What the platform running Managoat.Runner supplies: a way to reach a runner's connection process by id, and two notifications it may act on.

The connection process and the adapter need exactly these things from their host, and none of them is protocol:

• register/2 — when a socket opens, register the calling process (the connection) under the runner id, with meta. A second connection for the same id is refused with {:error, :already_registered}, and the connection closes it with code 4409.
• unregister/1 — when the socket closes, from the connection process, before presence/3 fires so a subscriber that looks the runner up on receipt sees the truth.
• whereis/1 — the connection process for a runner id, from any node, or nil. Managoat.Runner.Connection.call/3 and unsubscribe/3 route through it.
• online/0 — every runner id currently registered, with its meta. Managoat.Runner.Adapter.list_all_names/0 walks them.
• heartbeat/1 — the runner is alive; sent every 20 seconds while the socket is up. A host that keeps a last_seen_at stamps it here.
• presence/3 — the runner went :online (registered) or :offline (unregistered), with the meta it registered with. A host with a roster to refresh broadcasts it here.

meta is an opaque map: the host puts what it needs in it when the connection is opened (the WebSock init map's :meta key) and gets it back on online/0 and presence/3. The library never reads a key from it.

A host may send {:runner_deleted, runner_id} to the connection process (found through whereis/1); the connection closes the socket with code

4404. That message is part of the contract between host and connection.

Managoat.Runner.Host.Local is the reference implementation over a plain Registry, with the two notifications as no-ops. The library's own tests run against it, and so does a consumer without a cluster.