solid transparent;
-  border-radius: var(--radius-lg);
-  background: transparent;
-  color: var(--color-text-muted);
-  transition:
-    background 160ms var(--easing-standard),
-    color 160ms var(--easing-standard),
-    border-color 160ms var(--easing-standard),
-    box-shadow 160ms var(--easing-standard),
-    transform 180ms var(--easing-standard);
-  text-align: left;
+	@include treeNav.item;
 }
 
 .treeItem:hover,
 .treeItem:focus-visible {
-  background: color-mix(in srgb, var(--color-surface-hover) 80%, var(--color-accent-soft) 20%);
-  color: var(--color-text);
-  box-shadow: inset 0 1px 0 color-mix(in srgb, white 4%, transparent);
+	@include treeNav.item-hover;
 }
 
 .treeItemFolder {
-  color: var(--color-text);
+	@include treeNav.item-folder;
 }
 
 .treeItemDragging {
-	opacity: 0.45;
-	transform: scale(0.985);
-	box-shadow: none;
+	@include treeNav.item-dragging;
 }
 
 .treeItemDropBefore {
-	box-shadow: inset 0 2px 0 color-mix(in srgb, var(--color-accent-strong) 78%, transparent);
+	@include treeNav.item-drop-before;
 }
 
 .treeItemDropAfter {
-	box-shadow: inset 0 -2px 0 color-mix(in srgb, var(--color-accent-strong) 78%, transparent);
+	@include treeNav.item-drop-after;
 }
 
 .treeItemDropInside {
-	border-color: color-mix(in srgb, var(--color-accent-strong) 55%, transparent);
-	background: color-mix(in srgb, var(--color-accent-soft) 36%, var(--color-surface));
-	color: var(--color-text);
-	box-shadow: inset 0 1px 0 color-mix(in srgb, white 4%, transparent);
+	@include treeNav.item-drop-inside;
 }
 
 .folderChevron {
-  color: var(--color-text-muted);
-  transition: transform 160ms var(--easing-standard);
+	@include treeNav.folder-chevron;
 }
 
 .folderChevronOpen {
-  transform: rotate(90deg);
+	@include treeNav.folder-chevron-open;
 }
 
 .treeItemActive {
-  border-color: var(--color-border);
-  background: var(--color-surface);
-  color: var(--color-text);
-  box-shadow: inset 0 1px 0 color-mix(in srgb, white 4%, transparent);
+	@include treeNav.item-active;
 }
 
 .icon {
-  color: inherit;
-  opacity: 0.85;
+	@include treeNav.icon;
 }
 
 .label {
-  @include text-label;
-  min-width: 0;
+	@include treeNav.label;
 }
 
 .itemMeta {
-  @include text-caption;
-  color: var(--color-text-muted);
+	@include treeNav.item-meta;
 }
 
 @media (max-width: 720px) {

Frontend/src/components/shell/ProjectSelector/ProjectSelector.tsx

@@ -1,9 +1,21 @@
 // Path: Frontend/src/components/shell/ProjectSelector/ProjectSelector.tsx
 
 import { For, Show, createEffect, createSignal, onCleanup, onMount, type JSX } from "solid-js";
-import { ChevronDown, ChevronRight, Folder, LayoutGrid } from "../../../lib/icons";
+import { ChevronDown, ChevronRight, Folder, LayoutGrid, ListCollapse, UnfoldVertical } from "../../../lib/icons";
 import { ProjectContextMenu } from "../ProjectContextMenu/ProjectContextMenu";
 import { useAppShellData } from "../data/app-shell.context";
+import { resolveAPIBase } from "../../../lib/api";
+import {
+	collectBranchNodeIds,
+	findTreeNodeDepth,
+	findTreeNodeLocation,
+	getPointerRelativeY,
+	isUuidString,
+	moveTreeNode,
+	resolveTreeDropTarget,
+	type NavTreeAdapter,
+	type NavTreeDropTarget,
+} from "../shared/navTreeDnd";
 import {
 	createProjectFolderTarget,
 	createProjectSurfaceTarget,
@@ -36,244 +48,70 @@ type ProjectLeafNode = {
 
 type ProjectTreeNode = ProjectFolderNode | ProjectLeafNode;
 
+type PersistedProjectFolderRecord = {
+	id: string;
+	label: string;
+	children: PersistedProjectFolderRecord[];
+};
+
+type ProjectFoldersResponse = {
+	data?: {
+		folders?: PersistedProjectFolderRecord[];
+	};
+	error?: string;
+	message?: string;
+};
+
 type PendingProjectFolderDraft = {
 	parentId: string | null;
 	depth: number;
 };
 
-type ProjectDragTarget = {
-	parentId: string | null;
-	index: number;
-	intent: "before" | "after" | "inside";
-	targetNodeId?: string;
-};
+type ProjectDragTarget = NavTreeDropTarget;
 
 type ProjectDragState = {
 	draggedNodeId: string;
 	dropTarget: ProjectDragTarget | null;
 };
 
-type ProjectNodeLocation = {
-	parentId: string | null;
-	index: number;
-	node: ProjectTreeNode;
-};
-
 const LONG_PRESS_MS = 320;
 
-const createProjectFolderId = (): string => `project-folder-${Math.random().toString(36).slice(2, 10)}`;
-
 const getProjectTreeNodeId = (node: ProjectTreeNode): string =>
 	node.kind === "folder" ? node.id : node.item.id;
 
-const buildProjectTree = (items: readonly ProjectItem[]): ProjectTreeNode[] =>
-	items.map((item) => ({
-		kind: "project",
-		item,
+const buildPersistedFolderNodes = (folders: readonly PersistedProjectFolderRecord[] = []): ProjectTreeNode[] =>
+	folders.map((folder) => ({
+		kind: "folder",
+		id: folder.id,
+		label: folder.label,
+		children: buildPersistedFolderNodes(folder.children ?? []),
 	}));
 
-const cloneProjectTreeNode = (node: ProjectTreeNode): ProjectTreeNode => {
-	if (node.kind === "project") {
-		return {
-			kind: "project",
-			item: { ...node.item },
-		};
-	}
+const buildProjectTree = (
+	items: readonly ProjectItem[],
+	folders: readonly PersistedProjectFolderRecord[] = [],
+): ProjectTreeNode[] => [
+	...items.map((item) => ({
+		kind: "project" as const,
+		item,
+	})),
+	...buildPersistedFolderNodes(folders),
+];
 
-	return {
-		kind: "folder",
-		id: node.id,
-		label: node.label,
-		meta: node.meta,
-		children: node.children.map(cloneProjectTreeNode),
-	};
-};
+const readPersistedFolders = (body: ProjectFoldersResponse): PersistedProjectFolderRecord[] =>
+	Array.isArray(body.data?.folders) ? body.data.folders : [];
 
-const insertProjectFolderNode = (
-	nodes: readonly ProjectTreeNode[],
-	parentId: string | null,
-	folder: ProjectFolderNode,
-): ProjectTreeNode[] => {
-	if (parentId === null) {
-		return [...nodes, folder];
-	}
-
-	return nodes.map((node) => {
-		if (node.kind !== "folder") {
-			return node;
-		}
-
-		if (node.id === parentId) {
-			return {
+const projectTreeAdapter: NavTreeAdapter<ProjectTreeNode> = {
+	getNodeId: getProjectTreeNodeId,
+	isBranchNode: (node) => node.kind === "folder",
+	getChildren: (node) => (node.kind === "folder" ? node.children : []),
+	withChildren: (node, children) =>
+		node.kind === "folder"
+			? {
 				...node,
-				children: [...node.children, folder],
-			};
-		}
-
-		return {
-			...node,
-			children: insertProjectFolderNode(node.children, parentId, folder),
-		};
-	});
-};
-
-const findProjectNodeLocation = (
-	nodes: readonly ProjectTreeNode[],
-	nodeId: string,
-	parentId: string | null = null,
-): ProjectNodeLocation | null => {
-	for (let index = 0; index < nodes.length; index += 1) {
-		const node = nodes[index];
-
-		if (getProjectTreeNodeId(node) === nodeId) {
-			return { parentId, index, node };
-		}
-
-		if (node.kind === "folder") {
-			const nestedLocation = findProjectNodeLocation(node.children, nodeId, node.id);
-
-			if (nestedLocation) {
-				return nestedLocation;
+				children: [...children],
 			}
-		}
-	}
-
-	return null;
-};
-
-const findProjectNodeDepth = (nodes: readonly ProjectTreeNode[], nodeId: string, depth = 0): number | null => {
-	for (const node of nodes) {
-		if (getProjectTreeNodeId(node) === nodeId) {
-			return depth;
-		}
-
-		if (node.kind === "folder") {
-			const nestedDepth = findProjectNodeDepth(node.children, nodeId, depth + 1);
-
-			if (nestedDepth !== null) {
-				return nestedDepth;
-			}
-		}
-	}
-
-	return null;
-};
-
-const projectTreeContainsNode = (nodes: readonly ProjectTreeNode[], nodeId: string): boolean => {
-	for (const node of nodes) {
-		if (getProjectTreeNodeId(node) === nodeId) {
-			return true;
-		}
-
-		if (node.kind === "folder" && projectTreeContainsNode(node.children, nodeId)) {
-			return true;
-		}
-	}
-
-	return false;
-};
-
-const removeProjectTreeNode = (
-	nodes: readonly ProjectTreeNode[],
-	nodeId: string,
-): { nodes: ProjectTreeNode[]; removed: ProjectTreeNode | null } => {
-	const nextNodes: ProjectTreeNode[] = [];
-	let removed: ProjectTreeNode | null = null;
-
-	for (const node of nodes) {
-		if (getProjectTreeNodeId(node) === nodeId) {
-			removed = node;
-			continue;
-		}
-
-		if (node.kind === "folder") {
-			const result = removeProjectTreeNode(node.children, nodeId);
-
-			if (result.removed) {
-				removed = result.removed;
-				nextNodes.push({
-					...node,
-					children: result.nodes,
-				});
-				continue;
-			}
-		}
-
-		nextNodes.push(node);
-	}
-
-	return { nodes: nextNodes, removed };
-};
-
-const insertProjectTreeNode = (
-	nodes: readonly ProjectTreeNode[],
-	parentId: string | null,
-	index: number,
-	nodeToInsert: ProjectTreeNode,
-): ProjectTreeNode[] => {
-	if (parentId === null) {
-		const nextNodes = [...nodes];
-		nextNodes.splice(Math.max(0, Math.min(index, nextNodes.length)), 0, nodeToInsert);
-		return nextNodes;
-	}
-
-	return nodes.map((node) => {
-		if (node.kind !== "folder") {
-			return node;
-		}
-
-		if (node.id === parentId) {
-			const nextChildren = [...node.children];
-			nextChildren.splice(Math.max(0, Math.min(index, nextChildren.length)), 0, nodeToInsert);
-			return {
-				...node,
-				children: nextChildren,
-			};
-		}
-
-		return {
-			...node,
-			children: insertProjectTreeNode(node.children, parentId, index, nodeToInsert),
-		};
-	});
-};
-
-const moveProjectTreeNode = (
-	nodes: readonly ProjectTreeNode[],
-	draggedNodeId: string,
-	dropTarget: ProjectDragTarget,
-): ProjectTreeNode[] => {
-	const location = findProjectNodeLocation(nodes, draggedNodeId);
-
-	if (!location) {
-		return [...nodes];
-	}
-
-	if (
-		location.node.kind === "folder" &&
-		dropTarget.parentId !== null &&
-		(projectTreeContainsNode(location.node.children, dropTarget.parentId) || dropTarget.parentId === location.node.id)
-	) {
-		return [...nodes];
-	}
-
-	let normalizedIndex = dropTarget.index;
-
-	if (dropTarget.parentId === location.parentId && dropTarget.index > location.index) {
-		normalizedIndex -= 1;
-	}
-
-	if (dropTarget.parentId === location.parentId && normalizedIndex === location.index) {
-		return [...nodes];
-	}
-
-	const removalResult = removeProjectTreeNode(nodes, draggedNodeId);
-
-	if (!removalResult.removed) {
-		return [...nodes];
-	}
-
-	return insertProjectTreeNode(removalResult.nodes, dropTarget.parentId, normalizedIndex, removalResult.removed);
+			: node,
 };
 
 const ProjectFolderDraftRow = (props: {
@@ -336,6 +174,7 @@ const ProjectFolderBranch = (props: {
 	onSubmitPendingFolder: () => void;
 	onCancelPendingFolder: () => void;
 	dragState: ProjectDragState | null;
+	isTreeClickSuppressed: () => boolean;
 }): JSX.Element => (
 	<ul class={styles.treeList} role="list">
 		<Show when={props.nodes.length === 0 && props.pendingFolderDraft?.parentId !== props.parentId}>
@@ -374,7 +213,7 @@ const ProjectFolderBranch = (props: {
 								style={{ "--tree-depth": String(props.depth) }}
 								aria-expanded={!isCollapsed()}
 								onClick={() => {
-									if (props.dragState || suppressNextTreeClick()) {
+									if (props.dragState || props.isTreeClickSuppressed()) {
 										return;
 									}
 
@@ -404,7 +243,7 @@ const ProjectFolderBranch = (props: {
 								</Show>
 							</button>
 
-							<Show when={!isCollapsed() && (node.children.length > 0 || props.pendingFolderDraft?.parentId === node.id)}>
+							<Show when={!isCollapsed() && ((node.children?.length ?? 0) > 0 || props.pendingFolderDraft?.parentId === node.id)}>
 								<ProjectFolderBranch
 									nodes={node.children}
 									depth={props.depth + 1}
@@ -423,6 +262,7 @@ const ProjectFolderBranch = (props: {
 									onSubmitPendingFolder={props.onSubmitPendingFolder}
 									onCancelPendingFolder={props.onCancelPendingFolder}
 									dragState={props.dragState}
+									isTreeClickSuppressed={props.isTreeClickSuppressed}
 								/>
 							</Show>
 						</li>
@@ -442,7 +282,7 @@ const ProjectFolderBranch = (props: {
 							}}
 							style={{ "--tree-depth": String(props.depth) }}
 							onClick={(): void => {
-								if (props.dragState || suppressNextTreeClick()) {
+								if (props.dragState || props.isTreeClickSuppressed()) {
 									return;
 								}
 
@@ -485,8 +325,9 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 	const [selectedProject, setSelectedProject] = createSignal(appShellData.activeProject());
 	const [drawerTop, setDrawerTop] = createSignal<number>(0);
 	const [collapsedFolderIds, setCollapsedFolderIds] = createSignal<readonly string[]>([]);
+	const [persistedFolders, setPersistedFolders] = createSignal<readonly PersistedProjectFolderRecord[]>([]);
 	const [projectTreeNodes, setProjectTreeNodes] = createSignal<ProjectTreeNode[]>(
-		buildProjectTree(appShellData.projectItems()),
+		buildProjectTree(appShellData.projectItems(), persistedFolders()),
 	);
 	const [pendingFolderDraft, setPendingFolderDraft] = createSignal<PendingProjectFolderDraft | null>(null);
 	const [pendingFolderName, setPendingFolderName] = createSignal("");
@@ -497,6 +338,8 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 	let contextMenuRef: HTMLDivElement | undefined;
 	let longPressTimer: number | undefined;
 	let suppressClickTimer: number | undefined;
+	let lastSelectedProjectId: string | null = null;
+	let latestPersistedFoldersRequest = 0;
 	const contextMenu = createProjectContextMenuController();
 
 	const clearLongPressTimer = (): void => {
@@ -527,16 +370,116 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 		);
 	};
 
+	const syncProjectTree = (): void => {
+		const nextTree = buildProjectTree(appShellData.projectItems(), persistedFolders());
+		const availableFolderIds = new Set(collectBranchNodeIds(nextTree, projectTreeAdapter));
+
+		setProjectTreeNodes(nextTree);
+		setCollapsedFolderIds((current) => current.filter((folderId) => availableFolderIds.has(folderId)));
+	};
+
+	const resetProjectTreeInteractionState = (): void => {
+		setCollapsedFolderIds([]);
+		setPendingFolderDraft(null);
+		setPendingFolderName("");
+		setDragState(null);
+	};
+
+	const folderIds = (): string[] => collectBranchNodeIds(projectTreeNodes(), projectTreeAdapter);
+
+	const expandAllFolders = (): void => {
+		setCollapsedFolderIds([]);
+	};
+
+	const collapseAllFolders = (): void => {
+		setCollapsedFolderIds(folderIds());
+	};
+
+	const totalFolderCount = (): number => folderIds().length;
+
+	const areAllFoldersCollapsed = (): boolean => {
+		const folderCount = totalFolderCount();
+
+		return folderCount > 0 && collapsedFolderIds().length >= folderCount;
+	};
+
+	const toggleAllFolders = (): void => {
+		if (areAllFoldersCollapsed()) {
+			expandAllFolders();
+			return;
+		}
+
+		collapseAllFolders();
+	};
+
+	const loadPersistedFolders = async (projectId: string): Promise<void> => {
+		const requestId = latestPersistedFoldersRequest + 1;
+		latestPersistedFoldersRequest = requestId;
+
+		if (!projectId) {
+			setPersistedFolders([]);
+			return;
+		}
+
+		if (!isUuidString(projectId)) {
+			setPersistedFolders([]);
+			return;
+		}
+
+		try {
+			const response = await fetch(`${resolveAPIBase()}/projects/${projectId}/folders`, {
+				headers: {
+					Accept: "application/json",
+				},
+			});
+			const body = (await response.json()) as ProjectFoldersResponse;
+
+			if (requestId !== latestPersistedFoldersRequest) {
+				return;
+			}
+
+			if (!response.ok) {
+				throw new Error(body.message || "Failed to load project folders.");
+			}
+
+			setPersistedFolders(readPersistedFolders(body));
+		} catch (error) {
+			if (requestId !== latestPersistedFoldersRequest) {
+				return;
+			}
+
+			console.error(error);
+			setPersistedFolders([]);
+		}
+	};
+
 	createEffect(() => {
 		setSelectedProject(appShellData.activeProject());
 	});
 
 	createEffect(() => {
-		setProjectTreeNodes(buildProjectTree(appShellData.projectItems()));
-		setCollapsedFolderIds([]);
-		setPendingFolderDraft(null);
-		setPendingFolderName("");
-		setDragState(null);
+		syncProjectTree();
+	});
+
+	createEffect(() => {
+		const projectId = selectedProject().id;
+
+		if (lastSelectedProjectId === null) {
+			lastSelectedProjectId = projectId;
+			return;
+		}
+
+		if (projectId === lastSelectedProjectId) {
+			return;
+		}
+
+		lastSelectedProjectId = projectId;
+		resetProjectTreeInteractionState();
+	});
+
+	createEffect(() => {
+		const projectId = selectedProject().id;
+		void loadPersistedFolders(projectId);
 	});
 
 	onMount(() => {
@@ -597,7 +540,7 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 
 			suppressTreeClickTemporarily();
 			setProjectTreeNodes((current) =>
-				moveProjectTreeNode(current, nextDragState.draggedNodeId, nextDragState.dropTarget as ProjectDragTarget),
+				moveTreeNode(current, nextDragState.draggedNodeId, nextDragState.dropTarget as ProjectDragTarget, projectTreeAdapter),
 			);
 			setDragState(null);
 		};
@@ -649,7 +592,7 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 	};
 
 	const selectProject = (projectId: string): void => {
-		const location = findProjectNodeLocation(projectTreeNodes(), projectId);
+		const location = findTreeNodeLocation(projectTreeNodes(), projectId, projectTreeAdapter);
 
 		if (!location || location.node.kind !== "project") {
 			return;
@@ -668,9 +611,10 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 		setPendingFolderDraft({ parentId, depth });
 	};
 
-	const submitPendingFolder = (): void => {
+	const submitPendingFolder = async (): Promise<void> => {
 		const name = pendingFolderName().trim();
 		const draft = pendingFolderDraft();
+		const projectId = selectedProject().id;
 
 		if (!draft) {
 			return;
@@ -682,16 +626,36 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 			return;
 		}
 
-		setProjectTreeNodes((current) =>
-			insertProjectFolderNode(current, draft.parentId, {
-				kind: "folder",
-				id: createProjectFolderId(),
-				label: name,
-				children: [],
-			}),
-		);
-		setPendingFolderDraft(null);
-		setPendingFolderName("");
+		if (!isUuidString(projectId)) {
+			cancelPendingFolder();
+			return;
+		}
+
+		try {
+			const response = await fetch(`${resolveAPIBase()}/projects/${projectId}/folders`, {
+				method: "POST",
+				headers: {
+					Accept: "application/json",
+					"Content-Type": "application/json",
+				},
+				body: JSON.stringify({
+					name,
+					parentFolderId: draft.parentId,
+				}),
+			});
+
+			const body = (await response.json()) as ProjectFoldersResponse;
+
+			if (!response.ok) {
+				throw new Error(body.message || "Failed to create project folder.");
+			}
+
+			setPersistedFolders(readPersistedFolders(body));
+			setPendingFolderDraft(null);
+			setPendingFolderName("");
+		} catch (error) {
+			console.error(error);
+		}
 	};
 
 	const cancelPendingFolder = (): void => {
@@ -704,16 +668,16 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 			return;
 		}
 
-		switch (target.kind) {
+			switch (target.kind) {
 			case "surface":
 				beginFolderDraft(null, 0);
 				return;
 			case "folder":
-				beginFolderDraft(target.id, (findProjectNodeDepth(projectTreeNodes(), target.id) ?? 0) + 1);
+				beginFolderDraft(target.id, (findTreeNodeDepth(projectTreeNodes(), target.id, projectTreeAdapter) ?? 0) + 1);
 				return;
 			case "project": {
-				const parentId = findProjectNodeLocation(projectTreeNodes(), target.id)?.parentId ?? null;
-				beginFolderDraft(parentId, parentId ? (findProjectNodeDepth(projectTreeNodes(), parentId) ?? 0) + 1 : 0);
+				const parentId = findTreeNodeLocation(projectTreeNodes(), target.id, projectTreeAdapter)?.parentId ?? null;
+				beginFolderDraft(parentId, parentId ? (findTreeNodeDepth(projectTreeNodes(), parentId, projectTreeAdapter) ?? 0) + 1 : 0);
 				return;
 			}
 		}
@@ -724,6 +688,9 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 		contextMenu.openMenu(event, createProjectSurfaceTarget("Projects"));
 	};
 
+	const treeControlLabel = (): string =>
+		areAllFoldersCollapsed() ? "Expand all folders" : "Collapse all folders";
+
 	const handleNodePointerDown = (event: PointerEvent, nodeId: string): void => {
 		if (event.button !== 0 || pendingFolderDraft()) {
 			return;
@@ -752,45 +719,20 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 			return;
 		}
 
-		const bounds = event.currentTarget.getBoundingClientRect();
-		const relativeY = bounds.height <= 0 ? 0.5 : (event.clientY - bounds.top) / bounds.height;
-		let nextTarget: ProjectDragTarget;
-
-		if (node.kind === "folder") {
-			if (relativeY < 0.28) {
-				nextTarget = {
-					parentId,
-					index,
-					intent: "before",
-					targetNodeId: node.id,
-				};
-			} else if (relativeY > 0.72) {
-				nextTarget = {
-					parentId,
-					index: index + 1,
-					intent: "after",
-					targetNodeId: node.id,
-				};
-			} else {
-				nextTarget = {
-					parentId: node.id,
-					index: node.children.length,
-					intent: "inside",
-					targetNodeId: node.id,
-				};
-			}
-		} else {
-			nextTarget = {
-				parentId,
-				index: relativeY < 0.5 ? index : index + 1,
-				intent: relativeY < 0.5 ? "before" : "after",
-				targetNodeId: node.item.id,
-			};
+		const relativeY = getPointerRelativeY(event);
+		if (relativeY === null) {
+			return;
 		}
 
 		setDragState({
 			...nextDragState,
-			dropTarget: nextTarget,
+			dropTarget: resolveTreeDropTarget({
+				parentId,
+				index,
+				node,
+				relativeY,
+				adapter: projectTreeAdapter,
+			}),
 		});
 	};
 
@@ -861,9 +803,29 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 						onContextMenu={handleSurfaceContextMenu}
 					>
 						<div class={styles.drawerBody}>
-							<Show when={!props.compact}>
-								<div class={styles.treeSectionLabel}>Projects</div>
-							</Show>
+							<div class={styles.treeSectionHeader}>
+								<Show when={!props.compact}>
+									<div class={styles.treeSectionLabel}>Projects</div>
+								</Show>
+
+								<div class={styles.treeControls}>
+									<button
+										type="button"
+										class={styles.treeControlButton}
+										onClick={toggleAllFolders}
+										aria-label={treeControlLabel()}
+										title={treeControlLabel()}
+										disabled={totalFolderCount() === 0}
+									>
+										<Show
+											when={areAllFoldersCollapsed()}
+											fallback={<ListCollapse size={16} strokeWidth={2} />}
+										>
+											<UnfoldVertical size={16} strokeWidth={2} />
+										</Show>
+									</button>
+								</div>
+							</div>
 
 							<ProjectFolderBranch
 								nodes={projectTreeNodes()}
@@ -889,6 +851,7 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 								onSubmitPendingFolder={submitPendingFolder}
 								onCancelPendingFolder={cancelPendingFolder}
 								dragState={dragState()}
+								isTreeClickSuppressed={suppressNextTreeClick}
 							/>
 						</div>
 					</div>

Frontend/src/components/shell/WorkspaceSidebar/WorkspaceSidebar.module.scss

@@ -1,3 +1,5 @@
+@use "../shared/tree-nav" as treeNav;
+
 .sidebar {
   --sidebar-nav-item-min-height: var(--control-size-lg);
   position: relative;
@@ -117,56 +119,25 @@
 }
 
 .treeSectionLabel {
-  @include text-caption;
+	@include treeNav.section-label;
   margin: var(--space-3) 0 var(--space-2);
   padding: 0 var(--space-3);
-  color: var(--color-text-subtle);
-  text-transform: uppercase;
-  letter-spacing: 0.04em;
 }
 
 .treeList {
-  list-style: none;
-  display: grid;
-  gap: var(--space-1);
-  padding: 0;
+	@include treeNav.tree-list;
 }
 
 .treeEmptySlot {
-	min-height: calc(var(--control-size-lg) - var(--space-2));
-	padding-left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
-	border-radius: var(--radius-lg);
-	border: 1px dashed color-mix(in srgb, var(--color-border) 38%, transparent);
-	opacity: 0.35;
+	@include treeNav.empty-slot;
 }
 
 .treeInputRow {
-	width: 100%;
-	min-width: 0;
-	display: grid;
-	grid-template-columns: auto minmax(0, 1fr);
-	align-items: center;
-	gap: var(--space-2);
-	min-height: calc(var(--control-size-lg) - var(--space-2));
-	padding: var(--space-2) var(--space-3);
-	padding-left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
-	border: 1px solid color-mix(in srgb, var(--color-border) 42%, transparent);
-	border-radius: var(--radius-lg);
-	background: color-mix(in srgb, var(--color-surface) 94%, transparent);
+	@include treeNav.input-row;
 }
 
 .treeInput {
-	width: 100%;
-	min-width: 0;
-	border: 0;
-	background: transparent;
-	color: var(--color-text);
-	font: inherit;
-	outline: none;
-}
-
-.treeInput::placeholder {
-	color: var(--color-text-muted);
+	@include treeNav.input;
 }
 
 .navItem {
@@ -184,74 +155,44 @@
 }
 
 .treeItem {
-  width: 100%;
-  min-width: 0;
-  display: grid;
-  grid-template-columns: auto auto minmax(0, 1fr) auto;
-  align-items: center;
-  gap: var(--space-2);
-  min-height: calc(var(--control-size-lg) - var(--space-2));
-  padding: var(--space-2) var(--space-3);
-  padding-left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
-  border: 1px solid transparent;
-  border-radius: var(--radius-lg);
-  background: transparent;
-  color: var(--color-text-muted);
-  text-align: left;
-  transition:
-    background 160ms var(--easing-standard),
-    color 160ms var(--easing-standard),
-    border-color 160ms var(--easing-standard),
-    box-shadow 160ms var(--easing-standard),
-    transform 180ms var(--easing-standard);
+	@include treeNav.item;
 }
 
 .treeItem:hover,
 .treeItem:focus-visible {
-  background: color-mix(in srgb, var(--color-surface-hover) 80%, var(--color-accent-soft) 20%);
-  color: var(--color-text);
-  box-shadow: inset 0 1px 0 color-mix(in srgb, white 4%, transparent);
+	@include treeNav.item-hover;
 }
 
 .treeItemFolder {
-  color: var(--color-text);
+	@include treeNav.item-folder;
 }
 
 .treeItemDragging {
-	opacity: 0.45;
-	transform: scale(0.985);
-	box-shadow: none;
+	@include treeNav.item-dragging;
 }
 
 .treeItemDropBefore {
-	box-shadow: inset 0 2px 0 color-mix(in srgb, var(--color-accent-strong) 78%, transparent);
+	@include treeNav.item-drop-before;
 }
 
 .treeItemDropAfter {
-	box-shadow: inset 0 -2px 0 color-mix(in srgb, var(--color-accent-strong) 78%, transparent);
+	@include treeNav.item-drop-after;
 }
 
 .treeItemDropInside {
-	border-color: color-mix(in srgb, var(--color-accent-strong) 55%, transparent);
-	background: color-mix(in srgb, var(--color-accent-soft) 36%, var(--color-surface));
-	color: var(--color-text);
-	box-shadow: inset 0 1px 0 color-mix(in srgb, white 4%, transparent);
+	@include treeNav.item-drop-inside;
 }
 
 .folderChevron {
-  color: var(--color-text-muted);
-  transition: transform 160ms var(--easing-standard);
+	@include treeNav.folder-chevron;
 }
 
 .folderChevronOpen {
-  transform: rotate(90deg);
+	@include treeNav.folder-chevron-open;
 }
 
 .treeItemActive {
-  border-color: var(--color-border);
-  background: var(--color-surface);
-  color: var(--color-text);
-  box-shadow: inset 0 1px 0 color-mix(in srgb, white 4%, transparent);
+	@include treeNav.item-active;
 }
 
 .navItemActive {
@@ -262,18 +203,15 @@
 }
 
 .icon {
-  color: inherit;
-  opacity: 0.85;
+	@include treeNav.icon;
 }
 
 .label {
-  @include text-label;
-  min-width: 0;
+	@include treeNav.label;
 }
 
 .itemMeta {
-  @include text-caption;
-  color: var(--color-text-muted);
+	@include treeNav.item-meta;
 }
 
 .sidebarCollapsed {

Frontend/src/components/shell/WorkspaceSidebar/WorkspaceSidebar.tsx

@@ -1,9 +1,20 @@
 // Path: Frontend/src/components/shell/WorkspaceSidebar/WorkspaceSidebar.tsx
 
 import { For, Show, createEffect, createSignal, onCleanup, onMount, type JSX } from "solid-js";
-import { ChevronLeft, ChevronRight, Folder } from "../../../lib/icons";
+import { resolveAPIBase } from "../../../lib/api";
+import { ChevronLeft, ChevronRight, Folder, ListCollapse, UnfoldVertical } from "../../../lib/icons";
 import { useAppShellData } from "../data/app-shell.context";
 import { ProjectSelector } from "../ProjectSelector/ProjectSelector";
+import {
+	collectBranchNodeIds,
+	findTreeNodeDepth,
+	getPointerRelativeY,
+	isUuidString,
+	moveTreeNode,
+	resolveTreeDropTarget,
+	type NavTreeAdapter,
+	type NavTreeDropTarget,
+} from "../shared/navTreeDnd";
 import {
 	createWorkspaceStaticTarget,
 	createWorkspaceSurfaceTarget,
@@ -31,217 +42,56 @@ type PendingWorkspaceFolderDraft = {
 	depth: number;
 };
 
-type WorkspaceDragTarget = {
-	parentId: string | null;
-	index: number;
-	intent: "before" | "after" | "inside";
-	targetNodeId?: string;
-};
+type WorkspaceDragTarget = NavTreeDropTarget;
 
 type WorkspaceDragState = {
 	draggedNodeId: string;
 	dropTarget: WorkspaceDragTarget | null;
 };
 
-type WorkspaceNodeLocation = {
-	parentId: string | null;
-	index: number;
-	node: WorkspaceTreeNode;
+type PersistedWorkspaceFolderRecord = {
+	id: string;
+	label: string;
+	children?: PersistedWorkspaceFolderRecord[];
+};
+
+type WorkspaceFoldersResponse = {
+	data?: {
+		folders?: PersistedWorkspaceFolderRecord[];
+	};
+	error?: string;
+	message?: string;
 };
 
 const LONG_PRESS_MS = 320;
 
-const createWorkspaceFolderId = (): string => `folder-${Math.random().toString(36).slice(2, 10)}`;
-
 const getWorkspaceTreeNodeId = (node: WorkspaceTreeNode): string => node.id;
 
-const insertWorkspaceFolderNode = (
-	nodes: readonly WorkspaceTreeNode[],
-	parentId: string | null,
-	folder: WorkspaceTreeNode,
-): readonly WorkspaceTreeNode[] => {
-	if (parentId === null) {
-		return [...nodes, folder];
-	}
+const buildPersistedWorkspaceFolderNodes = (
+	folders: readonly PersistedWorkspaceFolderRecord[],
+): WorkspaceTreeNode[] =>
+	folders.map((folder) => ({
+		id: folder.id,
+		label: folder.label,
+		kind: "folder",
+		icon: Folder,
+		children: buildPersistedWorkspaceFolderNodes(folder.children ?? []),
+	}));
 
-	return nodes.map((node) => {
-		if (node.kind !== "folder") {
-			return node;
-		}
+const readPersistedWorkspaceFolders = (body: WorkspaceFoldersResponse): PersistedWorkspaceFolderRecord[] =>
+	Array.isArray(body.data?.folders) ? body.data.folders : [];
 
-		if (node.id === parentId) {
-			return {
+const workspaceTreeAdapter: NavTreeAdapter<WorkspaceTreeNode> = {
+	getNodeId: getWorkspaceTreeNodeId,
+	isBranchNode: (node) => node.kind === "folder",
+	getChildren: (node) => (node.kind === "folder" ? (node.children ?? []) : []),
+	withChildren: (node, children) =>
+		node.kind === "folder"
+			? {
 				...node,
-				children: [...(node.children ?? []), folder],
-			};
-		}
-
-		return {
-			...node,
-			children: node.children ? insertWorkspaceFolderNode(node.children, parentId, folder) : node.children,
-		};
-	});
-};
-
-const findWorkspaceFolderDepth = (nodes: readonly WorkspaceTreeNode[], folderId: string, depth = 0): number | null => {
-	for (const node of nodes) {
-		if (node.kind !== "folder") {
-			continue;
-		}
-
-		if (node.id === folderId) {
-			return depth;
-		}
-
-		const nestedDepth = node.children ? findWorkspaceFolderDepth(node.children, folderId, depth + 1) : null;
-		if (nestedDepth !== null) {
-			return nestedDepth;
-		}
-	}
-
-	return null;
-};
-
-const findWorkspaceNodeLocation = (
-	nodes: readonly WorkspaceTreeNode[],
-	nodeId: string,
-	parentId: string | null = null,
-): WorkspaceNodeLocation | null => {
-	for (let index = 0; index < nodes.length; index += 1) {
-		const node = nodes[index];
-
-		if (node.id === nodeId) {
-			return { parentId, index, node };
-		}
-
-		if (node.kind === "folder" && node.children) {
-			const nestedLocation = findWorkspaceNodeLocation(node.children, nodeId, node.id);
-
-			if (nestedLocation) {
-				return nestedLocation;
+				children: [...children],
 			}
-		}
-	}
-
-	return null;
-};
-
-const workspaceTreeContainsNode = (nodes: readonly WorkspaceTreeNode[], nodeId: string): boolean => {
-	for (const node of nodes) {
-		if (node.id === nodeId) {
-			return true;
-		}
-
-		if (node.kind === "folder" && node.children && workspaceTreeContainsNode(node.children, nodeId)) {
-			return true;
-		}
-	}
-
-	return false;
-};
-
-const removeWorkspaceTreeNode = (
-	nodes: readonly WorkspaceTreeNode[],
-	nodeId: string,
-): { nodes: WorkspaceTreeNode[]; removed: WorkspaceTreeNode | null } => {
-	const nextNodes: WorkspaceTreeNode[] = [];
-	let removed: WorkspaceTreeNode | null = null;
-
-	for (const node of nodes) {
-		if (node.id === nodeId) {
-			removed = node;
-			continue;
-		}
-
-		if (node.kind === "folder" && node.children) {
-			const result = removeWorkspaceTreeNode(node.children, nodeId);
-
-			if (result.removed) {
-				removed = result.removed;
-				nextNodes.push({
-					...node,
-					children: result.nodes,
-				});
-				continue;
-			}
-		}
-
-		nextNodes.push(node);
-	}
-
-	return { nodes: nextNodes, removed };
-};
-
-const insertWorkspaceTreeNode = (
-	nodes: readonly WorkspaceTreeNode[],
-	parentId: string | null,
-	index: number,
-	nodeToInsert: WorkspaceTreeNode,
-): WorkspaceTreeNode[] => {
-	if (parentId === null) {
-		const nextNodes = [...nodes];
-		nextNodes.splice(Math.max(0, Math.min(index, nextNodes.length)), 0, nodeToInsert);
-		return nextNodes;
-	}
-
-	return nodes.map((node) => {
-		if (node.kind !== "folder") {
-			return node;
-		}
-
-		if (node.id === parentId) {
-			const nextChildren = [...(node.children ?? [])];
-			nextChildren.splice(Math.max(0, Math.min(index, nextChildren.length)), 0, nodeToInsert);
-			return {
-				...node,
-				children: nextChildren,
-			};
-		}
-
-		return {
-			...node,
-			children: node.children ? insertWorkspaceTreeNode(node.children, parentId, index, nodeToInsert) : node.children,
-		};
-	});
-};
-
-const moveWorkspaceTreeNode = (
-	nodes: readonly WorkspaceTreeNode[],
-	draggedNodeId: string,
-	dropTarget: WorkspaceDragTarget,
-): WorkspaceTreeNode[] => {
-	const location = findWorkspaceNodeLocation(nodes, draggedNodeId);
-
-	if (!location) {
-		return [...nodes];
-	}
-
-	if (
-		location.node.kind === "folder" &&
-		dropTarget.parentId !== null &&
-		((location.node.children && workspaceTreeContainsNode(location.node.children, dropTarget.parentId)) ||
-			dropTarget.parentId === location.node.id)
-	) {
-		return [...nodes];
-	}
-
-	let normalizedIndex = dropTarget.index;
-
-	if (dropTarget.parentId === location.parentId && dropTarget.index > location.index) {
-		normalizedIndex -= 1;
-	}
-
-	if (dropTarget.parentId === location.parentId && normalizedIndex === location.index) {
-		return [...nodes];
-	}
-
-	const removalResult = removeWorkspaceTreeNode(nodes, draggedNodeId);
-
-	if (!removalResult.removed) {
-		return [...nodes];
-	}
-
-	return insertWorkspaceTreeNode(removalResult.nodes, dropTarget.parentId, normalizedIndex, removalResult.removed);
+			: node,
 };
 
 const FolderDraftRow = (props: {
@@ -292,10 +142,6 @@ const WorkspaceHomeEntry = (props: {
 	item: WorkspaceStaticItem;
 	onOpenContextMenu: (event: MouseEvent, target: WorkspaceContextMenuTarget) => void;
 	onOpenContextMenuFromKeyboard: (element: HTMLElement, target: WorkspaceContextMenuTarget) => void;
-	onNodePointerDown: (event: PointerEvent, nodeId: string) => void;
-	onNodePointerMove: (event: PointerEvent, parentId: string | null, index: number, node: WorkspaceTreeNode) => void;
-	dragState: WorkspaceDragState | null;
-	isTreeClickSuppressed: () => boolean;
 }): JSX.Element => {
 	const Icon = props.item.icon;
 	const target = createWorkspaceStaticTarget(props.item);
@@ -350,17 +196,21 @@ const WorkspaceTreeBranch = (props: {
 	onCancelPendingFolder: () => void;
 	onOpenContextMenu: (event: MouseEvent, target: WorkspaceContextMenuTarget) => void;
 	onOpenContextMenuFromKeyboard: (element: HTMLElement, target: WorkspaceContextMenuTarget) => void;
+	onNodePointerDown: (event: PointerEvent, nodeId: string) => void;
+	onNodePointerMove: (event: PointerEvent, parentId: string | null, index: number, node: WorkspaceTreeNode) => void;
+	dragState: WorkspaceDragState | null;
+	isTreeClickSuppressed: () => boolean;
 }): JSX.Element => {
 	const depth = () => props.depth ?? 0;
 	const parentId = () => props.parentId ?? null;
 
 	return (
 		<ul class={styles.treeList} role="list">
-		<Show when={props.nodes.length === 0 && props.pendingFolderDraft?.parentId !== parentId()}>
-			<li>
-				<div class={styles.treeEmptySlot} style={{ "--tree-depth": String(depth()) }} />
-			</li>
-		</Show>
+			<Show when={props.nodes.length === 0 && props.pendingFolderDraft?.parentId !== parentId()}>
+				<li>
+					<div class={styles.treeEmptySlot} style={{ "--tree-depth": String(depth()) }} />
+				</li>
+			</Show>
 			<For each={props.nodes}>
 				{(node, indexAccessor): JSX.Element => {
 					const Icon = getWorkspaceNodeIcon(node);
@@ -485,24 +335,105 @@ const WorkspaceTreeBranch = (props: {
 
 export const WorkspaceSidebar = (props: WorkspaceSidebarProps): JSX.Element => {
 	const appShellData = useAppShellData();
+	const activeProject = () => appShellData.activeProject();
 	const [isProjectDrawerOpen, setIsProjectDrawerOpen] = createSignal(false);
 	const [workspaceTreeNodes, setWorkspaceTreeNodes] = createSignal<readonly WorkspaceTreeNode[]>(appShellData.workspaceTree());
+	const [persistedFolders, setPersistedFolders] = createSignal<readonly PersistedWorkspaceFolderRecord[]>([]);
 	const [collapsedFolderIds, setCollapsedFolderIds] = createSignal<readonly string[]>([]);
 	const [pendingFolderDraft, setPendingFolderDraft] = createSignal<PendingWorkspaceFolderDraft | null>(null);
 	const [pendingFolderName, setPendingFolderName] = createSignal("");
 	const [dragState, setDragState] = createSignal<WorkspaceDragState | null>(null);
 	const [suppressNextTreeClick, setSuppressNextTreeClick] = createSignal(false);
+	let lastSelectedProjectId: string | null = null;
+	let latestPersistedFoldersRequest = 0;
 	const contextMenu = createWorkspaceContextMenuController();
 	let longPressTimer: number | undefined;
 	let suppressClickTimer: number | undefined;
 	const railToggleLabel = (): string => (props.railCollapsed ? "Expand server rail" : "Collapse server rail");
 	const sidebarContextMenuTarget = createWorkspaceSurfaceTarget(appShellData.activeProject());
 	const isFolderCollapsed = (folderId: string): boolean => collapsedFolderIds().includes(folderId);
+	const folderIds = (): string[] => collectBranchNodeIds(workspaceTreeNodes(), workspaceTreeAdapter);
+	const totalFolderCount = (): number => folderIds().length;
+	const areAllFoldersCollapsed = (): boolean => {
+		const count = totalFolderCount();
+		return count > 0 && collapsedFolderIds().length >= count;
+	};
+	const workspaceFolderToggleLabel = (): string =>
+		areAllFoldersCollapsed() ? "Expand all folders" : "Collapse all folders";
 	const toggleFolder = (folderId: string): void => {
 		setCollapsedFolderIds((current) =>
 			current.includes(folderId) ? current.filter((id) => id !== folderId) : [...current, folderId],
 		);
 	};
+	const expandAllFolders = (): void => {
+		setCollapsedFolderIds([]);
+	};
+	const collapseAllFolders = (): void => {
+		setCollapsedFolderIds(folderIds());
+	};
+	const toggleAllFolders = (): void => {
+		if (areAllFoldersCollapsed()) {
+			expandAllFolders();
+			return;
+		}
+
+		collapseAllFolders();
+	};
+	const resetWorkspaceTreeInteractionState = (): void => {
+		setCollapsedFolderIds([]);
+		setPendingFolderDraft(null);
+		setPendingFolderName("");
+		setDragState(null);
+	};
+	const syncWorkspaceTree = (): void => {
+		const nextTree = activeProject()?.id
+			? buildPersistedWorkspaceFolderNodes(persistedFolders())
+			: appShellData.workspaceTree();
+		const availableFolderIds = new Set(collectBranchNodeIds(nextTree, workspaceTreeAdapter));
+
+		setWorkspaceTreeNodes(nextTree);
+		setCollapsedFolderIds((current) => current.filter((id) => availableFolderIds.has(id)));
+	};
+	const loadPersistedFolders = async (projectId: string): Promise<void> => {
+		const requestId = latestPersistedFoldersRequest + 1;
+		latestPersistedFoldersRequest = requestId;
+
+		if (!projectId) {
+			setPersistedFolders([]);
+			return;
+		}
+
+		if (!isUuidString(projectId)) {
+			setPersistedFolders([]);
+			return;
+		}
+
+		try {
+			const response = await fetch(`${resolveAPIBase()}/projects/${projectId}/tree/folders`, {
+				headers: {
+					Accept: "application/json",
+				},
+			});
+			const body = (await response.json()) as WorkspaceFoldersResponse;
+
+			if (requestId !== latestPersistedFoldersRequest) {
+				return;
+			}
+
+			if (!response.ok) {
+				throw new Error(body.message || "Failed to load project tree folders.");
+			}
+
+			setPersistedFolders(readPersistedWorkspaceFolders(body));
+		} catch (error) {
+			if (requestId !== latestPersistedFoldersRequest) {
+				return;
+			}
+
+			console.error(error);
+			setPersistedFolders([]);
+		}
+	};
 	const clearLongPressTimer = (): void => {
 		if (longPressTimer !== undefined) {
 			window.clearTimeout(longPressTimer);
@@ -523,11 +454,27 @@ export const WorkspaceSidebar = (props: WorkspaceSidebarProps): JSX.Element => {
 	};
 
 	createEffect(() => {
-		setWorkspaceTreeNodes(appShellData.workspaceTree());
-		setCollapsedFolderIds([]);
-		setPendingFolderDraft(null);
-		setPendingFolderName("");
-		setDragState(null);
+		syncWorkspaceTree();
+	});
+
+	createEffect(() => {
+		const projectId = activeProject()?.id ?? null;
+
+		if (lastSelectedProjectId === null) {
+			lastSelectedProjectId = projectId;
+			return;
+		}
+
+		if (projectId === lastSelectedProjectId) {
+			return;
+		}
+
+		lastSelectedProjectId = projectId;
+		resetWorkspaceTreeInteractionState();
+	});
+
+	createEffect(() => {
+		void loadPersistedFolders(activeProject()?.id ?? "");
 	});
 
 	onMount(() => {
@@ -546,7 +493,7 @@ export const WorkspaceSidebar = (props: WorkspaceSidebarProps): JSX.Element => {
 
 			suppressTreeClickTemporarily();
 			setWorkspaceTreeNodes((current) =>
-				moveWorkspaceTreeNode(current, nextDragState.draggedNodeId, nextDragState.dropTarget as WorkspaceDragTarget),
+				moveTreeNode(current, nextDragState.draggedNodeId, nextDragState.dropTarget as WorkspaceDragTarget, workspaceTreeAdapter),
 			);
 			setDragState(null);
 		};
@@ -587,9 +534,10 @@ export const WorkspaceSidebar = (props: WorkspaceSidebarProps): JSX.Element => {
 		setPendingFolderDraft({ parentId, depth });
 	};
 
-	const submitPendingFolder = (): void => {
+	const submitPendingFolder = async (): Promise<void> => {
 		const name = pendingFolderName().trim();
 		const draft = pendingFolderDraft();
+		const projectId = activeProject()?.id ?? "";
 
 		if (!draft) {
 			return;
@@ -601,17 +549,36 @@ export const WorkspaceSidebar = (props: WorkspaceSidebarProps): JSX.Element => {
 			return;
 		}
 
-		setWorkspaceTreeNodes((current) =>
-			insertWorkspaceFolderNode(current, draft.parentId, {
-				id: createWorkspaceFolderId(),
-				label: name,
-				kind: "folder",
-				icon: Folder,
-				children: [],
-			}),
-		);
-		setPendingFolderDraft(null);
-		setPendingFolderName("");
+		if (!projectId || !isUuidString(projectId)) {
+			cancelPendingFolder();
+			return;
+		}
+
+		try {
+			const response = await fetch(`${resolveAPIBase()}/projects/${projectId}/tree/folders`, {
+				method: "POST",
+				headers: {
+					Accept: "application/json",
+					"Content-Type": "application/json",
+				},
+				body: JSON.stringify({
+					name,
+					parentFolderId: draft.parentId,
+				}),
+			});
+
+			const body = (await response.json()) as WorkspaceFoldersResponse;
+
+			if (!response.ok) {
+				throw new Error(body.message || "Failed to create project tree folder.");
+			}
+
+			setPersistedFolders(readPersistedWorkspaceFolders(body));
+			setPendingFolderDraft(null);
+			setPendingFolderName("");
+		} catch (error) {
+			console.error(error);
+		}
 	};
 
 	const cancelPendingFolder = (): void => {
@@ -619,6 +586,17 @@ export const WorkspaceSidebar = (props: WorkspaceSidebarProps): JSX.Element => {
 		setPendingFolderName("");
 	};
 
+	const handleHeaderActionClick = (actionId: string): void => {
+		switch (actionId) {
+			case "toggle-workspace-folders":
+				toggleAllFolders();
+				return;
+			case "search-workspace":
+			default:
+				return;
+		}
+	};
+
 	const handleNodePointerDown = (event: PointerEvent, nodeId: string): void => {
 		if (event.button !== 0 || pendingFolderDraft()) {
 			return;
@@ -643,33 +621,21 @@ export const WorkspaceSidebar = (props: WorkspaceSidebarProps): JSX.Element => {
 			return;
 		}
 
-		const bounds = event.currentTarget.getBoundingClientRect();
-		const relativeY = bounds.height <= 0 ? 0.5 : (event.clientY - bounds.top) / bounds.height;
-		let nextTarget: WorkspaceDragTarget;
-
-		if (node.kind === "folder") {
-			if (relativeY < 0.28) {
-				nextTarget = { parentId, index, intent: "before", targetNodeId: node.id };
-			} else if (relativeY > 0.72) {
-				nextTarget = { parentId, index: index + 1, intent: "after", targetNodeId: node.id };
-			} else {
-				nextTarget = {
-					parentId: node.id,
-					index: (node.children ?? []).length,
-					intent: "inside",
-					targetNodeId: node.id,
-				};
-			}
-		} else {
-			nextTarget = {
-				parentId,
-				index: relativeY < 0.5 ? index : index + 1,
-				intent: relativeY < 0.5 ? "before" : "after",
-				targetNodeId: node.id,
-			};
+		const relativeY = getPointerRelativeY(event);
+		if (relativeY === null) {
+			return;
 		}
 
-		setDragState({ ...nextDragState, dropTarget: nextTarget });
+		setDragState({
+			...nextDragState,
+			dropTarget: resolveTreeDropTarget({
+				parentId,
+				index,
+				node,
+				relativeY,
+				adapter: workspaceTreeAdapter,
+			}),
+		});
 	};
 
 	const handleContextActionSelect = (action: WorkspaceContextMenuAction, target: WorkspaceContextMenuTarget): void => {
@@ -677,13 +643,13 @@ export const WorkspaceSidebar = (props: WorkspaceSidebarProps): JSX.Element => {
 			return;
 		}
 
-		switch (target.kind) {
+			switch (target.kind) {
 			case "workspace":
 			case "home":
 				beginFolderDraft(null, 0);
 				return;
 			case "folder":
-				beginFolderDraft(target.id, (findWorkspaceFolderDepth(workspaceTreeNodes(), target.id) ?? 0) + 1);
+				beginFolderDraft(target.id, (findTreeNodeDepth(workspaceTreeNodes(), target.id, workspaceTreeAdapter) ?? 0) + 1);
 				return;
 			case "settings":
 			case "item":
@@ -729,12 +695,30 @@ export const WorkspaceSidebar = (props: WorkspaceSidebarProps): JSX.Element => {
 							{props.railCollapsed ? <ChevronRight size={16} strokeWidth={2} /> : <ChevronLeft size={16} strokeWidth={2} />}
 						</button>
 
-						<For each={workspaceSidebarHeaderActions}>
-							{(action): JSX.Element => {
-								const Icon = action.icon;
+					<For each={workspaceSidebarHeaderActions}>
+						{(action): JSX.Element => {
+							const label =
+								action.id === "toggle-workspace-folders"
+										? workspaceFolderToggleLabel()
+										: action.label;
+							const Icon =
+								action.id === "toggle-workspace-folders"
+										? areAllFoldersCollapsed()
+											? UnfoldVertical
+											: ListCollapse
+										: action.icon;
 
-								return (
-									<button type="button" class={styles.headerActionButton} aria-label={action.label} title={action.label} data-slot="workspace-sidebar-header-action" data-action-id={action.id}>
+							return (
+								<button
+									type="button"
+									class={styles.headerActionButton}
+									aria-label={label}
+									title={label}
+									data-slot="workspace-sidebar-header-action"
+									data-action-id={action.id}
+									disabled={action.id === "toggle-workspace-folders" && totalFolderCount() === 0}
+									onClick={(): void => handleHeaderActionClick(action.id)}
+									>
 										<Icon size={16} strokeWidth={2} />
 									</button>
 								);
@@ -794,13 +778,13 @@ export const WorkspaceSidebar = (props: WorkspaceSidebarProps): JSX.Element => {
 								onPendingFolderNameChange={setPendingFolderName}
 								onSubmitPendingFolder={submitPendingFolder}
 								onCancelPendingFolder={cancelPendingFolder}
-								onOpenContextMenu={contextMenu.openMenu}
-								onOpenContextMenuFromKeyboard={contextMenu.openMenuFromElement}
-								onNodePointerDown={handleNodePointerDown}
-								onNodePointerMove={handleNodePointerMove}
-								dragState={dragState()}
-								isTreeClickSuppressed={suppressNextTreeClick}
-							/>
+									onOpenContextMenu={contextMenu.openMenu}
+									onOpenContextMenuFromKeyboard={contextMenu.openMenuFromElement}
+									onNodePointerDown={handleNodePointerDown}
+									onNodePointerMove={handleNodePointerMove}
+									dragState={dragState()}
+									isTreeClickSuppressed={suppressNextTreeClick}
+								/>
 						</div>
 					</div>
 				</div>

Frontend/src/components/shell/data/shell.data.ts

@@ -9,6 +9,7 @@ import {
 	Home,
 	Keyboard,
 	LayoutGrid,
+	ListCollapse,
 	LogOut,
 	Repeat,
 	Search,
@@ -476,6 +477,7 @@ export const workspaceTree: readonly WorkspaceTreeNode[] = [
 
 export const workspaceSidebarHeaderActions: readonly SidebarHeaderAction[] = [
 	{ id: "search-workspace", label: "Search workspace", icon: Search },
+	{ id: "toggle-workspace-folders", label: "Collapse all folders", icon: ListCollapse },
 ] as const;
 
 export const mobileBottomNavItems: readonly MobileBottomNavItem[] = [

Frontend/src/components/shell/shared/_tree-nav.scss

@@ -0,0 +1,188 @@
+@use "../../../styles/tools/mixins" as *;
+
+@mixin section-label {
+	@include text-caption;
+	color: var(--color-text-subtle);
+	text-transform: uppercase;
+	letter-spacing: 0.04em;
+}
+
+@mixin tree-list {
+	list-style: none;
+	display: grid;
+	gap: var(--space-1);
+	padding: 0;
+}
+
+@mixin empty-slot {
+	min-height: calc(var(--control-size-lg) - var(--space-2));
+	padding-left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
+	border-radius: var(--radius-lg);
+	border: 1px dashed color-mix(in srgb, var(--color-border) 38%, transparent);
+	opacity: 0.35;
+}
+
+@mixin input-row {
+	width: 100%;
+	min-width: 0;
+	display: grid;
+	grid-template-columns: auto minmax(0, 1fr);
+	align-items: center;
+	gap: var(--space-2);
+	min-height: calc(var(--control-size-lg) - var(--space-2));
+	padding: var(--space-2) var(--space-3);
+	padding-left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
+	border: 1px solid color-mix(in srgb, var(--color-border) 42%, transparent);
+	border-radius: var(--radius-lg);
+	background: color-mix(in srgb, var(--color-surface) 94%, transparent);
+}
+
+@mixin input {
+	width: 100%;
+	min-width: 0;
+	border: 0;
+	background: transparent;
+	color: var(--color-text);
+	font: inherit;
+	outline: none;
+
+	&::placeholder {
+		color: var(--color-text-muted);
+	}
+}
+
+@mixin item {
+	width: 100%;
+	min-width: 0;
+	display: grid;
+	position: relative;
+	isolation: isolate;
+	grid-template-columns: auto auto minmax(0, 1fr) auto;
+	align-items: center;
+	gap: var(--space-2);
+	min-height: calc(var(--control-size-lg) - var(--space-2));
+	padding: var(--space-2) var(--space-3);
+	padding-left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
+	border: 0;
+	border-radius: 0;
+	background: transparent;
+	color: var(--color-text-muted);
+	text-align: left;
+	transition:
+		color 160ms var(--easing-standard),
+		box-shadow 160ms var(--easing-standard),
+		transform 180ms var(--easing-standard);
+
+	&::after {
+		content: "";
+		position: absolute;
+		inset: 0;
+		border: 1px solid transparent;
+		border-radius: var(--radius-lg);
+		background: transparent;
+		transition:
+			background 160ms var(--easing-standard),
+			border-color 160ms var(--easing-standard),
+			box-shadow 160ms var(--easing-standard);
+		pointer-events: none;
+		z-index: 0;
+	}
+
+	> * {
+		position: relative;
+		z-index: 1;
+	}
+}
+
+@mixin item-hover {
+	color: var(--color-text);
+
+	&::after {
+		background: color-mix(in srgb, var(--color-surface-hover) 80%, var(--color-accent-soft) 20%);
+		box-shadow: inset 0 1px 0 color-mix(in srgb, white 4%, transparent);
+	}
+}
+
+@mixin item-folder {
+	color: var(--color-text);
+}
+
+@mixin item-dragging {
+	opacity: 0.45;
+	transform: scale(0.985);
+	box-shadow: none;
+}
+
+@mixin item-drop-before {
+	&::before {
+		content: "";
+		position: absolute;
+		left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
+		right: var(--space-3);
+		top: calc((var(--space-1) * -0.5) - 1px);
+		height: 2px;
+		border-radius: 999px;
+		background: color-mix(in srgb, var(--color-accent-strong) 78%, transparent);
+		pointer-events: none;
+		z-index: 2;
+	}
+}
+
+@mixin item-drop-after {
+	&::before {
+		content: "";
+		position: absolute;
+		left: calc(var(--space-3) + (var(--tree-depth, 0) * var(--space-4)));
+		right: var(--space-3);
+		bottom: calc((var(--space-1) * -0.5) - 1px);
+		height: 2px;
+		border-radius: 999px;
+		background: color-mix(in srgb, var(--color-accent-strong) 78%, transparent);
+		pointer-events: none;
+		z-index: 2;
+	}
+}
+
+@mixin item-drop-inside {
+	color: var(--color-text);
+
+	&::after {
+		border-color: color-mix(in srgb, var(--color-accent-strong) 55%, transparent);
+		background: color-mix(in srgb, var(--color-accent-soft) 36%, var(--color-surface));
+		box-shadow: inset 0 1px 0 color-mix(in srgb, white 4%, transparent);
+	}
+}
+
+@mixin folder-chevron {
+	color: var(--color-text-muted);
+	transition: transform 160ms var(--easing-standard);
+}
+
+@mixin folder-chevron-open {
+	transform: rotate(90deg);
+}
+
+@mixin item-active {
+	color: var(--color-text);
+
+	&::after {
+		border-color: var(--color-border);
+		background: var(--color-surface);
+		box-shadow: inset 0 1px 0 color-mix(in srgb, white 4%, transparent);
+	}
+}
+
+@mixin icon {
+	color: inherit;
+	opacity: 0.85;
+}
+
+@mixin label {
+	@include text-label;
+	min-width: 0;
+}
+
+@mixin item-meta {
+	@include text-caption;
+	color: var(--color-text-muted);
+}

Frontend/src/components/shell/shared/navTreeDnd.ts

@@ -0,0 +1,278 @@
+export type NavTreeDropIntent = "before" | "after" | "inside";
+
+export type NavTreeDropTarget = {
+	parentId: string | null;
+	index: number;
+	intent: NavTreeDropIntent;
+	targetNodeId?: string;
+};
+
+export type NavTreeDragState = {
+	draggedNodeId: string;
+	dropTarget: NavTreeDropTarget | null;
+};
+
+export type NavTreeLocation<TNode> = {
+	parentId: string | null;
+	index: number;
+	node: TNode;
+};
+
+export type NavTreeAdapter<TNode> = {
+	getNodeId: (node: TNode) => string;
+	isBranchNode: (node: TNode) => boolean;
+	getChildren: (node: TNode) => readonly TNode[];
+	withChildren: (node: TNode, children: readonly TNode[]) => TNode;
+};
+
+const UUID_PATTERN = /^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;
+
+export const isUuidString = (value: string | null | undefined): boolean => {
+	if (typeof value !== "string") {
+		return false;
+	}
+
+	return UUID_PATTERN.test(value.trim());
+};
+
+export const collectBranchNodeIds = <TNode>(
+	nodes: readonly TNode[],
+	adapter: NavTreeAdapter<TNode>,
+): string[] => {
+	const ids: string[] = [];
+
+	for (const node of nodes) {
+		if (!adapter.isBranchNode(node)) {
+			continue;
+		}
+
+		ids.push(adapter.getNodeId(node));
+		ids.push(...collectBranchNodeIds(adapter.getChildren(node), adapter));
+	}
+
+	return ids;
+};
+
+export const findTreeNodeLocation = <TNode>(
+	nodes: readonly TNode[],
+	nodeId: string,
+	adapter: NavTreeAdapter<TNode>,
+	parentId: string | null = null,
+): NavTreeLocation<TNode> | null => {
+	for (let index = 0; index < nodes.length; index += 1) {
+		const node = nodes[index];
+
+		if (adapter.getNodeId(node) === nodeId) {
+			return { parentId, index, node };
+		}
+
+		if (!adapter.isBranchNode(node)) {
+			continue;
+		}
+
+		const nestedLocation = findTreeNodeLocation(adapter.getChildren(node), nodeId, adapter, adapter.getNodeId(node));
+		if (nestedLocation) {
+			return nestedLocation;
+		}
+	}
+
+	return null;
+};
+
+export const findTreeNodeDepth = <TNode>(
+	nodes: readonly TNode[],
+	nodeId: string,
+	adapter: NavTreeAdapter<TNode>,
+	depth = 0,
+): number | null => {
+	for (const node of nodes) {
+		if (adapter.getNodeId(node) === nodeId) {
+			return depth;
+		}
+
+		if (!adapter.isBranchNode(node)) {
+			continue;
+		}
+
+		const nestedDepth = findTreeNodeDepth(adapter.getChildren(node), nodeId, adapter, depth + 1);
+		if (nestedDepth !== null) {
+			return nestedDepth;
+		}
+	}
+
+	return null;
+};
+
+export const treeContainsNode = <TNode>(
+	nodes: readonly TNode[],
+	nodeId: string,
+	adapter: NavTreeAdapter<TNode>,
+): boolean => {
+	for (const node of nodes) {
+		if (adapter.getNodeId(node) === nodeId) {
+			return true;
+		}
+
+		if (adapter.isBranchNode(node) && treeContainsNode(adapter.getChildren(node), nodeId, adapter)) {
+			return true;
+		}
+	}
+
+	return false;
+};
+
+export const removeTreeNode = <TNode>(
+	nodes: readonly TNode[],
+	nodeId: string,
+	adapter: NavTreeAdapter<TNode>,
+): { nodes: TNode[]; removed: TNode | null } => {
+	const nextNodes: TNode[] = [];
+	let removed: TNode | null = null;
+
+	for (const node of nodes) {
+		if (adapter.getNodeId(node) === nodeId) {
+			removed = node;
+			continue;
+		}
+
+		if (adapter.isBranchNode(node)) {
+			const result = removeTreeNode(adapter.getChildren(node), nodeId, adapter);
+
+			if (result.removed) {
+				removed = result.removed;
+				nextNodes.push(adapter.withChildren(node, result.nodes));
+				continue;
+			}
+		}
+
+		nextNodes.push(node);
+	}
+
+	return { nodes: nextNodes, removed };
+};
+
+export const insertTreeNode = <TNode>(
+	nodes: readonly TNode[],
+	parentId: string | null,
+	index: number,
+	nodeToInsert: TNode,
+	adapter: NavTreeAdapter<TNode>,
+): TNode[] => {
+	if (parentId === null) {
+		const nextNodes = [...nodes];
+		nextNodes.splice(Math.max(0, Math.min(index, nextNodes.length)), 0, nodeToInsert);
+		return nextNodes;
+	}
+
+	return nodes.map((node) => {
+		if (!adapter.isBranchNode(node)) {
+			return node;
+		}
+
+		if (adapter.getNodeId(node) === parentId) {
+			const nextChildren = [...adapter.getChildren(node)];
+			nextChildren.splice(Math.max(0, Math.min(index, nextChildren.length)), 0, nodeToInsert);
+			return adapter.withChildren(node, nextChildren);
+		}
+
+		return adapter.withChildren(node, insertTreeNode(adapter.getChildren(node), parentId, index, nodeToInsert, adapter));
+	});
+};
+
+export const moveTreeNode = <TNode>(
+	nodes: readonly TNode[],
+	draggedNodeId: string,
+	dropTarget: NavTreeDropTarget,
+	adapter: NavTreeAdapter<TNode>,
+): TNode[] => {
+	const location = findTreeNodeLocation(nodes, draggedNodeId, adapter);
+
+	if (!location) {
+		return [...nodes];
+	}
+
+	if (
+		adapter.isBranchNode(location.node) &&
+		dropTarget.parentId !== null &&
+		(treeContainsNode(adapter.getChildren(location.node), dropTarget.parentId, adapter) ||
+			dropTarget.parentId === adapter.getNodeId(location.node))
+	) {
+		return [...nodes];
+	}
+
+	let normalizedIndex = dropTarget.index;
+	if (dropTarget.parentId === location.parentId && dropTarget.index > location.index) {
+		normalizedIndex -= 1;
+	}
+
+	if (dropTarget.parentId === location.parentId && normalizedIndex === location.index) {
+		return [...nodes];
+	}
+
+	const removalResult = removeTreeNode(nodes, draggedNodeId, adapter);
+	if (!removalResult.removed) {
+		return [...nodes];
+	}
+
+	return insertTreeNode(removalResult.nodes, dropTarget.parentId, normalizedIndex, removalResult.removed, adapter);
+};
+
+export const getPointerRelativeY = (event: PointerEvent): number | null => {
+	const currentTarget = event.currentTarget;
+	if (!(currentTarget instanceof HTMLElement)) {
+		return null;
+	}
+
+	const bounds = currentTarget.getBoundingClientRect();
+	return bounds.height <= 0 ? 0.5 : (event.clientY - bounds.top) / bounds.height;
+};
+
+export const resolveTreeDropTarget = <TNode>(params: {
+	parentId: string | null;
+	index: number;
+	node: TNode;
+	relativeY: number;
+	adapter: NavTreeAdapter<TNode>;
+	beforeThreshold?: number;
+	beforeThresholdFirstSibling?: number;
+	afterThreshold?: number;
+}): NavTreeDropTarget => {
+	const {
+		parentId,
+		index,
+		node,
+		relativeY,
+		adapter,
+		beforeThreshold = 0.28,
+		beforeThresholdFirstSibling = 0.42,
+		afterThreshold = 0.72,
+	} = params;
+
+	const targetNodeId = adapter.getNodeId(node);
+
+	if (adapter.isBranchNode(node)) {
+		const nextBeforeThreshold = index === 0 ? beforeThresholdFirstSibling : beforeThreshold;
+
+		if (relativeY < nextBeforeThreshold) {
+			return { parentId, index, intent: "before", targetNodeId };
+		}
+
+		if (relativeY > afterThreshold) {
+			return { parentId, index: index + 1, intent: "after", targetNodeId };
+		}
+
+		return {
+			parentId: targetNodeId,
+			index: adapter.getChildren(node).length,
+			intent: "inside",
+			targetNodeId,
+		};
+	}
+
+	return {
+		parentId,
+		index: relativeY < 0.5 ? index : index + 1,
+		intent: relativeY < 0.5 ? "before" : "after",
+		targetNodeId,
+	};
+};

Frontend/src/lib/icons/index.ts

@@ -10,6 +10,7 @@ export { default as Folder } from "lucide-solid/icons/folder";
 export { default as Home } from "lucide-solid/icons/house";
 export { default as Keyboard } from "lucide-solid/icons/keyboard";
 export { default as LayoutGrid } from "lucide-solid/icons/layout-grid";
+export { default as ListCollapse } from "lucide-solid/icons/list-collapse";
 export { default as LogOut } from "lucide-solid/icons/log-out";
 export { default as Moon } from "lucide-solid/icons/moon";
 export { default as Plus } from "lucide-solid/icons/plus";
@@ -18,5 +19,6 @@ export { default as Search } from "lucide-solid/icons/search";
 export { default as Settings } from "lucide-solid/icons/settings";
 export { default as Shield } from "lucide-solid/icons/shield";
 export { default as Sun } from "lucide-solid/icons/sun";
+export { default as UnfoldVertical } from "lucide-solid/icons/unfold-vertical";
 export { default as User } from "lucide-solid/icons/user";
 export { default as X } from "lucide-solid/icons/x";