research: karman reproduce refuses an existing output directory

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

research/karman_reproduce/run.py

@@ -56,7 +56,7 @@ def main():
     here = os.path.realpath(os.path.join(os.path.dirname(__file__), "..", ".."))
     if os.path.realpath(args.out).startswith(here):
         raise SystemExit("--out must be outside the checkout")
-    os.makedirs(args.out, exist_ok=True)
+    os.makedirs(args.out)  # fresh directory only; never overwrite results
 
     sys.dont_write_bytecode = True  # import only: write nothing into the DynamisLab tree
     sys.path.insert(0, os.path.join(args.dynamis, "src"))