pub const JOURNAL_TOMBSTONE: u64 = u64::MAX; // 18_446_744_073_709_551_615u64Expand description
The blob_size of a journal row that is not a pack: a tombstone,
whose blob_offset names a pack this archive has retired.
u64::MAX rather than 0, and that is the whole of the encoding decision.
The journal’s schema is two u64s and a third column cannot be added without
making every existing journal file unreadable by the writer that appends to
it, so the marker has to live inside a value that no real pack can take. A
zero-length append is at least conceivable — a caller handing append an
empty slice gets (cursor, 0) — while an extent of 2^64-1 bytes cannot
exist on any filesystem this will ever run on. The unreachable value is the
safe one.