some fixes

python_app/orchestration/config_writer.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import json
+import os
 from pathlib import Path
 
 from python_app.models.run_config_model import RunConfigModel, parse_combos_from_text
@@ -41,12 +42,25 @@ class ConfigWriter:
             asset.bundle_path = str(bundle_path)
 
     def write(self, config: RunConfigModel, output_path: Path) -> Path:
-        """Write run configuration JSON file."""
+        """Atomically write run configuration JSON file.
+
+        Mirrors ProcessingLiveConfigWriter: dump to a sibling .tmp, flush+fsync to
+        durably commit the bytes, then os.replace() onto the destination. The replace
+        is atomic, so a C++ consumer can never observe a half-written config (which
+        would abort it with an opaque JSON parse error), even across a crash or power
+        loss mid-write on the SD-card-backed Pi.
+        """
         output_path.parent.mkdir(parents=True, exist_ok=True)
         # allow_nan=False: a stray NaN/Infinity must fail loudly here in Python
         # rather than serialize to a non-standard token that aborts every C++
         # consumer at startup with an opaque JSON parse error.
-        output_path.write_text(json.dumps(config.to_dict(), indent=2, allow_nan=False), encoding="utf-8")
+        serialized = json.dumps(config.to_dict(), indent=2, allow_nan=False)
+        tmp_path = output_path.with_suffix(output_path.suffix + ".tmp")
+        with open(tmp_path, "w", encoding="utf-8") as handle:
+            handle.write(serialized)
+            handle.flush()
+            os.fsync(handle.fileno())
+        os.replace(tmp_path, output_path)
         return output_path