Minor visual issues with history cleaning
If one right clicks in the chat window and selects Clear, and then presses No, then recent conversation still disappears until you reopen that window. Also, probably there is no need for Cancel button.
If one selects to delete History, then History button disappears from the toolbar menu. But after Spark restart if one opens that contact again, History button is showing again, though there is no history to show.
Mass closing of resolved issues
The problem might be that Spark doesnt have such methods for disabling GUI elements and so this should be implemented. Maybe im gateways toolbar technique can bu borrowed for graying out buttons.
I think the best way will be to disable this button is there is no history for opened chat, but show it always.
What about how end user sees that? If he opens a chat window and don't see a history button, maybe he won't remember that he has cleaned all history with that contact and instead think it is a bug? Maybe it is better to have this button showing up (or maybe grayed out if no history there) all the time but showing no history if it is not there. There can be also a text message in the history window e.g. "There are no history saved for this contact".
One way is to create EventListener for chat clear action.