When you are casting a spell you already control it at this point. (otherwise reverse magic does not make sense.) I believe The spell type is also defined - otherwise how can we know if nullify should trigger? (only incan. and ench).
Correct, control is granted at step 1) casting a spell:
Controller:
"Each spell or object in the game is controlled by the player who cast it. The controller may use and act with that object, and makes all decisions and choices for that spell or any abilities that object may have. Exception: Equipment is controlled by the Mage it is attached to."
However when you look at step 3)
Step 3: Resolve Spell At this point, the spell takes effect. The spell type (e.g., conjuration) and the text on the spell card determine the effects of the spell. If you have cast an attack spell, you must now resolve the attack. When a spell resolves, if you find that the target of the spell is no longer a legal target or has moved, then the spell is cancelled.
The game does not register that you are casting a specific type of spell until this step, which you never get to in the above example, and so wardstone will not trigger.