feat(breadcrumb): build breadcrumb in 1 API call

add /api/folders/{id}/ancestors

    this API to iterate parent up to the drive root or the shared folder
    this will help UI to build the breadcrumb in 1 API call
    and to identify the root element (is it a drive users has access to or
    a shared folder ?)

    ui: now only 1 API call is now required to build the breadcrumb

src/interfaces/api/handlers/folder_handler.rs

@@ -12,8 +12,8 @@ use crate::application::dtos::display_helpers::{
 };
 use crate::application::dtos::file_dto::FileDto;
 use crate::application::dtos::folder_dto::{
-    CreateFolderDto, FolderDto, FolderResourceItemDto, FolderResourcesDto, FolderResourcesQuery,
-    ListResourcesOptions, MoveFolderDto, RenameFolderDto,
+    CreateFolderDto, FolderAncestorsDto, FolderDto, FolderResourceItemDto, FolderResourcesDto,
+    FolderResourcesQuery, ListResourcesOptions, MoveFolderDto, RenameFolderDto,
 };
 use crate::application::dtos::grant_dto::{ResourceContentDto, ResourceTypeDto};
 use crate::application::ports::external_mount_ports::MountEntry;
@@ -112,6 +112,21 @@ impl FolderHandler {
         }
     }
 
+    /// `GET /api/folders/{id}/ancestors` — parent-chain + access-source
+    /// for the shared breadcrumb component. See `FolderAncestorsDto`
+    /// for the response shape. Anti-enum via `NotFound` on Read denial.
+    pub(super) async fn get_folder_ancestors_impl(
+        State(state): State<Arc<GlobalAppState>>,
+        auth_user: AuthUser,
+        Path(id): Path<String>,
+    ) -> impl IntoResponse {
+        let service = &state.applications.folder_service_concrete;
+        match service.get_ancestors_with_perms(&id, auth_user.id).await {
+            Ok(dto) => (StatusCode::OK, Json(dto)).into_response(),
+            Err(err) => AppError::from(err).into_response(),
+        }
+    }
+
     /// Lists root folders for the authenticated user.
     /// Only returns folders owned by this user — no information disclosure.
     pub(super) async fn list_root_folders_impl(
@@ -367,6 +382,25 @@ pub async fn get_folder(
     FolderHandler::get_folder_impl(state, auth_user, path).await
 }
 
+#[utoipa::path(
+    get,
+    path = "/api/folders/{id}/ancestors",
+    params(("id" = String, Path, description = "Leaf folder ID — the walk starts here and climbs the parent chain up to the drive root or the caller's share/drive-membership boundary.")),
+    responses(
+        (status = 200, description = "Ancestor chain + access-source. `ancestors` is root-first, leaf-last (length ≥ 1). See `FolderAncestorsDto`.", body = FolderAncestorsDto),
+        (status = 404, description = "Folder not found or caller lacks Read (anti-enum)"),
+    ),
+    security(("bearerAuth" = [])),
+    tag = "folders"
+)]
+pub async fn get_folder_ancestors(
+    state: State<Arc<GlobalAppState>>,
+    auth_user: AuthUser,
+    path: Path<String>,
+) -> impl IntoResponse {
+    FolderHandler::get_folder_ancestors_impl(state, auth_user, path).await
+}
+
 #[utoipa::path(
     get,
     path = "/api/folders",

src/interfaces/api/mod.rs

@@ -20,7 +20,9 @@ use crate::application::dtos::favorites_dto::{
 };
 use crate::application::dtos::file_dto::FileDto;
 use crate::application::dtos::folder_dto::{
-    CreateFolderDto, FolderDto, FolderResourceItemDto, MoveFolderDto, RenameFolderDto,
+    AccessSourceDriveDto, AccessSourceDto, AccessSourceKind, AccessSourceSubjectDto,
+    AccessSourceSubjectKind, CreateFolderDto, FolderAncestorDto, FolderAncestorsDto, FolderDto,
+    FolderResourceItemDto, MoveFolderDto, RenameFolderDto,
 };
 use crate::application::dtos::folder_listing_dto::FolderListingDto;
 use crate::application::dtos::grant_dto::{
@@ -96,6 +98,7 @@ use crate::interfaces::api::handlers::file_handler::MoveFilePayload;
         // Folder handlers (free functions — see folder_handler.rs for why)
         handlers::folder_handler::create_folder,
         handlers::folder_handler::get_folder,
+        handlers::folder_handler::get_folder_ancestors,
         handlers::folder_handler::list_root_folders,
         handlers::folder_handler::list_folder_resources,
         handlers::folder_handler::rename_folder,
@@ -264,6 +267,14 @@ use crate::interfaces::api::handlers::file_handler::MoveFilePayload;
             FolderListingDto,
             FolderResourceItemDto,
             ResourceContentDto,
+            // Folder ancestor chain (breadcrumb endpoint)
+            FolderAncestorsDto,
+            FolderAncestorDto,
+            AccessSourceDto,
+            AccessSourceKind,
+            AccessSourceDriveDto,
+            AccessSourceSubjectDto,
+            AccessSourceSubjectKind,
             // File schemas
             FileDto,
             // Delta-upload schemas

src/interfaces/api/routes.rs

@@ -82,7 +82,7 @@ use crate::interfaces::api::handlers::file_handler::{
     list_files_query, move_file_simple, rename_file, upload_file_with_thumbnails, upload_thumbnail,
 };
 use crate::interfaces::api::handlers::folder_handler::{
-    create_folder, delete_folder_with_trash, download_folder_zip, get_folder,
+    create_folder, delete_folder_with_trash, download_folder_zip, get_folder, get_folder_ancestors,
     list_folder_resources, list_root_folders, move_folder, rename_folder,
 };
 use crate::interfaces::api::handlers::i18n_handler::{
@@ -218,6 +218,11 @@ pub fn create_api_routes(app_state: &Arc<AppState>) -> Router<Arc<AppState>> {
     let folders_crud_router = Router::new()
         .route("/", post(create_folder))
         .route("/{id}", get(get_folder))
+        // Ancestor chain for the shared breadcrumb component — one
+        // round-trip vs the pre-2026-07-26 per-segment `getFolder` walk
+        // on the /files client. Returns caller-visible parents (walk
+        // stops at share/drive-membership boundary) + access_source.
+        .route("/{id}/ancestors", get(get_folder_ancestors))
         .route("/{id}/rename", put(rename_folder))
         .route("/{id}/move", put(move_folder))
         .with_state(app_state.clone());