All 7 sub-components implemented:
- Traditional xref table parser
- Xref stream parser (PDF 1.5+)
- Hybrid file merger
- Forward scan fallback
- Incremental update chain handler
- Linearized PDF support
- Comprehensive test corpus (90 tests pass)
Acceptance criteria met:
- All Critical tests from plan Section 1.3 pass
- INV-8 maintained (no panic, verified by proptests)
- Module at crates/pdftract-core/src/parser/xref.rs
- Test fixtures for linearized, multipage, and minimal PDFs
