Widen the exception guard from OSError to Exception (re-raising
KeyboardInterrupt/EOFError first) so any prompt_toolkit runtime
failure degrades to input() — matching the established pattern in
masked_secret_prompt. ValueError and RuntimeError can arise from
exotic stream wrappers or event-loop issues with the same root cause:
prompt_toolkit cannot attach stdin on the terminal.
Add test_line_input_falls_back_to_input_on_any_prompt_toolkit_failure
covering the ValueError case.
45aa0dc33e