Add durable NUnit parity harness

README.md

@@ -32,6 +32,13 @@ cargo build --workspace
 cargo test --workspace --no-run
 python3 tools/generate_rust_mapping.py --check
 python3 tools/generate_api_shims.py --check
+python3 tools/check_test_parity.py
 ```
 
+`tests/upstream-tests.json` is the machine-readable NUnit parity catalog.
+Translated tests live in hand-written Rust files with the `parity-case` marker
+documented in `tests/PARITY.md`; `python3 tools/generate_surface.py --check`
+verifies the catalog against the pinned adjacent LibreMetaverse checkout without
+overwriting those files.
+
 Running `cargo test --workspace` is intentionally red during the shim stage.