For hyper, append lets keep it simple:

• Column name matching
• If extra column, then we should error
• If missing column then we should warn but write with nothings
• If type mismatch then we should error
• No attempt to be clever with primary keys etc
• If in Backup/Overwrite then we just drop the table and add a new one

This is basically same as Delimited but we allow using positional column match