Module partial 

Seek-based partial descriptor loading (Phase 11.12, review priority #2).

PartialDescriptor serves exact source byte ranges without reading the whole .voldoc blob. It walks the file’s record framing once, reading only the small records a query needs (UNIVERSE, FORMAT, GRAPH, OBSERVATION_INDEX, INTEGRITY, TRAILER) and seeking over the payloads of every OBJECT/ENTROPY_CHANNEL/MODEL record, remembering their on-disk offsets. When a range is served it reads only the records the selected ops reference, and every payload it materializes is CRC32C-verified.

Requires an observation index

The lazy lane needs an OBSERVATION_INDEX op table to learn each op’s output length without decoding every channel. PartialDescriptor::open returns Ok(None) when the descriptor has no op table, references external objects, or is otherwise ineligible; the caller then falls back to the full crate::container::Descriptor::parse path (recorded honestly as a full descriptor read).

Integrity is honest

A partial read cannot recompute the whole-source SHA-256, and it does not re-hash the blob against its content id; it verifies each record’s CRC32C as the record is read (including every payload it materializes) and cross-checks the op table against the program’s own op shapes. A corrupted unneeded record is not read, so it does not break a narrow observation. The delivered bytes are an observation, never a verified archival read.

Structs

PartialDescriptor

A descriptor opened for seek-based partial reads.

Enums

PartialLoad

The outcome of inspecting a descriptor for lazy serving.