docs/storage-format.md

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# Storage Format

Version 1 uses a front-loaded self-describing envelope:

```text
magic:      8 bytes  "PFTIDX01"
version:    u32      1
header_len: u32
header:     JSON metadata and archive directory
body:       concatenated Tantivy files
```

The header contains:

- `metadata.config`
- `metadata.document_count`
- `metadata.tantivy_version`
- `files[]`: Tantivy file name, body-relative offset, and length

Readers first read the 16-byte fixed prefix and JSON header. The Rust reader
then exposes listed Tantivy files through a read-only seek-on-demand directory,
so segment file bytes are fetched by positional reads only when Tantivy asks for
the corresponding byte range. Readers reject headers larger than 16 MiB before
allocating the header buffer.

The body stores Tantivy segment files directly. Readers reject index files whose
recorded `metadata.tantivy_version` does not match the linked Tantivy runtime.