cli: do not use interactive TUI elements when control terminal (tty) is not available (fixes #386)

internal/cli/connect.go

@@ -31,10 +31,9 @@ func ConnectCluster(ctx context.Context, conn config.MachineConnection, opts Con
 }
 
 // connectClusterWithProgress connects to the cluster while displaying a progress spinner.
-// If the stdout is not a terminal, it falls back to simple progress logs to stderr.
+// If a terminal is not available, it falls back to simple progress logs to stderr.
 func connectClusterWithProgress(ctx context.Context, conn config.MachineConnection) (*client.Client, error) {
-	// If stdout is not a terminal, fall back to simple progress logs.
-	if !tui.IsStdoutTerminal() {
+	if !tui.IsTerminalAvailable() {
 		fmt.Fprintln(os.Stderr, "Connecting to", conn.String())
 		cli, err := connectCluster(ctx, conn)
 		if err != nil {
@@ -45,8 +44,8 @@ func connectClusterWithProgress(ctx context.Context, conn config.MachineConnecti
 		return cli, err
 	}
 
-	// Run the connection TUI model.
-	p := tea.NewProgram(newConnectModel(ctx, conn))
+	// Run the connection TUI model. Render to stderr so stdout stays clean for command output.
+	p := tea.NewProgram(newConnectModel(ctx, conn), tea.WithOutput(os.Stderr))
 	model, err := p.Run()
 	if err != nil {
 		return nil, fmt.Errorf("run connection TUI: %w", err)

internal/cli/machine.go

@@ -99,14 +99,14 @@ func provisionMachine(ctx context.Context, exec sshexec.Executor, version string
 }
 
 func promptResetMachine() error {
-	if !tui.IsStdinTerminal() {
+	if !tui.IsTerminalAvailable() {
 		return errors.New("the remote machine is already initialised as a cluster member; " +
 			"cannot ask to confirm reset in non-interactive mode, " +
 			"use --yes flag or set UNCLOUD_AUTO_CONFIRM=true to auto-confirm")
 	}
 
-	fmt.Println(tui.Red.Render("The remote machine is already initialised as a cluster member. Resetting it will:\n" +
-		"- Remove all service containers from the machine\n" +
+	fmt.Fprintln(os.Stderr, tui.Red.Render("The remote machine is already initialised as a cluster member. Resetting it will:\n"+
+		"- Remove all service containers from the machine\n"+
 		"- Reset the Uncloud daemon on the machine to the uninitialised state"))
 
 	var confirm bool
@@ -119,7 +119,9 @@ func promptResetMachine() error {
 				Value(&confirm),
 		),
 	).WithTheme(tui.ThemeConfirmDanger()).
-		WithAccessible(true)
+		WithAccessible(true).
+		// Render to stderr so stdout stays clean for command output.
+		WithOutput(os.Stderr)
 	if err := form.Run(); err != nil {
 		return fmt.Errorf("prompt user to confirm: %w", err)
 	}

internal/cli/tui/prompt.go

@@ -25,7 +25,9 @@ func Confirm(title string) (bool, error) {
 				Value(&confirmed),
 		),
 	).WithTheme(ThemeConfirm()).
-		WithAccessible(true)
+		WithAccessible(true).
+		// Render to stderr so stdout stays clean for command output.
+		WithOutput(os.Stderr)
 	if err := form.Run(); err != nil {
 		return false, err
 	}
@@ -51,6 +53,14 @@ func ThemeConfirmDanger() huh.Theme {
 	})
 }
 
+// IsTerminalAvailable reports whether the control terminal (TTY) is available so an interactive TUI can run.
+func IsTerminalAvailable() bool {
+	// Bubbletea interactive programs read keyboard input from stdin and render to stdout (default) or stderr (uncloud),
+	// so both must be terminals. In particular, bubbletea falls back to opening /dev/tty when stdin is not a terminal,
+	// which fails when there is no controlling terminal. See https://github.com/psviderski/uncloud/issues/386
+	return IsStdinTerminal() && IsStderrTerminal()
+}
+
 // IsStdinTerminal checks if the standard input is a terminal (TTY).
 func IsStdinTerminal() bool {
 	return term.IsTerminal(int(os.Stdin.Fd()))
@@ -61,6 +71,11 @@ func IsStdoutTerminal() bool {
 	return term.IsTerminal(int(os.Stdout.Fd()))
 }
 
+// IsStderrTerminal checks if the standard error is a terminal (TTY).
+func IsStderrTerminal() bool {
+	return term.IsTerminal(int(os.Stderr.Fd()))
+}
+
 // TerminalWidth returns the width of the terminal.
 // Returns 0 if stdout is not a terminal or the width cannot be determined.
 func TerminalWidth() int {

internal/cli/tui/spinner.go

@@ -0,0 +1,37 @@
+package tui
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"charm.land/huh/v2/spinner"
+	"charm.land/lipgloss/v2"
+)
+
+// RunSpinner shows an animated spinner that prints title while running action.
+// When the terminal (TTY) is not available, it prints the title as plain text.
+// It renders to stderr so stdout stays clean for command output.
+func RunSpinner(ctx context.Context, title string, action func(ctx context.Context) error) error {
+	// Fall back to plain text when a terminal is not available to avoid the bubbletea /dev/tty error and to keep
+	// escape codes out of redirected output.
+	if !IsTerminalAvailable() {
+		fmt.Fprintln(os.Stderr, title)
+		return action(ctx)
+	}
+
+	return spinner.New().
+		// Leading space offsets the title from the spinner glyph.
+		Title(" " + title).
+		Type(spinner.MiniDot).
+		WithTheme(spinner.ThemeFunc(func(isDark bool) *spinner.Styles {
+			return &spinner.Styles{
+				Spinner: lipgloss.NewStyle().Foreground(lipgloss.Yellow),
+				Title:   lipgloss.NewStyle(),
+			}
+		})).
+		WithOutput(os.Stderr).
+		Context(ctx).
+		ActionWithErr(action).
+		Run()
+}