[BUG] Query anonymization doesn't work in fallback log

What is the bug?
Query anonymization is not working in the fallback log

How can one reproduce the bug?
Write a simple query and add ?format=json to trigger falling back to old engine.

POST /_plugins/_sql?format=json
{
  "query" : """
  SELECT min(DistanceMiles), avg(DistanceMiles), max(DistanceMiles)
    FROM opensearch_dashboards_sample_data_flights
      GROUP BY Carrier
  """
}

Or write a query which is unsupported in V2, e.g JOIN

POST /_plugins/_sql
{
  "query" : """
  SELECT s.FlightNum, s.OriginCityName, d.DestCityName
    FROM opensearch_dashboards_sample_data_flights s
      JOIN opensearch_dashboards_sample_data_flights d
        ON s.DestCityName = d.OriginCityName
  """
}

See this line in the logs

Request SQLQueryRequest(jsonContent={"query":"\n SELECT min(DistanceMiles),avg(DistanceMiles),max(DistanceMiles) FROM opensearch_dashboards_sample_data_flights GROUP BY Carrier\n "}, query=
SELECT min(DistanceMiles),avg(DistanceMiles),max(DistanceMiles) FROM opensearch_dashboards_sample_data_flights GROUP BY Carrier
, path=/_plugins/_sql, format=json, params={pretty=true, format=json}, sanitize=true, cursor=Optional.empty) is not supported and falling back to old SQL engine

Request SQLQueryRequest(jsonContent={"query":"\n SELECT s.FlightNum, s.OriginCityName, d.DestCityName FROM opensearch_dashboards_sample_data_flights s JOIN opensearch_dashboards_sample_data_flights d ON s.DestCityName = d.OriginCityName\n "}, query=
SELECT s.FlightNum, s.OriginCityName, d.DestCityName FROM opensearch_dashboards_sample_data_flights s JOIN opensearch_dashboards_sample_data_flights d ON s.DestCityName = d.OriginCityName
, path=/_plugins/_sql, format=jdbc, params={pretty=true}, sanitize=true, cursor=Optional.empty) is not supported and falling back to old SQL engine

What is the expected behavior?
Logs should show

Request SQLQueryRequest(query=
SELECT MIN ( identifier ), AVG ( identifier ), MAX ( identifier ) FROM table GROUP BY identifier
, path=/_plugins/_sql, format=json, params={pretty=true, format=json}, sanitize=true, cursor=Optional.empty) is not supported and falling back to old SQL engine

Request SQLQueryRequest(query=
SELECT identifier, identifier, identifier FROM table s JOIN table d ON identifier = identifier
, path=/_plugins/_sql, format=jdbc, params={pretty=true}, sanitize=true, cursor=Optional.empty) is not supported and falling back to old SQL engine

What is your host/environment?

• Version 2.15
• Plugins SQL

Do you have any screenshots?
If applicable, add screenshots to help explain your problem.

Do you have any additional context?
Add any other context about the problem.

Reproduce the issue with the documented POST /_plugins/_sql requests, using format=json or an unsupported JOIN to trigger the fallback log. Trace the fallback log's SQLQueryRequest formatting and query anonymization path; done means the log shows anonymized tables, identifiers, and functions rather than the original names and values.