Restrict Invoice created from SO

This module changes the customer invoice form so that lines created from a Sales Order are protected against manual editing.

When you open a customer invoice (the account.move form), the invoice lines list normally lets you pick a product, change the quantity and change the unit price. With this module installed, each line that is linked to a Sales Order line is shown with those three columns locked: the Product, the Quantity and the Unit Price can no longer be typed over.

• The lock applies only to lines that really come from a Sales Order; lines added manually on the invoice stay fully editable.
• The rule is applied automatically based on the link between the invoice line and the sales order line, so no user action is needed.
• It affects the invoice lines table on the customer invoice screen.

The module does not add any new menu, button, report or scheduled action. It only extends the standard invoice form and relies on the Sales Order link already stored on the invoice line. It works together with the Sales and Invoicing apps (sale_management).