fix: align research metadata with live WorldQuant responses

backend/app/research/experiments.py

@@ -27,6 +27,17 @@ def scope_of(settings):
     }
 
 
+def seed_settings(snapshot):
+    """Decode executable settings, retaining returned historical dates in the parent snapshot.
+
+    startDate/endDate are result window metadata absent from POST settings. Unknown
+    execution parameters still fail strict validation rather than being discarded.
+    """
+    return SimulationSettings.model_validate(
+        {k: v for k, v in snapshot.items() if k not in ("startDate", "endDate")}
+    )
+
+
 class Experiments:
     def __init__(self, db):
         self.db = db
@@ -315,7 +326,7 @@ class Experiments:
             [parent_snapshot] if parent_snapshot is not None else await self.parents([body.alpha_id], [])
         )
         original = parents[0]
-        base = SimulationSettings.model_validate(original["settings"])
+        base = seed_settings(original["settings"])
         expression = original["expression"]
         snapshots, _ = await self.inputs(body.input_ids)
         groups = defaultdict(list)