Accrues consumption from a monotonically increasing cumulative counter, tolerating counter resets (the counter's source was destroyed and recreated, restarting from zero — e.g. a VM's cgroup across a restart).

• observe/2 folds in a cumulative reading: the first reading is a baseline; a reading >= the previous adds the delta; a reading below the previous is a reset, and the whole new reading is consumption accrued since recreation.
• total/1 reads the accrued consumption; flush/1 zeroes it (call after the total has been durably recorded) while keeping the baseline.

Works on any Unit.Quantity. Laws under test: a monotone sequence accrues exactly last - first; the total is never negative; observing the same reading twice adds nothing; interleaved flushes conserve the grand total.