A sidecar already gets a port and nothing here changes that: it binds 0, the
kernel picks, it announces the number. That is right for what it is - a private
detail between two processes, loopback, re-chosen every restart, and nothing
outside Officer needs it.
A port something ELSE connects to is a different thing. A plugin serving a
website has to be reachable from nginx, which means the number must survive a
restart and be knowable by whoever writes the proxy configuration. Ephemeral
fails both, which is why the first site plugin was going to hardcode 3011 and
hope.
So: `extraPorts: [{ name: 'site', preferred: 3011 }]` in a manifest, allocated at
install, persisted in plugin_ports, and delivered as PORT_SITE in the sidecar's
pm2 environment. Environment rather than the registration socket because a socket
answer arrives after the process has already had to decide what to bind, and pm2
is the only thing that can tell a process something before it starts.
What the platform guarantees is the part per-plugin config could never do: no two
plugins are ever handed the same number. That is a unique index rather than a
convention, because a collision is not a duplicate row - it is two services
fighting over a listener where the loser fails to bind and the winner is whoever
started first.
`preferred` is a wish, not a claim. A plugin usually arrives after the thing that
connects to it, and moving that configuration is work the platform can spare
somebody; but a preference that could fail an install would be a claim wearing a
softer word.
Allocations survive uninstall and are released only by purge. The number is
written down where this database cannot see it, so handing it to a different
plugin because this one was briefly removed points that configuration at the
wrong service.
Pm2App gained `env`, emitted as JSON rather than hand-quoted: a port is a number
today, but this is the seam where a path arrives eventually, and one apostrophe
in a value produces a file PM2 cannot parse - which takes every process on the
machine down, not just the plugin's.
Verified: stable across calls, distinct across plugins, released cleanly,
honours a preference, and a plugin declaring no ports gets no env key at all.