Consolidate path safety, temp downloads, and cleanup validation helpers

internal/adapters/storage/temp_download.go

@@ -0,0 +1,36 @@
+package storage
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// DownloadObjectToTemp downloads an object into a temporary file and returns
+// the cleaned local path.
+func DownloadObjectToTemp(ctx context.Context, store ObjectStore, key, pattern string) (string, error) {
+	if store == nil {
+		return "", fmt.Errorf("object store is required")
+	}
+	if strings.TrimSpace(pattern) == "" {
+		return "", fmt.Errorf("temp file pattern is required")
+	}
+
+	tmp, err := os.CreateTemp("", pattern)
+	if err != nil {
+		return "", fmt.Errorf("create temp file: %w", err)
+	}
+	path := tmp.Name()
+	if err := tmp.Close(); err != nil {
+		_ = os.Remove(path)
+		return "", fmt.Errorf("close temp file: %w", err)
+	}
+
+	if err := store.Download(ctx, key, path); err != nil {
+		_ = os.Remove(path)
+		return "", err
+	}
+	return filepath.Clean(path), nil
+}

internal/adapters/storage/temp_download_test.go

@@ -0,0 +1,69 @@
+package storage
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestDownloadObjectToTempSuccess(t *testing.T) {
+	store := &FakeBackend{}
+	store.SeedObject(FakeObject{Key: "sessions/a/current/run_id.txt", Data: []byte("run-123\n")})
+
+	path, err := DownloadObjectToTemp(context.Background(), store, "sessions/a/current/run_id.txt", "narratio-test-*.txt")
+	if err != nil {
+		t.Fatalf("DownloadObjectToTemp() error = %v", err)
+	}
+	t.Cleanup(func() { _ = os.Remove(path) })
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("ReadFile() error = %v", err)
+	}
+	if string(data) != "run-123\n" {
+		t.Fatalf("downloaded data = %q, want %q", string(data), "run-123\n")
+	}
+}
+
+func TestDownloadObjectToTempFailedDownloadRemovesTempFile(t *testing.T) {
+	sentinel := errors.New("download failed")
+	store := &FakeBackend{DownloadErr: sentinel}
+	pattern := "narratio-test-fail-*.txt"
+	before, err := filepath.Glob(filepath.Join(os.TempDir(), "narratio-test-fail-*.txt"))
+	if err != nil {
+		t.Fatalf("Glob(before) error = %v", err)
+	}
+
+	path, err := DownloadObjectToTemp(context.Background(), store, "sessions/a/current/run_id.txt", pattern)
+	if !errors.Is(err, sentinel) {
+		t.Fatalf("DownloadObjectToTemp() error = %v, want %v", err, sentinel)
+	}
+	if strings.TrimSpace(path) != "" {
+		t.Fatalf("DownloadObjectToTemp() path = %q, want empty on failure", path)
+	}
+	after, err := filepath.Glob(filepath.Join(os.TempDir(), "narratio-test-fail-*.txt"))
+	if err != nil {
+		t.Fatalf("Glob(after) error = %v", err)
+	}
+	if len(after) != len(before) {
+		t.Fatalf("temp file count changed after failed download: before=%d after=%d", len(before), len(after))
+	}
+}
+
+func TestDownloadObjectToTempCallerContextWrappingPreservesCause(t *testing.T) {
+	sentinel := errors.New("object missing")
+	store := &FakeBackend{DownloadErr: sentinel}
+
+	_, err := DownloadObjectToTemp(context.Background(), store, "sessions/a/current/run_id.txt", "narratio-test-*.txt")
+	if err == nil {
+		t.Fatal("DownloadObjectToTemp() error = nil, want error")
+	}
+	err = fmt.Errorf("download run pointer failed: %w", err)
+	if !errors.Is(err, sentinel) {
+		t.Fatalf("wrapped error does not preserve sentinel cause: %v", err)
+	}
+}