The map_confidence_source function was already implemented in
crates/pdftract-core/src/confidence.rs with comprehensive tests.
All acceptance criteria PASS:
- Unit tests for all 12 (UnicodeSource, corrected) combinations
- ToUnicode + corrected=true correctly downgrades to Heuristic
- Ocr is unaffected by correction flag
- Exhaustive match enforces compiler completeness
- INV-9 mapping table documented
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
