Run Seafile v12 reliably on a custom port without bypassing caddy

Seafile Server Docker
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Running on a port other than default http not only has merit of its own but also should be the very basic configuration option. What if I would like to use it for other purposes? There are other servers that use :80 by default, to test them I usually start by running them in completely stock configuration and then making my own changes along the way.

Speaking of which I setup a temporary default Seafile v12 installation and I am finally able to upload and download files, but Seadoc refuses to work. Visiting <IP Address>/sdoc-server returns 404, I had to copy a piece of config from this post by TechnicallyReal to get /sdoc-server to respond with “Welcome to sdoc-server. The current version is 1.0.5“. Which is weird since why on earth would nginx in seafile container have to respond to /sdoc-server requests when everything should go through caddy container and caddy is set up to forward /sdoc-server to whatever IP happens to be assigned to seadoc:

[root@seafile-caddy] / # cat /config/caddy/Caddyfile.autosave:
http://192.168.1.8 {
        @ws {
                header Connection *Upgrade*
                header Upgrade websocket
        }
        reverse_proxy @ws 10.89.0.137:80
        handle_path /socket.io/* {
                rewrite * /socket.io{uri}
                reverse_proxy 10.89.0.137:80
        }
        handle_path /sdoc-server/* {
                rewrite * {uri}
                reverse_proxy 10.89.0.137:80
        }
        reverse_proxy 10.89.0.138:80
}

where 10.89.9.137 is assigned to seadoc:

root@seadoc:/opt/sdoc-server# hostname -i
10.89.0.137

Anyway, trying to open and .sdoc document returns “Load doc content error“ after 504 timeout.