verify that history from a previous version of the channel is always unavailable

[slingamn]

Edge case I just thought of. Suppose persistent history is enabled, and also history.persistent.unregistered-channels is enabled (not a default). Unregistered channels are removed from the server when they have no members. In this case, if someone recreates the channel by rejoining, they shouldn't be able to see prior history from the persistent database even if they have chanops.

[slingamn]

Confirmed that this issue exists in 2.10.

[slingamn]

I looked into fixing this. Basically, we need to impose a cutoff corresponding to the time the current iteration of the channel was created (we already have cutoff support). The problem is that we do not track the creation time, as opposed to the registration time, of registered channels.

Since this implementation would leave the previous history lines in an unviewable but potentially unreclaimable state, we should also consider adding support for deleting them automatically.