feat(file): conceal file resource existence from other users

- feat: cross-user file access returns not-found instead of
  permission-denied
- fix: repository delete now only affects active rows and returns
  ErrNotFound when no row changes; repeated deletes yield not-found
- feat: parent directory operations (list, upload, create-dir, move)
  conceal ownership of other user's directories
- test: update handler, service, repository, and integration tests to
  assert not-found behavior for cross-user and missing file operations

docs/server/decisions.md

@@ -106,3 +106,20 @@
 - REST remains a handler/API concern, and future protocols can reuse services without HTTP leakage.
 - Error responses keep the same top-level shape, with optional `log_id` instead of embedding log references in the message.
 - Admin and auth middleware behavior is testable through service contracts rather than database access.
+
+## 2026-07-15: Conceal File Resource Existence
+
+**Context**: Returning permission-denied errors for cross-user file access allowed authenticated callers to distinguish another user's resource from a missing resource. Idempotent success for deleting missing files also conflicted with a consistent not-found concealment policy.
+
+**Decisions**:
+
+| Decision | Guidance |
+|----------|----------|
+| Conceal ownership | File and parent-directory ownership failures return the same not-found kind and safe message as missing or deleted resources. |
+| Strict delete result | Deleting an active owned file returns success once; missing, deleted, and cross-user targets return not found. |
+| Atomic soft delete | Repository deletes update only active rows and return `model.ErrNotFound` when no row changes. |
+
+**Consequences**:
+- Authenticated file operations cannot use status codes or messages to determine whether another user's resource exists.
+- A successful first delete returns `204 No Content`; repeated deletes return `404 Not Found` while remaining idempotent in effect.
+- Unauthenticated requests remain `401 Unauthorized`, non-empty directory deletion remains `409 Conflict`, and permission-denied behavior outside the file boundary remains unchanged.

docs/server/roadmap.md

@@ -27,7 +27,7 @@ Package-level implementation order (each task includes unit tests):
 10. `internal/handler` — auth, account, file, admin handlers 🛠 (HTTP DTO mapping in place)
 11. `internal/server` — Gin router, route registration, graceful shutdown ✅
 12. `cmd/serve.go`, `cmd/config.go`, `cmd/status.go` ✅ (serve done)
-13. Integration tests 🛠 (authenticated register → login → upload → list → download route flow covered with a small file; file API authentication bypass, invalid token, and cross-user isolation boundaries covered)
+13. Integration tests 🛠 (authenticated register → login → upload → list → download route flow covered with a small file; authentication bypass, invalid token, concealed cross-user resources, and strict delete boundaries covered)
 14. Architecture boundary tests ✅
 
 ## Future

internal/handler/file_test.go

@@ -588,6 +588,16 @@ func TestFileHandler_Delete(t *testing.T) {
 		t.Errorf("status = %d, want %d; body = %s", rec.Code, http.StatusNoContent, rec.Body.String())
 	}
 
+	// Repeated deletes return not found.
+	req = httptest.NewRequest(http.MethodDelete, "/api/v1/files/"+uploaded.ID, nil)
+	req.Header.Set(testUserIDHeader, "user1")
+	rec = httptest.NewRecorder()
+	r.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusNotFound {
+		t.Errorf("repeated delete status = %d, want %d; body = %s", rec.Code, http.StatusNotFound, rec.Body.String())
+	}
+
 	// Verify gone.
 	req = httptest.NewRequest(http.MethodGet, "/api/v1/files/"+uploaded.ID, nil)
 	req.Header.Set(testUserIDHeader, "user1")
@@ -599,7 +609,20 @@ func TestFileHandler_Delete(t *testing.T) {
 	}
 }
 
-func TestFileHandler_ForbiddenAccess(t *testing.T) {
+func TestFileHandler_DeleteMissingReturnsNotFound(t *testing.T) {
+	r := setupFileRouter(t)
+
+	req := httptest.NewRequest(http.MethodDelete, "/api/v1/files/missing-file", nil)
+	req.Header.Set(testUserIDHeader, "user1")
+	rec := httptest.NewRecorder()
+	r.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusNotFound {
+		t.Errorf("status = %d, want %d; body = %s", rec.Code, http.StatusNotFound, rec.Body.String())
+	}
+}
+
+func TestFileHandler_CrossUserAccessReturnsNotFound(t *testing.T) {
 	r := setupFileRouter(t)
 
 	// Upload as user1.
@@ -624,7 +647,13 @@ func TestFileHandler_ForbiddenAccess(t *testing.T) {
 	rec = httptest.NewRecorder()
 	r.ServeHTTP(rec, req)
 
-	if rec.Code != http.StatusForbidden {
+	if rec.Code != http.StatusNotFound {
-		t.Errorf("status = %d, want %d", rec.Code, http.StatusForbidden)
+		t.Errorf("status = %d, want %d", rec.Code, http.StatusNotFound)
+	}
+	if !strings.Contains(rec.Body.String(), "file not found") {
+		t.Errorf("body = %s, want file not found message", rec.Body.String())
+	}
+	if strings.Contains(rec.Body.String(), "access denied") {
+		t.Errorf("body leaks authorization result: %s", rec.Body.String())
 	}
 }

internal/repository/file.go

@@ -115,9 +115,15 @@ func (r *fileRepository) Update(ctx context.Context, file *model.File) error {
 }
 
 func (r *fileRepository) Delete(ctx context.Context, id string) error {
-	result := r.db.WithContext(ctx).Model(&model.File{}).Where("id = ?", id).Update("status", model.StatusUserDeleted)
+	result := r.db.WithContext(ctx).
+		Model(&model.File{}).
+		Where("id = ? AND status = ?", id, model.StatusActive).
+		Update("status", model.StatusUserDeleted)
 	if result.Error != nil {
 		return result.Error
 	}
+	if result.RowsAffected == 0 {
+		return model.ErrNotFound
+	}
 	return nil
 }

internal/repository/file_test.go

@@ -2,6 +2,7 @@ package repository
 
 import (
 	"context"
+	"errors"
 	"testing"
 
 	"gorm.io/driver/sqlite"
@@ -259,7 +260,7 @@ func TestFileRepository_StatusFilter(t *testing.T) {
 	}
 }
 
-func TestFileRepository_DeleteIdempotent(t *testing.T) {
+func TestFileRepository_DeleteReturnsNotFoundAfterDeletion(t *testing.T) {
 	repo := setupFileRepo(t)
 	ctx := context.Background()
 
@@ -276,8 +277,11 @@ func TestFileRepository_DeleteIdempotent(t *testing.T) {
 	if err := repo.Delete(ctx, "file-1"); err != nil {
 		t.Fatalf("first Delete = %v", err)
 	}
-	if err := repo.Delete(ctx, "file-1"); err != nil {
+	if err := repo.Delete(ctx, "file-1"); !errors.Is(err, model.ErrNotFound) {
-		t.Fatalf("second Delete = %v", err)
+		t.Fatalf("second Delete = %v, want ErrNotFound", err)
+	}
+	if err := repo.Delete(ctx, "missing-file"); !errors.Is(err, model.ErrNotFound) {
+		t.Fatalf("missing Delete = %v, want ErrNotFound", err)
 	}
 }
 

internal/server/file_integration_test.go

@@ -7,6 +7,7 @@ import (
 	"mime/multipart"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 	"time"
 
@@ -44,6 +45,32 @@ type fileIntegrationList struct {
 	Total int64                 `json:"total"`
 }
 
+func assertFileIntegrationNotFound(
+	t *testing.T,
+	rec *httptest.ResponseRecorder,
+	wantMessage string,
+) {
+	t.Helper()
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("status=%d, want %d; body=%s", rec.Code, http.StatusNotFound, rec.Body.String())
+	}
+
+	var response struct {
+		Error struct {
+			Message string `json:"message"`
+		} `json:"error"`
+	}
+	if err := json.Unmarshal(rec.Body.Bytes(), &response); err != nil {
+		t.Fatalf("decode error response: %v", err)
+	}
+	if response.Error.Message != wantMessage {
+		t.Fatalf("message=%q, want %q", response.Error.Message, wantMessage)
+	}
+	if strings.Contains(rec.Body.String(), "access denied") {
+		t.Fatalf("response leaks authorization result: %s", rec.Body.String())
+	}
+}
+
 func newFileIntegrationFixture(t *testing.T) *fileIntegrationFixture {
 	t.Helper()
 
@@ -402,6 +429,7 @@ func TestFileRoutesEnforceAuthenticatedOwnership(t *testing.T) {
 	if otherList.Total != 0 || len(otherList.Files) != 0 {
 		t.Fatalf("other user's root list=%+v, want empty list", otherList)
 	}
+	otherFile := fixture.uploadFile(t, otherTokens.AccessToken, "other.txt", []byte("other content"))
 
 	createBody, err := json.Marshal(map[string]any{
 		"name":      "intrusion",
@@ -410,18 +438,81 @@ func TestFileRoutesEnforceAuthenticatedOwnership(t *testing.T) {
 	if err != nil {
 		t.Fatalf("marshal cross-owner create body: %v", err)
 	}
-	createRequest := newAuthenticatedFileRequest(
+	moveBody, err := json.Marshal(map[string]any{"parent_id": privateDir.ID})
-		http.MethodPost,
+	if err != nil {
-		"/api/v1/files",
+		t.Fatalf("marshal cross-owner move body: %v", err)
-		bytes.NewReader(createBody),
+	}
+	parentRequests := []struct {
+		name       string
+		newRequest func(*testing.T) *http.Request
+	}{
+		{
+			name: "list",
+			newRequest: func(*testing.T) *http.Request {
+				return newAuthenticatedFileRequest(
+					http.MethodGet,
+					"/api/v1/files?parent_id="+privateDir.ID,
+					nil,
+					otherTokens.AccessToken,
+				)
+			},
+		},
+		{
+			name: "create directory",
+			newRequest: func(*testing.T) *http.Request {
+				req := newAuthenticatedFileRequest(
+					http.MethodPost,
+					"/api/v1/files",
+					bytes.NewReader(createBody),
+					otherTokens.AccessToken,
+				)
+				req.Header.Set("Content-Type", "application/json")
+				return req
+			},
+		},
+		{
+			name: "upload",
+			newRequest: func(t *testing.T) *http.Request {
+				return newFileUploadRequest(
+					t,
+					"/api/v1/files?parent_id="+privateDir.ID,
+					otherTokens.AccessToken,
+					"intrusion.txt",
+					[]byte("must not persist"),
+				)
+			},
+		},
+		{
+			name: "move",
+			newRequest: func(*testing.T) *http.Request {
+				req := newAuthenticatedFileRequest(
+					http.MethodPut,
+					"/api/v1/files/"+otherFile.ID,
+					bytes.NewReader(moveBody),
+					otherTokens.AccessToken,
+				)
+				req.Header.Set("Content-Type", "application/json")
+				return req
+			},
+		},
+	}
+
+	for _, request := range parentRequests {
+		t.Run("parent/"+request.name, func(t *testing.T) {
+			rec := httptest.NewRecorder()
+			fixture.router.ServeHTTP(rec, request.newRequest(t))
+			assertFileIntegrationNotFound(t, rec, "parent directory not found")
+		})
+	}
+	missingParentRequest := newAuthenticatedFileRequest(
+		http.MethodGet,
+		"/api/v1/files?parent_id=missing-directory",
+		nil,
 		otherTokens.AccessToken,
 	)
-	createRequest.Header.Set("Content-Type", "application/json")
+	missingParentResponse := httptest.NewRecorder()
-	createResponse := httptest.NewRecorder()
+	fixture.router.ServeHTTP(missingParentResponse, missingParentRequest)
-	fixture.router.ServeHTTP(createResponse, createRequest)
+	assertFileIntegrationNotFound(t, missingParentResponse, "parent directory not found")
-	if createResponse.Code != http.StatusForbidden {
-		t.Fatalf("cross-owner create: status=%d, want %d; body=%s", createResponse.Code, http.StatusForbidden, createResponse.Body.String())
-	}
 
 	updateBody := []byte(`{"name":"stolen.txt"}`)
 	requests := []struct {
@@ -451,9 +542,7 @@ func TestFileRoutesEnforceAuthenticatedOwnership(t *testing.T) {
 			rec := httptest.NewRecorder()
 			fixture.router.ServeHTTP(rec, req)
 
-			if rec.Code != http.StatusForbidden {
+			assertFileIntegrationNotFound(t, rec, "file not found")
-				t.Fatalf("status=%d, want %d; body=%s", rec.Code, http.StatusForbidden, rec.Body.String())
-			}
 		})
 	}
 
@@ -499,4 +588,38 @@ func TestFileRoutesEnforceAuthenticatedOwnership(t *testing.T) {
 	if dirList.Total != 0 || len(dirList.Files) != 0 {
 		t.Fatalf("private directory after rejected create=%+v, want empty list", dirList)
 	}
+
+	otherRootList := fixture.listFiles(t, otherTokens.AccessToken, "/api/v1/files")
+	if otherRootList.Total != 1 || len(otherRootList.Files) != 1 || otherRootList.Files[0].ID != otherFile.ID {
+		t.Fatalf("other user's root list after rejected move=%+v, want original file", otherRootList)
+	}
+}
+
+func TestFileDeleteReturnsNotFoundForMissingAndDeletedFiles(t *testing.T) {
+	fixture := newFileIntegrationFixture(t)
+	_, tokens := fixture.registerAndLogin(t, "delete-user")
+
+	missingRequest := newAuthenticatedFileRequest(
+		http.MethodDelete,
+		"/api/v1/files/missing-file",
+		nil,
+		tokens.AccessToken,
+	)
+	missingResponse := httptest.NewRecorder()
+	fixture.router.ServeHTTP(missingResponse, missingRequest)
+	assertFileIntegrationNotFound(t, missingResponse, "file not found")
+
+	uploaded := fixture.uploadFile(t, tokens.AccessToken, "delete-me.txt", []byte("delete content"))
+	deleteTarget := "/api/v1/files/" + uploaded.ID
+	firstRequest := newAuthenticatedFileRequest(http.MethodDelete, deleteTarget, nil, tokens.AccessToken)
+	firstResponse := httptest.NewRecorder()
+	fixture.router.ServeHTTP(firstResponse, firstRequest)
+	if firstResponse.Code != http.StatusNoContent {
+		t.Fatalf("first delete: status=%d, want %d; body=%s", firstResponse.Code, http.StatusNoContent, firstResponse.Body.String())
+	}
+
+	secondRequest := newAuthenticatedFileRequest(http.MethodDelete, deleteTarget, nil, tokens.AccessToken)
+	secondResponse := httptest.NewRecorder()
+	fixture.router.ServeHTTP(secondResponse, secondRequest)
+	assertFileIntegrationNotFound(t, secondResponse, "file not found")
 }

internal/service/file.go

@@ -304,10 +304,6 @@ func (s *FileService) Update(ctx context.Context, userID, fileID string, newName
 func (s *FileService) Delete(ctx context.Context, userID, fileID string) error {
 	file, err := s.getOwnedFile(ctx, userID, fileID)
 	if err != nil {
-		var ae *model.AppError
-		if errors.As(err, &ae) && errors.Is(ae.Err, model.ErrNotFound) {
-			return nil // idempotent: already deleted
-		}
 		return err
 	}
 
@@ -323,6 +319,9 @@ func (s *FileService) Delete(ctx context.Context, userID, fileID string) error {
 	}
 
 	if err := s.fileRepo.Delete(ctx, fileID); err != nil {
+		if errors.Is(err, model.ErrNotFound) {
+			return model.NewNotFoundError("file not found", model.ErrNotFound)
+		}
 		return model.NewInternalError("delete file record", err)
 	}
 
@@ -378,7 +377,7 @@ func (s *FileService) getOwnedFile(ctx context.Context, userID, fileID string) (
 	}
 
 	if file.UserID != userID {
-		return nil, model.NewForbiddenError("access denied", model.ErrForbidden)
+		return nil, model.NewNotFoundError("file not found", model.ErrNotFound)
 	}
 
 	return file, nil
@@ -395,7 +394,7 @@ func (s *FileService) verifyParent(ctx context.Context, userID, parentID string)
 	}
 
 	if parent.UserID != userID {
-		return model.NewForbiddenError("access denied", model.ErrForbidden)
+		return model.NewNotFoundError("parent directory not found", model.ErrNotFound)
 	}
 
 	if !parent.IsDir {

internal/service/file_test.go

@@ -32,6 +32,18 @@ func assertAppError(t *testing.T, err error, wantKind model.ErrorKind) bool {
 	return true
 }
 
+func assertAppErrorMessage(t *testing.T, err error, wantKind model.ErrorKind, wantMessage string) {
+	t.Helper()
+	if !assertAppError(t, err, wantKind) {
+		return
+	}
+	var ae *model.AppError
+	errors.As(err, &ae)
+	if ae.Message != wantMessage {
+		t.Errorf("message = %q, want %q", ae.Message, wantMessage)
+	}
+}
+
 // memStorage is an in-memory implementation of storage.StorageBackend for tests.
 type memStorage struct {
 	mu    sync.RWMutex
@@ -274,7 +286,7 @@ func TestFileService_Download(t *testing.T) {
 	}
 }
 
-func TestFileService_DownloadForbidden(t *testing.T) {
+func TestFileService_DownloadReturnsNotFoundForOtherUser(t *testing.T) {
 	svc := setupFileService(t)
 	ctx := context.Background()
 
@@ -284,7 +296,7 @@ func TestFileService_DownloadForbidden(t *testing.T) {
 	}
 
 	_, _, err = svc.Download(ctx, "user2", info.ID)
-	assertAppError(t, err, model.KindPermissionDenied)
+	assertAppErrorMessage(t, err, model.KindNotFound, "file not found")
 }
 
 func TestFileService_DownloadDirectory(t *testing.T) {
@@ -328,7 +340,7 @@ func TestFileService_GetNotFound(t *testing.T) {
 	assertAppError(t, err, model.KindNotFound)
 }
 
-func TestFileService_GetForbidden(t *testing.T) {
+func TestFileService_GetReturnsNotFoundForOtherUser(t *testing.T) {
 	svc := setupFileService(t)
 	ctx := context.Background()
 
@@ -338,7 +350,7 @@ func TestFileService_GetForbidden(t *testing.T) {
 	}
 
 	_, err = svc.Get(ctx, "user2", info.ID)
-	assertAppError(t, err, model.KindPermissionDenied)
+	assertAppErrorMessage(t, err, model.KindNotFound, "file not found")
 }
 
 func TestFileService_List(t *testing.T) {
@@ -395,6 +407,19 @@ func TestFileService_Update(t *testing.T) {
 	}
 }
 
+func TestFileService_UpdateReturnsNotFoundForOtherUser(t *testing.T) {
+	svc := setupFileService(t)
+	ctx := context.Background()
+
+	info, err := svc.Upload(ctx, "user1", nil, "private.txt", strings.NewReader("data"))
+	if err != nil {
+		t.Fatalf("Upload = %v", err)
+	}
+
+	_, err = svc.Update(ctx, "user2", info.ID, "stolen.txt", nil)
+	assertAppErrorMessage(t, err, model.KindNotFound, "file not found")
+}
+
 func TestFileService_UpdateMove(t *testing.T) {
 	svc := setupFileService(t)
 	ctx := context.Background()
@@ -458,7 +483,7 @@ func TestFileService_DeleteNonEmptyDirectory(t *testing.T) {
 	}
 }
 
-func TestFileService_DeleteForbidden(t *testing.T) {
+func TestFileService_DeleteReturnsNotFoundForOtherUser(t *testing.T) {
 	svc := setupFileService(t)
 	ctx := context.Background()
 
@@ -468,7 +493,14 @@ func TestFileService_DeleteForbidden(t *testing.T) {
 	}
 
 	err = svc.Delete(ctx, "user2", info.ID)
-	assertAppError(t, err, model.KindPermissionDenied)
+	assertAppErrorMessage(t, err, model.KindNotFound, "file not found")
+}
+
+func TestFileService_DeleteReturnsNotFoundForMissingFile(t *testing.T) {
+	svc := setupFileService(t)
+
+	err := svc.Delete(context.Background(), "user1", "missing-file")
+	assertAppErrorMessage(t, err, model.KindNotFound, "file not found")
 }
 
 func TestFileService_CreateDir(t *testing.T) {
@@ -502,7 +534,7 @@ func TestFileService_CreateDirDuplicateName(t *testing.T) {
 	}
 }
 
-func TestFileService_VerifyParentForbidden(t *testing.T) {
+func TestFileService_ParentOperationsReturnNotFoundForOtherUser(t *testing.T) {
 	svc := setupFileService(t)
 	ctx := context.Background()
 
@@ -510,9 +542,50 @@ func TestFileService_VerifyParentForbidden(t *testing.T) {
 	if err != nil {
 		t.Fatalf("CreateDir = %v", err)
 	}
+	otherFile, err := svc.Upload(ctx, "user2", nil, "other.txt", strings.NewReader("data"))
+	if err != nil {
+		t.Fatalf("Upload other file = %v", err)
+	}
 
-	_, err = svc.Upload(ctx, "user2", &dir.ID, "stolen.txt", strings.NewReader("data"))
+	tests := []struct {
-	assertAppError(t, err, model.KindPermissionDenied)
+		name string
+		run  func() error
+	}{
+		{
+			name: "list",
+			run: func() error {
+				_, err := svc.List(ctx, "user2", &dir.ID, 0, 50)
+				return err
+			},
+		},
+		{
+			name: "upload",
+			run: func() error {
+				_, err := svc.Upload(ctx, "user2", &dir.ID, "stolen.txt", strings.NewReader("data"))
+				return err
+			},
+		},
+		{
+			name: "create directory",
+			run: func() error {
+				_, err := svc.CreateDir(ctx, "user2", &dir.ID, "stolen-dir")
+				return err
+			},
+		},
+		{
+			name: "move",
+			run: func() error {
+				_, err := svc.Update(ctx, "user2", otherFile.ID, "", &dir.ID)
+				return err
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assertAppErrorMessage(t, tt.run(), model.KindNotFound, "parent directory not found")
+		})
+	}
 }
 
 func TestFileService_SoftDelete(t *testing.T) {
@@ -562,7 +635,7 @@ func TestFileService_SoftDeleteKeepsStorage(t *testing.T) {
 	}
 }
 
-func TestFileService_SoftDeleteIdempotent(t *testing.T) {
+func TestFileService_SoftDeleteRepeatedReturnsNotFound(t *testing.T) {
 	svc := setupFileService(t)
 	ctx := context.Background()
 
@@ -574,12 +647,11 @@ func TestFileService_SoftDeleteIdempotent(t *testing.T) {
 	if err := svc.Delete(ctx, "user1", info.ID); err != nil {
 		t.Fatalf("first Delete = %v", err)
 	}
-	if err := svc.Delete(ctx, "user1", info.ID); err != nil {
+	err = svc.Delete(ctx, "user1", info.ID)
-		t.Fatalf("second Delete should be idempotent, got: %v", err)
+	assertAppErrorMessage(t, err, model.KindNotFound, "file not found")
-	}
 }
 
-func TestFileService_SoftDeleteForbidden(t *testing.T) {
+func TestFileService_SoftDeleteReturnsNotFoundForOtherUser(t *testing.T) {
 	svc := setupFileService(t)
 	ctx := context.Background()
 
@@ -589,5 +661,5 @@ func TestFileService_SoftDeleteForbidden(t *testing.T) {
 	}
 
 	err = svc.Delete(ctx, "user2", info.ID)
-	assertAppError(t, err, model.KindPermissionDenied)
+	assertAppErrorMessage(t, err, model.KindNotFound, "file not found")
 }