fix: return command output for ssh device and avoid printing null in sequence execution

internal/configuration/sequence.go

@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"os"
 	"regexp"
+	"strings"
 	"time"
 
 	"gopkg.in/yaml.v3"
@@ -127,10 +128,30 @@ func (sm *SequenceMap) executeSequenceSteps(executor CommandExecutor, seqName st
 			return fmt.Errorf("sequence '%s' failed at step %d: %w", seqName, idx+1, err)
 		}
 		// TODO: provide option to suppress output
-		tui.SetOutputColor(tui.CBlue, os.Stdout)
-		enc := yaml.NewEncoder(os.Stdout)
-		enc.Encode(res)
-		tui.ResetOutputColor(os.Stdout)
+		if res != nil {
+			tui.SetOutputColor(tui.CBlue, os.Stdout)
+			switch v := res.(type) {
+			case string:
+				if len(strings.TrimSpace(v)) > 0 {
+					if !strings.HasSuffix(v, "\n") {
+						v += "\n"
+					}
+					fmt.Print(v)
+				}
+			case fmt.Stringer:
+				s := v.String()
+				if len(strings.TrimSpace(s)) > 0 {
+					if !strings.HasSuffix(s, "\n") {
+						s += "\n"
+					}
+					fmt.Print(s)
+				}
+			default:
+				enc := yaml.NewEncoder(os.Stdout)
+				enc.Encode(res)
+			}
+			tui.ResetOutputColor(os.Stdout)
+		}
 	}
 	return nil
 }

internal/configuration/sequence_test.go

@@ -418,3 +418,25 @@ func TestExecute_DefaultTimeout_UsedWhenUnset(t *testing.T) {
 		t.Fatalf("unexpected error: %v", err)
 	}
 }
+
+// TestExecute_CommandOutputFormatting verifies that string command output is handled
+// and that steps returning nil do not print "null".
+func TestExecute_CommandOutputFormatting(t *testing.T) {
+	cmd1 := configuration.SequenceCmd{Cmd: configuration.T("cmd1")}
+	cmd2 := configuration.SequenceCmd{Cmd: configuration.T("cmd2")}
+	sm := configuration.SequenceMap{"seq": {cmd1, cmd2}}
+
+	exec := &mockExecutor{
+		executeFunc: func(callIdx int, _ context.Context, _ *configuration.SequenceCmd) (any, error) {
+			if callIdx == 0 {
+				return "expected command output\n", nil
+			}
+			return nil, nil
+		},
+	}
+
+	if err := sm.Execute(exec, "seq"); err != nil {
+		t.Fatalf("unexpected error executing sequence: %v", err)
+	}
+}
+

internal/device/ssh/sshdevice.go

@@ -135,10 +135,11 @@ func (d *SSHDevice) executeCommandString(ctx context.Context, cmd string) (any,
 	case err := <-done:
 		var exitError *stdssh.ExitError
 		if errors.As(err, &exitError) {
-			return output, fmt.Errorf("exit code (%d)", exitError.ExitStatus())
-		} else {
+			return output.String(), fmt.Errorf("exit code (%d)", exitError.ExitStatus())
+		} else if err != nil {
 			return nil, err
 		}
+		return output.String(), nil
 
 	case <-ctx.Done():
 		_ = session.Signal(ssh.SIGKILL)

internal/device/ssh/sshdevice_test.go

@@ -261,13 +261,17 @@ func TestSSHDevice_ExecuteCommand_OutputCaptured(t *testing.T) {
 	defer dev.Close()
 
 	cmd := mustSequenceCmd(t, "cmd: echo-test")
-	if _, err := dev.ExecuteCommand(context.Background(), cmd); err != nil {
+	res, err := dev.ExecuteCommand(context.Background(), cmd)
+	if err != nil {
 		t.Fatalf("unexpected error executing command: %v", err)
 	}
 
 	if !strings.Contains(logBuf.String(), want) {
 		t.Errorf("log writer: expected to contain %q, got %q", want, logBuf.String())
 	}
+	if outStr, ok := res.(string); !ok || !strings.Contains(outStr, want) {
+		t.Errorf("ExecuteCommand result: expected string containing %q, got %v", want, res)
+	}
 }
 
 // TestSSHDevice_ExecuteCommand_ParamsConcatenated verifies that the Cmd field