Storage Format

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

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

The header contains:

• metadata.format_version
• 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, then the JSON header, then the listed Tantivy files by positional reads. The current reader loads listed files into Tantivy RamDirectory; a future reader can replace this with a custom seek-on-demand Directory without changing the envelope.