The conformance test rig at crates/pdftract-core/tests/conformance.rs
already exists and is comprehensive. Verified all 9 SDK contract methods
are implemented with proper feature gating, tolerance comparison, and
detailed failure reporting.
Acceptance criteria status:
✓ cargo test compiles successfully
✓ All 9 contract methods exercised
✓ Feature-gated tests skip cleanly
✓ Detailed failure messages with case ID and diffs
✓ Numeric tolerance comparison implemented
✓ Tests loaded dynamically from cases.json
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