When caps node was requested, disco infos was returned from cache + infos from normal
disco gathering, resulting in doubled items and other entities rejecting the disco info.
This is fixed by subclassing the disco handler to add a trigger. This trigger is used by
XEP-0115 to short circuit the disco gathering and returned its cached data instead.
Our own hash is re-generated on each connection, and validated, so if there is a bug, this
helps see and catch it.
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