Add safe immutable directory promotion

internal/fileops/directory_special_unix_test.go

@@ -0,0 +1,35 @@
+//go:build !windows
+
+package fileops
+
+import (
+	"os"
+	"path/filepath"
+	"syscall"
+	"testing"
+)
+
+func TestPromoteDirectoryRejectsNamedPipe(t *testing.T) {
+	root := t.TempDir()
+	src := filepath.Join(root, "source")
+	dst := filepath.Join(root, "destination")
+	if err := os.Mkdir(src, 0o755); err != nil {
+		t.Fatalf("Mkdir(source) error = %v", err)
+	}
+	pipe := filepath.Join(src, "events.pipe")
+	if err := syscall.Mkfifo(pipe, 0o600); err != nil {
+		t.Skipf("Mkfifo() unavailable: %v", err)
+	}
+
+	if err := PromoteDirectory(src, dst); err == nil {
+		t.Fatal("PromoteDirectory() error = nil, want named pipe rejection")
+	}
+	info, err := os.Lstat(pipe)
+	if err != nil || info.Mode()&os.ModeNamedPipe == 0 {
+		t.Fatalf("source named pipe was not preserved: info=%v err=%v", info, err)
+	}
+	if _, err := os.Lstat(dst); !os.IsNotExist(err) {
+		t.Fatalf("Lstat(destination) error = %v, want not exist", err)
+	}
+	assertNoMatchingTempDirectories(t, root, ".destination.tmp-")
+}