changegroup: use a copy of hookargs when invoking the changegroup hook addchangegroup creates a runhook function that is used to invoke the changegroup and incoming hooks, but at the time the function is called, the contents of hookargs associated with the transaction may have been modified externally. For instance, bundle2 code affects it with obsolescence markers and bookmarks info. It also creates problems when a single transaction is used with multiple changegroups added (as per an upcoming change), whereby the contents of hookargs are that of after adding a latter changegroup when invoking the hook for the first changegroup.