This is something I considered, however, I didn't add it due to the consideration that UDP protocols like WireGuard already have PersistentKeepalive which would keep the connections open, so I did not found TCP keepalive that important to add in the short term.

Yup,wg has the keepalive setting,but other udp tunnels not have one.Just follow ur priority.Thx

I think let those udp tunnels that don't support keepalive join the heartbeat feature to be right.

I think keep-alive is needed. If keep-alive packet is not received in-time, we must treat connection as broken, and re-establish TCP connection. WireGuard PersistentKeepalive cannot achieve this.

Yup,wg has the keepalive setting,but other udp tunnels not have one.Just follow ur priority.Thx

Your issue can be temporarily addressed by setting a cron job which pings your server using nmap UDP scan.