Since you're already using Tasker, you could use it to launch Tailscale on the phone at boot - I've got mine set to do this so my phone reconnects to tailscale after a reboot.

Now I have another mobile with more control, so restart is not a problem anymore, and as I can SSH in to it using Termux. This basically handles all of my needs.

Now I just need to get enough momentum to set up the process of waking up my desktop as needed and set up radical caldav server in the mobile.