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

tests/dynamic_fixtures/cpp/main_argv/vuln.cpp

@@ -0,0 +1,18 @@
+// Phase 16 — main(argc, argv), vulnerable.
+//
+// Renamed away from `main` so the harness `main` symbol does not collide.
+// Shape marker: int main(int argc, char *argv[])
+// Cap: CODE_EXEC.
+
+#include <cstdio>
+#include <cstdlib>
+#include <string>
+
+int nyx_entry_main(int argc, char *argv[]) {
+    std::printf("__NYX_SINK_HIT__\n");
+    std::fflush(stdout);
+    if (argc < 2) return 0;
+    std::string cmd = std::string("echo hello ") + argv[argc - 1];
+    std::system(cmd.c_str());
+    return 0;
+}