Implement the Receipt struct and lite-mode JSON serialization for
visual citation receipts. This provides cryptographic proof of
provenance for extracted text.
Changes:
- Add Receipt struct with 6 fields (pdf_fingerprint, page_index,
bbox, content_hash, extraction_version, svg_clip)
- Implement Receipt::lite() constructor with NFC normalization
- Integrate Receipt into SpanJson and BlockJson schemas
- Add unicode-normalization and serde_json dependencies
Acceptance criteria:
- Receipt::lite() produces valid receipts with svg_clip=None
- Lite mode JSON omits svg_clip key via skip_serializing_if
- Content hash uses NFC normalization for cross-platform stability
- Receipt wired into SpanJson and BlockJson types
Note: 100 receipts aggregate size is ~27 KB (not 15 KB as planned).
The 15 KB target is not achievable with required field sizes.
Refs: pdftract-5zm86, Phase 6.8 Visual Citation Receipts (lines 2351-2417)
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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