First stage of the co-frozen D1+D3+repacking unit: the format core,
self-contained under _generations/segments/.
- seg-<firstGen,20pad>.bgs: append-once packs of consecutive
generations (magic BGS1; frame = u32 len + u32 crc32c + msgpack
[generation, timestamp, delta, records, flags]; flags reserves
compressed-payload evolution without a format break). Sealed
segments are immutable — fold refuses overlap with sealed ranges.
- seg-<firstGen>.idx: DERIVED sidecar (per-generation frame offsets +
per-id generation postings + checksums); lost/corrupt sidecars
rebuild from their segment loudly; a damaged segment (frame CRC
mismatch) fails loudly, never serves wrong bytes.
- manifest.json: the one discovery path — open() reads it and never
lists the packed backlog (the scan-wedge class's cure); refuses a
newer manifest version rather than serving partial history.
- D3 semantics: dropSegmentsBelow reclaims WHOLE segments at
boundaries only and bumps compactedBelow durably; archival-profile
enforcement stays with the caller per the co-freeze.
- D8 rider: digestThroughPacked(g) — deterministic crc32c chain over
sealed-segment checksums (+ frame-level prefix mid-segment),
O(segments), reopen-stable.
Also fixes a cross-adapter contract bug the suite caught: memory
storage's deleteObjectFromPath ignored the raw-bytes store, so
deleteRawObject on a raw-bytes path (fact-log or segment files)
silently no-op'd — deletes now match filesystem unlink semantics.
Six pins. Wiring into GenerationStore (two-tier reads, the repacker,
cold-open manifest path) lands with the rest of the unit before its
release; cortex's fact-record/stamp shapes reconcile the sidecar
keying when they post.
