test(lang_contract): assert MEMBER_OF reverse edge (§4c bidirectional coverage)

contract_edge_defines_method asserted only the forward DEFINES_METHOD
(Class->Method) edge. The fork's reverse MEMBER_OF (Method->Class) edge —
emitted in pass_definitions.c:322 / pass_parallel.c / pass_normalize.c and
consumed by pagerank.c (member_rank_factor) — had ZERO test coverage
anywhere in the suite. Add the MEMBER_OF assertion so the function<->class
tie is locked in in both directions.

§4c investigation finding (evidence-based, refutes the plan's assumption
that a code fix was needed): the function<->class tie was ALREADY
implemented, not a merge regression. The Method-only gate
(pass_definitions.c:318) is identical in fork (3018b22:270), upstream
(34efbc0:315), and HEAD; DEFINES_METHOD is tested+passing across 9
languages (defines_method_go/rust/java/csharp/php/ruby/kotlin/ts/scala in
test_edge_types_probe.c); the documented "Go parent_class never derived"
bug is already fixed (extract_defs.c:2776-2783); and every class-scoped
callable is labeled Method with parent_class populated (push_method_def /
generic extractor / extract_rust_impl), so there is no class-scoped
Function gap to fix. Broadening the gate would change nothing. The only
real gap was the untested reverse edge, closed here.

Gate: 5981 passed / 2 failed (the 2 are the deferred B1 incremental
store-layer failures, unrelated to §4c).

Signed-off-by: Andrew Hundt <ATHundt@gmail.com>

tests/test_lang_contract.c

@@ -907,13 +907,18 @@ TEST(contract_edge_defines) {
     PASS();
 }
 
-/* DEFINES_METHOD — Class -> Method when the method's parent_class resolves. */
+/* DEFINES_METHOD — Class -> Method when the method's parent_class resolves.
+ * MEMBER_OF — the reverse Method -> Class edge (fork addition; consumed by
+ * pagerank.c member_rank_factor). Asserting BOTH directions locks in the
+ * function<->class tie (§4c): a class-scoped callable must link to its class
+ * both ways. The reverse edge previously had no test coverage anywhere. */
 TEST(contract_edge_defines_method) {
     static const LangFile f[] = {{"greeter.py",
                                   "class Greeter:\n    def hello(self):\n        return \"hi\"\n\n"
                                   "    def bye(self):\n        return \"bye\"\n\n\n"
                                   "def main():\n    g = Greeter()\n    return g.hello()\n"}};
-    ASSERT_TRUE(edge_present(f, 1, "DEFINES_METHOD", 1)); /* Greeter.hello, Greeter.bye */
+    ASSERT_TRUE(edge_present(f, 1, "DEFINES_METHOD", 1)); /* Class -> Method: Greeter.hello, Greeter.bye */
+    ASSERT_TRUE(edge_present(f, 1, "MEMBER_OF", 1));      /* Method -> Class: reverse edge feeding PageRank */
     PASS();
 }