The hybrid xref handler (merge_hybrid) was already implemented. This adds
a property-based test to verify it handles random combinations of traditional
and stream entries without panicking.
Changes:
- Added proptest_merge_hybrid_no_panic to proptest_tests module
- Tests random entry sets using prop::collection::hash_map
- Covers all entry types (InUse, Free, Compressed)
- Verification note confirms all acceptance criteria PASS
Test results: 9/9 merge_hybrid tests pass
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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