Tie nREPL sessions together in the HUB

[jonpither]

The idea is that if a dev has 2 nREPL sessions open, the data from each is combined to present a consistent view of what the user is doing?

I had thought this feature is a prerequisite for CIDER-SPY to be useful, but now I think it can be bumped to a future version.

WRT to implementation details, we need to tie the nREPL sessions together somehow.

We could just use alias coming from CIDER-SPY mode if present, but I've a feeling this is a bit weak. If could though be a simple first step. If we do choose alias, we may want to consider moving the alias config out of the CIDER-SPY layer and make it accessible to the middleware directly via some config (perhaps using ENVIRON).

Another option is to use an overarching ID generated by CIDER-SPY. The downside again with any CIDER-SPY option is that users sessions are being synced up at the CIDER-SPY level. The users need CIDER-SPY in place to make syncing work.

[jonpither]

We don't need to "tie the nREPL sessions together somehow". Keep them separate, ensure aliases are all unique. Use session IDs where possible, although messages can still resolve to aliases rather than session IDs so that they are long lived.