bumped whenever the record shape changes; the precompiled image carries it, and it is part of
the key an image is cached under, so a bump invalidates every stored image.
It is bumped for a change in what the records contain as well as for a change in their shape:
when the reader learns to read something it used to drop -- a DateTime value, say -- every image
built before is still valid schema-N and still parses, but it is less faithful than the file it
was built from, and nothing else would ever invalidate it. The source digest cannot: the source
did not change. This number is the only lever.
bumped whenever the record shape changes; the precompiled image carries it, and it is part of the key an image is cached under, so a bump invalidates every stored image.
It is bumped for a change in what the records contain as well as for a change in their shape: when the reader learns to read something it used to drop -- a DateTime value, say -- every image built before is still valid schema-N and still parses, but it is less faithful than the file it was built from, and nothing else would ever invalidate it. The source digest cannot: the source did not change. This number is the only lever.