Without SO_KEEPALIVE a silently-dropped client (SSH tunnel reset, laptop
sleep, NAT timeout) leaves the TCP leg half-open forever: receive_text()
blocks indefinitely and the disconnect teardown (detach, orphan reap,
resume replay) never runs. The server then leaks the session and never
reclaims its orphans.
_disable_nagle already reaches the raw socket, so enable keepalive there:
SO_KEEPALIVE on, plus TCP_KEEPIDLE=30s / TCP_KEEPINTVL=10s /
TCP_KEEPCNT=3 on Linux and TCP_KEEPALIVE=30s on macOS. A dead peer is now
detected in ~60s instead of never. Best-effort like the Nagle tuning —
any failure to reach the socket is logged at debug and skipped.
Tests: new tests/tui_gateway/test_ws_keepalive.py fakes the socket and
pins SO_KEEPALIVE + the platform-specific idle tuning, plus the
no-transport no-raise path. tests/tui_gateway: 336 passed.
Christian Pompa
d6bc3f2bca