Implement Merkle SHA-256 fingerprint algorithm for PDF structural
fingerprinting as specified in Phase 1.7 of the plan.
Components:
- FingerprintInput struct with page data and catalog flags
- Per-page hashing: content streams (normalized), resources (sorted),
geometry (4dp banker's rounding)
- Structure tree hash for tagged PDFs
- Catalog feature flag byte (encryption, JS, XFA, OCG)
Acceptance criteria:
- INV-3: 100% reproducible fingerprints (test passes)
- INV-13: Output format ^pdftract-v1:[0-9a-f]{64}$ (test passes)
- Performance: 100-page PDF in < 1ms (test passes)
- KU-7: WARN - no linearized fixtures available
Closes pdftract-q15sh
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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