fix(weave): exempt started_at from float convert in saved view filters

tests/trace/test_saved_view.py

@@ -6,6 +6,7 @@
 from weave.flow.saved_view import (
     Filter,
     Filters,
+    filter_to_clause,
     filters_to_query,
     query_to_filters,
     to_seconds,
@@ -124,6 +125,27 @@ def test_roundtrip_operators():
         assert filters == filters2
 
 
+def test_number_filter_skips_float_convert_for_typed_columns():
+    """Typed columns (started_at, latency_ms) skip the `$convert` to double; JSON fields keep it."""
+    assert filter_to_clause(
+        Filter(field="started_at", operator="(number): >=", value=1777593600)
+    ) == {"$gte": [{"$getField": "started_at"}, {"$literal": 1777593600.0}]}
+    assert filter_to_clause(
+        Filter(field="started_at", operator="(number): <=", value=1778889599)
+    ) == {"$not": [{"$gt": [{"$getField": "started_at"}, {"$literal": 1778889599.0}]}]}
+    assert filter_to_clause(
+        Filter(field="summary.weave.latency_ms", operator="(number): >", value=100)
+    ) == {"$gt": [{"$getField": "summary.weave.latency_ms"}, {"$literal": 100.0}]}
+    assert filter_to_clause(
+        Filter(field="inputs.score", operator="(number): >", value=5)
+    ) == {
+        "$gt": [
+            {"$convert": {"input": {"$getField": "inputs.score"}, "to": "double"}},
+            {"$literal": 5.0},
+        ]
+    }
+
+
 def test_filter_op_without_client():
     """If we haven't done an init, we don't know what entity/project a non-qualified op name is in."""
     with pytest.raises(

weave/flow/saved_view.py

@@ -154,11 +154,9 @@ def make_eval_op_name(entity: str, project: str) -> str:
 
 VALUELESS_OPERATORS = {"(any): isEmpty", "(any): isNotEmpty"}
 
-# We return a real float from the backend! do not convert to double!
-# When option clicking latency, because we are generating this field
-# manually on the backend, it is actually a float, not a string stored
-# in json, so we need to omit the conversion params from the filter
-FIELDS_NO_FLOAT_CONVERT = {"summary.weave.latency_ms"}
+# Real typed columns (a backend float, a DateTime64), not JSON strings, so they
+# skip the `to: double` cast. toFloat64OrNull on started_at is rejected by ClickHouse.
+FIELDS_NO_FLOAT_CONVERT = {"summary.weave.latency_ms", "started_at"}
 
 
 def py_to_api_filter(filter: tsi.CallsFilter | None) -> tsi.CallsFilter | None: