PasswordPromptCallback typedef
Answers a detected password ask on behalf of the host UI (the TUI's
masked prompt zone, the Flutter sheet). promptLine is the actual
prompt as it appeared in the output ([sudo] password for user:).
Returns the secret to write to the process's stdin, or null to
decline — the harness then writes a bare newline so the command fails
naturally and the user keeps control.
Implementation
typedef PasswordPromptCallback = FutureOr<String?> Function(String promptLine);