Pull the #33271 post-interrupt recovery (flush_stdin + _force_full_redraw)
out of process_loop's finally block into _recover_terminal_after_interrupt(),
and replace the inline-logic-copy tests with ones that exercise the real
helper plus a source guard that process_loop still invokes it behind the
_last_turn_interrupted gate.
When the agent is interrupted during processing, prompt_toolkit's
renderer and VT100 input parser can be left in an inconsistent state.
CSI 6n cursor position report responses leak as literal text
(^[[19;1R) and the terminal stops accepting keyboard input.
Fix: in process_loop's finally block, after an interrupted turn:
- flush_stdin() to drain stray escape bytes from the OS input buffer
- _force_full_redraw() to reset prompt_toolkit's renderer cache
Closes#33271
