feat(backend): handle processing errors and add PWA routes

- Block file downloads and previews with a 424 StatusFailedDependency if file processing failed or the box has issues.
- Register routes for `/service-worker.js` and `/share-target` to support PWA features.
- Update README.md with an AI usage disclosure.

backend/libs/services/resumable.go

@@ -369,19 +369,20 @@ func (s *UploadService) FinalizeProcessingResumableSession(ctx context.Context,
 	}
 	backend, err := s.storage.Backend(box.StorageBackendID)
 	if err != nil {
+		_ = s.markProcessingBoxFailed(box, err)
 		return UploadResult{}, err
 	}
 	for i, incoming := range staged {
 		source, err := incoming.Open()
 		if err != nil {
+			_ = s.markProcessingBoxFailed(box, err)
 			return UploadResult{}, err
 		}
 		file := box.Files[i]
 		if err := s.writeUploadedObject(ctx, backend, file.ObjectKey, source, incoming.Size(), 0, incoming.ContentType()); err != nil {
 			source.Close()
 			_ = backend.Delete(context.Background(), file.ObjectKey)
-			box.Files[i].ProcessingError = err.Error()
-			_ = s.saveBoxRecord(box)
+			_ = s.markProcessingBoxFailed(box, err)
 			return UploadResult{}, err
 		}
 		source.Close()
@@ -406,6 +407,35 @@ func (s *UploadService) FinalizeProcessingResumableSession(ctx context.Context,
 	return s.resultForBox(box, ""), nil
 }
 
+func (s *UploadService) markProcessingBoxFailed(box Box, cause error) error {
+	message := "upload processing failed"
+	if cause != nil && strings.TrimSpace(cause.Error()) != "" {
+		message = cause.Error()
+	}
+	s.logger.Warn("resumable upload box marked failed", "source", "user-upload", "severity", "warn", "code", 4021, "box_id", box.ID, "backend_id", s.BoxStorageBackendID(box), "files", len(box.Files), "error", message)
+	now := time.Now().UTC()
+	box.Trouble = true
+	box.TroubleReason = message
+	for i := range box.Files {
+		if box.Files[i].Processing || box.Files[i].ProcessingError == "" {
+			box.Files[i].Processing = false
+			box.Files[i].ProcessingError = message
+			if box.Files[i].UploadedAt.IsZero() {
+				box.Files[i].UploadedAt = now
+			}
+		}
+	}
+	if err := s.saveBoxRecord(box); err != nil {
+		s.logger.Warn("failed to save failed upload box state", "source", "user-upload", "severity", "warn", "code", 4022, "box_id", box.ID, "backend_id", s.BoxStorageBackendID(box), "error", err.Error())
+		return err
+	}
+	if err := s.writeBoxMetadata(box); err != nil {
+		s.logger.Warn("failed to write failed upload box metadata", "source", "user-upload", "severity", "warn", "code", 4023, "box_id", box.ID, "backend_id", s.BoxStorageBackendID(box), "error", err.Error())
+		return err
+	}
+	return nil
+}
+
 func (s *UploadService) CompleteUploadedResumableSession(ctx context.Context, sessionID string) (UploadResult, ResumableSession, error) {
 	session, err := s.GetResumableSession(sessionID)
 	if err != nil {

backend/libs/services/storage_s3.go

@@ -35,26 +35,35 @@ func (b *s3StorageBackend) ID() string   { return b.cfg.ID }
 func (b *s3StorageBackend) Type() string { return StorageBackendS3 }
 
 func (b *s3StorageBackend) Put(ctx context.Context, key string, body io.Reader, size int64, contentType string) error {
+	cleanKey := cleanObjectKey(key)
 	opts := minio.PutObjectOptions{ContentType: contentType}
-	_, err := b.client.PutObject(ctx, b.cfg.Bucket, cleanObjectKey(key), body, size, opts)
-	return err
+	_, err := b.client.PutObject(ctx, b.cfg.Bucket, cleanKey, body, size, opts)
+	if err != nil {
+		return fmt.Errorf("s3 put object %q in bucket %q failed: %w", cleanKey, b.cfg.Bucket, err)
+	}
+	return nil
 }
 
 func (b *s3StorageBackend) Get(ctx context.Context, key string) (StorageObject, error) {
-	object, err := b.client.GetObject(ctx, b.cfg.Bucket, cleanObjectKey(key), minio.GetObjectOptions{})
+	cleanKey := cleanObjectKey(key)
+	object, err := b.client.GetObject(ctx, b.cfg.Bucket, cleanKey, minio.GetObjectOptions{})
 	if err != nil {
-		return StorageObject{}, err
+		return StorageObject{}, fmt.Errorf("s3 get object %q from bucket %q failed: %w", cleanKey, b.cfg.Bucket, err)
 	}
 	info, err := object.Stat()
 	if err != nil {
 		object.Close()
-		return StorageObject{}, err
+		return StorageObject{}, fmt.Errorf("s3 stat object %q in bucket %q failed: %w", cleanKey, b.cfg.Bucket, err)
 	}
 	return StorageObject{Key: key, Size: info.Size, ContentType: info.ContentType, ModTime: info.LastModified, Body: object}, nil
 }
 
 func (b *s3StorageBackend) Delete(ctx context.Context, key string) error {
-	return b.client.RemoveObject(ctx, b.cfg.Bucket, cleanObjectKey(key), minio.RemoveObjectOptions{})
+	cleanKey := cleanObjectKey(key)
+	if err := b.client.RemoveObject(ctx, b.cfg.Bucket, cleanKey, minio.RemoveObjectOptions{}); err != nil {
+		return fmt.Errorf("s3 delete object %q from bucket %q failed: %w", cleanKey, b.cfg.Bucket, err)
+	}
+	return nil
 }
 
 func (b *s3StorageBackend) DeletePrefix(ctx context.Context, prefix string) error {
@@ -62,7 +71,7 @@ func (b *s3StorageBackend) DeletePrefix(ctx context.Context, prefix string) erro
 	objects := b.client.ListObjects(ctx, b.cfg.Bucket, minio.ListObjectsOptions{Prefix: prefix, Recursive: true})
 	for object := range objects {
 		if object.Err != nil {
-			return object.Err
+			return fmt.Errorf("s3 list prefix %q in bucket %q failed: %w", prefix, b.cfg.Bucket, object.Err)
 		}
 		if err := b.Delete(ctx, object.Key); err != nil {
 			return err
@@ -75,7 +84,7 @@ func (b *s3StorageBackend) Usage(ctx context.Context) (int64, error) {
 	var total int64
 	for object := range b.client.ListObjects(ctx, b.cfg.Bucket, minio.ListObjectsOptions{Recursive: true}) {
 		if object.Err != nil {
-			return 0, object.Err
+			return 0, fmt.Errorf("s3 usage list bucket %q failed: %w", b.cfg.Bucket, object.Err)
 		}
 		total += object.Size
 	}
@@ -85,7 +94,7 @@ func (b *s3StorageBackend) Usage(ctx context.Context) (int64, error) {
 func (b *s3StorageBackend) Test(ctx context.Context) error {
 	exists, err := b.client.BucketExists(ctx, b.cfg.Bucket)
 	if err != nil {
-		return err
+		return fmt.Errorf("s3 bucket check for %q failed: %w", b.cfg.Bucket, err)
 	}
 	if !exists {
 		return fmt.Errorf("bucket %q does not exist", b.cfg.Bucket)

backend/libs/services/upload.go

@@ -117,6 +117,8 @@ type Box struct {
 	Obfuscate        bool      `json:"obfuscate"`
 	CreatorIP        string    `json:"creatorIp,omitempty"`
 	StorageBackendID string    `json:"storageBackendId,omitempty"`
+	Trouble          bool      `json:"trouble,omitempty"`
+	TroubleReason    string    `json:"troubleReason,omitempty"`
 	Files            []File    `json:"files"`
 }
 
@@ -139,6 +141,37 @@ type File struct {
 	UploadedAt              time.Time `json:"uploadedAt"`
 }
 
+func BoxHasTrouble(box Box) bool {
+	if box.Trouble || strings.TrimSpace(box.TroubleReason) != "" {
+		return true
+	}
+	for _, file := range box.Files {
+		if FileHasTrouble(file) {
+			return true
+		}
+	}
+	return false
+}
+
+func BoxTroubleReason(box Box) string {
+	if strings.TrimSpace(box.TroubleReason) != "" {
+		return box.TroubleReason
+	}
+	for _, file := range box.Files {
+		if strings.TrimSpace(file.ProcessingError) != "" {
+			return file.ProcessingError
+		}
+	}
+	if box.Trouble {
+		return "box has failed processing"
+	}
+	return ""
+}
+
+func FileHasTrouble(file File) bool {
+	return strings.TrimSpace(file.ProcessingError) != ""
+}
+
 type UploadResult struct {
 	BoxID        string       `json:"boxId"`
 	BoxURL       string       `json:"boxUrl"`

backend/libs/services/upload_test.go

@@ -230,6 +230,47 @@ func TestResumableCompleteRejectsMissingChunks(t *testing.T) {
 	}
 }
 
+func TestProcessingResumableFailureMarksBoxFailed(t *testing.T) {
+	service := newTestUploadService(t)
+	session, err := service.CreateResumableSession([]ResumableFileInput{{
+		Name:        "note.txt",
+		Size:        4,
+		ContentType: "text/plain",
+	}}, UploadOptions{MaxDays: 1, StorageBackendID: "missing"}, 4, time.Hour, "")
+	if err != nil {
+		t.Fatalf("CreateResumableSession returned error: %v", err)
+	}
+	if _, err := service.PutResumableChunk(testContext(), session.ID, session.Files[0].ID, 0, strings.NewReader("note")); err != nil {
+		t.Fatalf("PutResumableChunk returned error: %v", err)
+	}
+	result, processing, err := service.CreateProcessingBoxFromResumable(session.ID)
+	if err != nil {
+		t.Fatalf("CreateProcessingBoxFromResumable returned error: %v", err)
+	}
+	if processing.Status != ResumableStatusProcessing {
+		t.Fatalf("session status = %q, want processing", processing.Status)
+	}
+	if _, err := service.FinalizeProcessingResumableSession(testContext(), session.ID); err == nil {
+		t.Fatalf("FinalizeProcessingResumableSession accepted missing backend")
+	}
+	box := getTestBox(t, service, result.BoxID)
+	if len(box.Files) != 1 {
+		t.Fatalf("box files = %+v", box.Files)
+	}
+	if box.Files[0].Processing {
+		t.Fatalf("failed file is still marked processing: %+v", box.Files[0])
+	}
+	if box.Files[0].ProcessingError == "" {
+		t.Fatalf("failed file did not store processing error: %+v", box.Files[0])
+	}
+	if !box.Trouble {
+		t.Fatalf("failed box was not marked as trouble: %+v", box)
+	}
+	if box.TroubleReason == "" {
+		t.Fatalf("failed box did not store trouble reason: %+v", box)
+	}
+}
+
 func TestResumablePartialCompleteKeepsOnlyFinishedFiles(t *testing.T) {
 	service := newTestUploadService(t)
 	session, err := service.CreateResumableSession([]ResumableFileInput{