The ECSC should not be used for complex, risky design and construct projects. As you have discovered it contains no procedures for the submission of design for acceptance, undertakings to others (collateral warranties), intellectual property or in respect of design liability and insurance against such.
In the absence of this, when used in the UK, the ECSC will have terms implied from statute, in particular the Supply of Goods and Services Act 1982 which says that the materials supplied under the contract are of satisfactory quality and that the finished work will be reasonably suitable for the purpose for which the Contractor knows it is required. If the Client can prove that the Contractor has failed in either regard then the Contractor can be held liable. In respect of design this would normally involve notifying insurers however the Contractor's insurance won't extend to work done under the ECSC so there will inevitably need to be some negotiation between Client and Contractor with the Client ultimately seeking satisfaction through adjudication if negotiations fail to get things resolved.
In the absence of this, when used in the UK, the ECSC will have terms implied from statute, in particular the Supply of Goods and Services Act 1982 which says that the materials supplied under the contract are of satisfactory quality and that the finished work will be reasonably suitable for the purpose for which the Contractor knows it is required. If the Client can prove that the Contractor has failed in either regard then the Contractor can be held liable. In respect of design this would normally involve notifying insurers however the Contractor's insurance won't extend to work done under the ECSC so there will inevitably need to be some negotiation between Client and Contractor with the Client ultimately seeking satisfaction through adjudication if negotiations fail to get things resolved.