Push an Astro site and Deplo builds it and serves it on port 4321, on a server you own, with HTTPS in front.
Detection runs on every deploy and is never stored, so a change to the project is picked up by the next push.
Short answers to what comes up before moving a Astro app onto your own server.
Add the @astrojs/node adapter in standalone mode: the build then has a server that Deplo starts on the app's port.
In the app's settings, per environment. They are available during the build too, and secret values are write only: nothing reads them back.
Commands you type in the app's settings always win over detection, and a Dockerfile build takes over entirely.
Answer three questions and pick a host, or install Deplo on a server you already have. It's free, and leaving is as easy as arriving. What you do with the money you save is your business.