[pitboss] phase 16: Track B — Rust + C + C++ harness emitter shapes

tests/dynamic_fixtures/cpp/free_fn/benign.cpp

@@ -0,0 +1,12 @@
+// Phase 16 — free function with (const char *, size_t), benign.
+
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
+
+void run(const char *payload, std::size_t len) {
+    (void)payload; (void)len;
+    std::printf("__NYX_SINK_HIT__\n");
+    std::fflush(stdout);
+    std::system("echo hello");
+}