fix low level issues

bincio/edit/cli.py

@@ -64,7 +64,7 @@ def _resolve_data_dir(explicit: Optional[str], config_path: Optional[str]) -> Pa
 
     if config_path and Path(config_path).exists():
         import yaml
-        raw = yaml.safe_load(Path(config_path).read_text())
+        raw = yaml.safe_load(Path(config_path).read_text()) or {}
         out = raw.get("output", {}).get("dir")
         if out:
             return Path(out).expanduser().resolve()

bincio/edit/server.py

@@ -506,12 +506,7 @@ async def save_athlete(payload: dict[str, Any]) -> JSONResponse:
         encoding="utf-8",
     )
 
-    # Patch athlete.json in-place (preserves power_curve, updated_at, etc.)
-    data = json.loads(athlete_path.read_text(encoding="utf-8"))
-    data.update(overrides)
-    athlete_path.write_text(json.dumps(data, indent=2, ensure_ascii=False))
-
-    # Re-merge so _merged/athlete.json symlink stays valid
+    # Re-merge — merge_all() applies edits/athlete.yaml on top of athlete.json
     from bincio.render.merge import merge_all
     merge_all(dd)