Cliente Server-Sent Events C++ reusable (fn_sse::Client) con background
thread, exponential backoff, Last-Event-ID y stop() que no bloquea.
Implementacion clave: fork+execvp curl directamente (sin /bin/sh wrapper)
para tener el PID real del proceso curl en curl_pid_, lo que permite que
stop() → kill(SIGTERM) → fgets NULL → join() funcione sin bloqueo.
4 tests (Catch2): connect_and_receive_3_events, parse_event_field,
reconnect_on_disconnect, stop_kills_thread. Fixture Python SSE con
/health probe via http_request_cpp_core.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
