docs: preserve synchronized fixture documentation

Author: rlippmann

tests/fixtures/conformance/mutation-isolation/README.md

@@ -94,5 +94,10 @@ now.
 These fixtures cover only the shared API surface for Python and the
 unsynchronized TypeScript port.
 
-They intentionally do **not** include implementation-mechanism requirements
-such as `deepcopy`, frozen objects, or `readonly`.
+They intentionally do **not** include:
+
+* checkpoint APIs
+* removed continuation-state APIs
+* obsolete TypeScript-only authority surfaces
+* implementation-mechanism requirements such as `deepcopy`, frozen objects, or
+  `readonly`