The post-prompt settle loop in _handshake had no deadline, so a target that
never falls quiet — a board stuck in a reset loop, whose UART-reset garbage
carries a stray prompt byte — spun the tool forever. Bound it by the handshake
deadline; a real loader still settles on its first quiet read. Regression:
test/test_handshake.py (flood terminates, valid loader still connects).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
