wal::reader is the table of layouts an image reads, and layout::check hands back the reader for a stamp it knows. The first boot under a moved stamp takes a checkpoint in today's shape, trims the log and restamps, so an upgrade inside the window costs a restart rather than the accounts. The window is N-1, every row has a data directory under tests/fixtures/layout/, and tests/layouts.rs opens each one and answers its expected.json. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Change-Id: I7dc42d7fedf9b7c067c91cd3e178be4b081e48d2