The first half of the flag substrate (DESIGN-flag-vocabularies.md): the shared
format file now defines VERSION_V4, whose index entry is `key | flags(u16) |
value_off | value_len`, and WAL version 2, whose entry carries the same mask
before its length. The mask is a raw u16 — its bits are a vocabulary's business,
never the format's.
Backward compatible, and pinned as such: a v3 index entry and a v1 log entry read
as a zero mask ("no class"), which a scan treats as matching nothing, so a store
folded before the flag existed degrades to "unclassified" rather than "matches
everything". `V3::decode` accepts both versions and `index_stride()` names the
one that differs; `wal_entry` keys its stride off the log's own version byte.
The readers and writers that actually move bytes (the driver's serialize and
append, and `cube-store-raw`) are separate and are the next commit; this is the
shared definition and the arithmetic a reader derives from it.
surface-camera-build
a111d7e8b2