G59 -- The checkpoint is written to be replayed

The in-phase checkpoint block is self-sufficient and verbose — paths, commands, hashes, the exact next step — and is replayed verbatim into the next session, never summarised. A session-close "clean" quotes the fleet's green count; tree-clean and fleet-green are different invariants. provenance: BFM R64 + R58; a fresh session that read a compressed hand-off as "done"