Do not write 'original_session_id' to table if no change

We had previously added a record of sanitization effects through the 'original_session_id' column

But there is no need to write this if sanitization had no effect on the values; do not write the column at all if this happens

Locate the sanitization logic and the code that writes the original_session_id column, then trace how unchanged values are detected. Verify that sanitization still records original_session_id when values change, but omits the column entirely when sanitization has no effect.

Written by the indexing model from the issue text.