fix(backend): harden write registrar boundaries

backend/internal/logic/files/service_test.go

@@ -1,12 +1,37 @@
 package files
 
 import (
+	"errors"
+	"io/fs"
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/require"
 )
 
+type failingReader struct {
+	sent bool
+}
+
+func (r *failingReader) Read(buffer []byte) (int, error) {
+	if !r.sent {
+		r.sent = true
+		return copy(buffer, "partial"), nil
+	}
+	return 0, errors.New("copy failed")
+}
+
+type closeFailingFile struct {
+	*os.File
+}
+
+func (f *closeFailingFile) Close() error {
+	_ = f.File.Close()
+	return errors.New("close failed")
+}
+
 func TestSaveStoresFileUnderProjectDirectory(t *testing.T) {
 	service := NewService(t.TempDir())
 
@@ -27,3 +52,57 @@ func TestSaveNeutralizesPathTraversal(t *testing.T) {
 	require.Equal(t, "secret.txt", stored.OriginalName)
 	require.Contains(t, stored.RelativePath, "projects/12/")
 }
+
+func TestSaveRemovesTemporaryAndPartialFilesWhenCopyFails(t *testing.T) {
+	storageRoot := t.TempDir()
+	service := NewService(storageRoot)
+
+	_, err := service.Save(12, "broken.bin", &failingReader{})
+
+	require.ErrorContains(t, err, "copy failed")
+	requireNoStoredFiles(t, storageRoot)
+}
+
+func TestSaveRemovesTemporaryFileWhenCloseFails(t *testing.T) {
+	storageRoot := t.TempDir()
+	service := NewService(storageRoot)
+	service.createTemp = func(directory, pattern string) (stagedFile, error) {
+		file, err := os.CreateTemp(directory, pattern)
+		if err != nil {
+			return nil, err
+		}
+		return &closeFailingFile{File: file}, nil
+	}
+
+	_, err := service.Save(12, "broken.bin", strings.NewReader("content"))
+
+	require.ErrorContains(t, err, "close failed")
+	requireNoStoredFiles(t, storageRoot)
+}
+
+func TestSaveRemovesTemporaryAndPartialFilesWhenRenameFails(t *testing.T) {
+	storageRoot := t.TempDir()
+	service := NewService(storageRoot)
+	service.rename = func(oldPath, newPath string) error {
+		require.NoError(t, os.WriteFile(newPath, []byte("partial final"), 0o600))
+		return errors.New("rename failed")
+	}
+
+	_, err := service.Save(12, "broken.bin", strings.NewReader("content"))
+
+	require.ErrorContains(t, err, "rename failed")
+	requireNoStoredFiles(t, storageRoot)
+}
+
+func requireNoStoredFiles(t *testing.T, storageRoot string) {
+	t.Helper()
+	require.NoError(t, filepath.WalkDir(storageRoot, func(path string, entry fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if path != storageRoot && !entry.IsDir() {
+			t.Fatalf("unexpected stored file after failure: %s", path)
+		}
+		return nil
+	}))
+}