Docs in subscribed queries are always considered to be subscribed

At the moment, when you create a subscribe query, the query will automatically pass all ops back to the client, regardless of whether it wants to be subscribed or not. This can be quite confusing:

• a Doc that matches a subscribe query will receive 'op' events, even though doc.subscribed === false
• calling doc.unsubscribe() will not actually stop the doc receiving 'op' events

It's possible to make this behaviour a bit more consistent in a few ways:

• check at the server if the client doc is subscribed, and only send ops back in that case
• make connection.get() return new instances of docs rather than cached instances (which I've personally always expected) — this would allow individual Doc instances to be unsubscribed, while query.results stay subscribed

At the very least it might be nice to error in doc.unsubscribe() if the doc matches a query (and therefore cannot be unsubscribed). It may also be nice to change doc.subscribed into a method/getter which checks if it's part of a query, to reflect its "true" state

All of the above changes would technically be breaking.

One nice, non-breaking thing we could potentially do is to just logger.warn() if unsubscribing a doc that matches a query.

Start with lib/query-emitter.js at the linked operation handling, then trace connection.get(), doc.unsubscribe(), and doc.subscribed for cached documents matched by queries. The issue lists several breaking and non-breaking options, so first confirm the intended behavior with maintainers; done requires an agreed subscription model and corresponding behavior for operations and unsubscribe().