1 files changed, 15 insertions, 1 deletions
diff --git a/debug/risc-v-gsp-rm-vm/harness/value_demos/_common.py b/debug/risc-v-gsp-rm-vm/harness/value_demos/_common.py
index 0733c48..ebbc390 100644
--- a/debug/risc-v-gsp-rm-vm/harness/value_demos/_common.py
+++ b/debug/risc-v-gsp-rm-vm/harness/value_demos/_common.py
@@ -17,6 +17,7 @@ import json
 import os
 import shutil
 import sys
+import tempfile
 import time
 
 HERE = os.path.dirname(os.path.abspath(__file__))
@@ -95,11 +96,24 @@ def artifact_dir(name: str) -> str:
     return path
 
 
+def session_dir(root: str, label: str = "session") -> str:
+    """A unique recording dir under ``root``.
+
+    Demos share a fixed artifact root so their reports are discoverable, but
+    two concurrent demo runs (tests, agents) must never share one
+    ``events.jsonl`` or a reader can see a half-written recording.
+    """
+    os.makedirs(root, exist_ok=True)
+    return tempfile.mkdtemp(prefix=f"{label}-", dir=root)
+
+
 def write_json(path: str, payload) -> str:
     os.makedirs(os.path.dirname(path), exist_ok=True)
-    with open(path, "w", encoding="utf-8") as fh:
+    tmp = f"{path}.tmp-{os.getpid()}"
+    with open(tmp, "w", encoding="utf-8") as fh:
         json.dump(payload, fh, indent=2, sort_keys=True)
         fh.write("\n")
+    os.replace(tmp, path)
     return path