…lines

The mixing MO creation in _action_done created move lines with qty_done
first, then called action_assign expecting Odoo to merge the reservation
into those existing lines. This merge relies on a UoM round-trip check
in _update_reserved_quantity that fails when the quant quantity has more
decimal precision than the UoM rounding allows. When the merge fails,
a second line is created for the same lot — one with only product_uom_qty
and one with only qty_done — making the MO impossible to complete
("cannot unreserve more products than you have in stock").

The fix follows the standard Odoo pattern: call action_assign first to
create proper reservation lines, then set qty_done on those lines by
matching lot_id. This eliminates the dependency on the merge and prevents
split lines regardless of UoM rounding configuration.