Large UInt64 values come back wrong because they exceed JavaScript's max safe integer (2^53 - 1). A value like 1875924584784080993 becomes 1875924584784081000. This also happens for other large integer Clickhouse types.

I can manually wrap columns with toString() in every query, but if I don't know that it's necessary, I will just work with broken data.

I think this should be either specified somewhere in the docs/MCP description, or some automatic solution should be provided (for example wrap such types as a string).