parity harness, pinned to the python tokeniser over 10k lines

parity/KNOWN.md

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+# Known divergences
+
+Places where the Rust and the Python deliberately do not agree, each with the
+reason it is acceptable. A divergence that is not written down here is a bug,
+and loosening a test instead of adding an entry here is how a port rots.
+
+Format:
+
+```
+## <function> — <one-line summary>
+
+**Python:** what it does.
+**Rust:** what it does instead.
+**Why this is acceptable:** the argument, including what input class is
+affected and how often it occurs in practice.
+**Measured:** how many records out of how many differ.
+```
+
+---
+
+None recorded yet.