Take an incremental backup: copy only heap pages whose page LSN is greater
than base.source_lsn, plus every changed non-heap file. B+tree .idx
and .eidx files are opaque whole-file artifacts and are never interpreted
as heap pages. Builds on base (a full backup or a prior increment’s
effective state).
Rebuild a data dir from a full base backup plus an ordered chain of
increments. Verifies chain continuity (each increment’s base_source_lsn
must equal the running high-water LSN) and blake3-checks every file/delta,
then validates the result by reopening the catalog.