WTO and Lisbon

The real answer to arguments about whether Ireland can veto the WTO deal lies in the WTO system itself and how it interacts with the EU voting system.
The WTO operates on the principle that nothing is agreed until everything is agreed.  The WTO Doha round covers a huge number of policy areas. Lisbon and the EU treaties provide for some areas to be decided by QMV and some by unanimity.
However any WTO agreement is accepted or rejected in total, it is not taken bit by bit.
Therefore if unanimity applies to one area of the WTO agreement it applies to all. Article 188 (207) states clearly that agreements covering trade and services are subject to unanimity after Lisbon.
These items are clearly on the WTO agenda so any agricultural deal in the WTO will be subject to unanimity after Lisbon.