add: if (am_generator && msg_fd_in >= 0) contiguous_write_len = 0;
context: static void mplex_write(enum msgcode code, char *buf, size_t len){	char buffer[4096];	size_t n = len;	SIVAL(buffer, 0, ((MPLEX_BASE + (int)code)<<24) + len);	if (n > sizeof buffer - 4)		n = sizeof buffer - 4;	memcpy(&buffer[4], buf, n);	writefd_unbuffered(sock_f_out, buffer, n+4);	len -= n;	buf += n;	if (len)		writefd_unbuffered(sock_f_out, buf, len);}