libibus destroys an input context with Destroy on
org.freedesktop.IBus.Service, not on the InputContext interface, so the
call went unanswered and the context slot stayed taken until the whole
connection closed. A long-lived GTK process that opens and closes text
widgets exhausted the 1024 slots and then got LimitsExceeded for every
new field. The live contract test now destroys a context that way and
checks the path is gone.