Development record

`03-embark.md:141` says verification refuses a symlink or an oversize file anywhere inside the lifeboat. The size cap applies only to files the manifest hashes (`internal/core/lifeboat/embark.go:218`): an 18 MiB `review/big.bin` in the excluded layer passes `abcd embark probe` with exit 0, while a symlink there and an oversize hashed file are refused. The comment at `internal/core/lifeboat/embark.go:184` carries the same wording.