Extract the ssh debug commands into a transport neutral commands package (#1958)

Migrate commands from ssh into a transport neutral package

 - add golden tests validating that output remains unchanged
 - move commands to commands.go

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

ssh_commands_test.go

@@ -0,0 +1,57 @@
+package nebula
+
+import (
+	"bytes"
+	"fmt"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/slackhq/nebula/commands"
+	"github.com/slackhq/nebula/config"
+	"github.com/slackhq/nebula/test"
+)
+
+// TestSSHCommandSurface is a characterization test for the ssh command surface.
+// It pins the registered command set, their descriptions, help text and flag definitions
+// so that moving the registry to a transport neutral package is provably a relocation
+// rather than a rewrite. Regenerate with `go test . -run TestSSHCommandSurface -update`.
+func TestSSHCommandSurface(t *testing.T) {
+	got := renderCommandSurface(registeredCommands(t).All())
+	test.Golden(t, filepath.Join("testdata", "ssh_commands.golden"), got)
+}
+
+// registeredCommands returns a registry holding every command nebula serves. The
+// Interface is never dereferenced: attachCommands only closes over it.
+func registeredCommands(t *testing.T) *commands.Registry {
+	t.Helper()
+	l := test.NewLogger()
+	reg := commands.New()
+	attachCommands(l, config.NewC(l), reg, &Interface{})
+	return reg
+}
+
+func renderCommandSurface(cmds []*commands.Command) string {
+	lines := make([]string, 0, len(cmds))
+	for _, cmd := range cmds {
+		b := &bytes.Buffer{}
+		fmt.Fprintf(b, "%s\n", cmd.Name)
+		fmt.Fprintf(b, "  short: %s\n", cmd.ShortDescription)
+		fmt.Fprintf(b, "  help: %s\n", cmd.Help)
+
+		if cmd.Flags != nil {
+			fl, _ := cmd.Flags()
+			if fl != nil {
+				fb := &bytes.Buffer{}
+				fl.SetOutput(fb)
+				fl.PrintDefaults()
+				fmt.Fprintf(b, "  flags:\n%s", fb.String())
+			}
+		}
+
+		lines = append(lines, b.String())
+	}
+
+	// In the order All gives, so the golden pins display order too.
+	return strings.Join(lines, "")
+}