Deregister VantageLogger on delete and add Decimal cast test

- DELETE /vantage/delete now removes the in-memory VantageLogger from
  litellm.callbacks via remove_callbacks_by_type, preventing the
  scheduler from continuing to fire exports with stale credentials
- Add test_should_cast_decimal_columns_to_float covering the
  Decimal→Float64 cast in FocusCsvSerializer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

litellm/proxy/spend_tracking/vantage_endpoints.py

@@ -547,6 +547,13 @@ async def delete_vantage_settings(
             where={"param_name": VANTAGE_SETTINGS_PARAM_NAME}
         )
 
+        # Deregister in-memory VantageLogger so the scheduler stops firing
+        from litellm.integrations.vantage.vantage_logger import VantageLogger
+
+        litellm.logging_callback_manager.remove_callbacks_by_type(
+            litellm.callbacks, VantageLogger
+        )
+
         verbose_proxy_logger.info("Vantage settings deleted successfully")
 
         return VantageInitResponse(

tests/test_litellm/integrations/focus/test_csv_serializer.py

@@ -30,5 +30,18 @@ def test_should_return_header_only_for_empty_frame():
     assert len(lines) == 1  # header only
 
 
+def test_should_cast_decimal_columns_to_float():
+    frame = pl.DataFrame(
+        {"BilledCost": [1, 2], "ServiceName": ["openai", "anthropic"]}
+    ).cast({"BilledCost": pl.Decimal(18, 6)})
+    serializer = FocusCsvSerializer()
+    result = serializer.serialize(frame)
+
+    lines = result.decode("utf-8").strip().split("\n")
+    # Should use floating-point notation (e.g. "1.0") not fixed-point ("1.000000")
+    assert "1.000000" not in lines[1]
+    assert lines[1].startswith("1.0,")
+
+
 def test_extension_should_be_csv():
     assert FocusCsvSerializer.extension == "csv"