We should implement support for discarding pages in PALM, so that we can test the corresponding functionality locally. The implementation should write a tombstone record to PALM in a similar manner to the full image write, so that the page is accessible before the tombstone, but not accessible after it. Reading a discarded page should result in an error.

The implementation should not actually delete any records from the underlying page database, as the discarded page needs to remain accessible to previous checkpoints.