diff --git a/.golangci.yaml b/.golangci.yaml
index 6360fd1..2cd3e48 100644
--- a/.golangci.yaml
+++ b/.golangci.yaml
@@ -164,6 +164,11 @@ issues:
     - path: internal/view/(.+)_test\.go
       linters:
         - testpackage
+    - path: fake_(.+)\.go
+      linters:
+        - revive
+        - goconst
+        - wrapcheck
   include:
     - EXC0012
     - EXC0014
diff --git a/internal/fileupload/lowlevel/fake_client.go b/internal/fileupload/lowlevel/fake_client.go
new file mode 100644
index 0000000..9a4d66e
--- /dev/null
+++ b/internal/fileupload/lowlevel/fake_client.go
@@ -0,0 +1,137 @@
+package lowlevel
+
+import (
+	"context"
+	"fmt"
+	"io"
+
+	"github.com/google/uuid"
+)
+
+type LoadedFile struct {
+	Path    string
+	Content string
+}
+
+// revisionState holds the in-memory state for a single revision.
+type revisionState struct {
+	orgID  OrgID
+	sealed bool
+	files  []LoadedFile
+}
+
+// FakeSealableClient is a mock implementation of the SealableClient for testing.
+// It tracks revisions in memory and enforces the revision lifecycle (create -> upload -> seal).
+type FakeSealableClient struct {
+	cfg       FakeClientConfig
+	revisions map[RevisionID]*revisionState
+}
+
+type FakeClientConfig struct {
+	Limits
+}
+
+// NewFakeSealableClient creates a new instance of the fake client.
+func NewFakeSealableClient(cfg FakeClientConfig) *FakeSealableClient {
+	return &FakeSealableClient{
+		cfg:       cfg,
+		revisions: make(map[RevisionID]*revisionState),
+	}
+}
+
+func (f *FakeSealableClient) CreateRevision(_ context.Context, orgID OrgID) (*UploadRevisionResponseBody, error) {
+	newRevisionID := uuid.New()
+	f.revisions[newRevisionID] = &revisionState{
+		orgID:  orgID,
+		sealed: false,
+	}
+
+	return &UploadRevisionResponseBody{
+		Data: UploadRevisionResponseData{
+			ID: newRevisionID,
+		},
+	}, nil
+}
+
+func (f *FakeSealableClient) UploadFiles(_ context.Context, orgID OrgID, revisionID RevisionID, files []UploadFile) error {
+	rev, ok := f.revisions[revisionID]
+	if !ok {
+		return fmt.Errorf("revision %s not found", revisionID)
+	}
+
+	if rev.orgID != orgID {
+		return fmt.Errorf("orgID mismatch for revision %s", revisionID)
+	}
+
+	if rev.sealed {
+		return fmt.Errorf("revision %s is sealed and cannot be modified", revisionID)
+	}
+
+	if len(files) > f.cfg.FileCountLimit {
+		return NewFileCountLimitError(len(files), f.cfg.FileCountLimit)
+	}
+
+	if len(files) == 0 {
+		return ErrNoFilesProvided
+	}
+
+	for _, file := range files {
+		fileInfo, err := file.File.Stat()
+		if err != nil {
+			return NewFileAccessError(file.Path, err)
+		}
+
+		if fileInfo.IsDir() {
+			return NewDirectoryError(file.Path)
+		}
+
+		if fileInfo.Size() > f.cfg.FileSizeLimit {
+			return NewFileSizeLimitError(file.Path, fileInfo.Size(), f.cfg.FileSizeLimit)
+		}
+	}
+
+	for _, file := range files {
+		bts, err := io.ReadAll(file.File)
+		if err != nil {
+			return err
+		}
+		rev.files = append(rev.files, LoadedFile{
+			Path:    file.Path,
+			Content: string(bts),
+		})
+	}
+	return nil
+}
+
+func (f *FakeSealableClient) SealRevision(_ context.Context, orgID OrgID, revisionID RevisionID) (*SealUploadRevisionResponseBody, error) {
+	rev, ok := f.revisions[revisionID]
+	if !ok {
+		return nil, fmt.Errorf("revision %s not found", revisionID)
+	}
+
+	if rev.orgID != orgID {
+		return nil, fmt.Errorf("orgID mismatch for revision %s", revisionID)
+	}
+
+	rev.sealed = true
+	return &SealUploadRevisionResponseBody{}, nil
+}
+
+// GetSealedRevisionFiles is a test helper to retrieve files for a sealed revision.
+// It is not part of the SealableClient interface.
+func (f *FakeSealableClient) GetSealedRevisionFiles(revisionID RevisionID) ([]LoadedFile, error) {
+	rev, ok := f.revisions[revisionID]
+	if !ok {
+		return nil, fmt.Errorf("revision %s not found", revisionID)
+	}
+
+	if !rev.sealed {
+		return nil, fmt.Errorf("revision %s is not sealed", revisionID)
+	}
+
+	return rev.files, nil
+}
+
+func (f *FakeSealableClient) GetLimits() Limits {
+	return f.cfg.Limits
+}