The cutter materialized every interior cut up front, so a tiny sidecar
declaring one enormous extent could allocate gigabytes of cut offsets
before any media byte arrived. Keep only the extent start offsets,
bounded by the extent count, and derive each cut arithmetically.
A format adapter reduces one container format to three things the core
understands: extent sizes, an alignment quantum, and an opaque payload.
Capabilities beyond identity (Indexer, SidecarIndexer, Viewer) are
discovered by type assertion. The layout persists in one compact
extended attribute keyed by extent sizes rather than chunk ids, so it
survives chunk manifest folding, and the Cutter turns it into upload
chunk boundaries clamped by maxMB and the align quantum. The formattest
kit holds every adapter to no-panic parsing of truncated input.
Chris Lu