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

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 {