Recovers CD sector prefix/suffix arenas in a v2 image whose resumed dump
sessions left the final deduplication table referencing slots past the
shrunken data block. Scans the file for every prefix/suffix generation,
rebuilds a fresh compact arena and DDT2 for the final table by sourcing
each custom slot from the generation that held it, and rewrites the index.
Supports --dry-run to report recoverable/lost slots without writing.