If the scenario specifies that you start with a certain spell pre-cast (e.g. Mitra's Halo in "In the Clutches of the Picts"), must that hero put gems on the spell, or is it free?
If you must assign gems, do you take them from the reserve or from the fatigue area?
It doesn't say to, and i assume "no" because one can assume the caster has had time to recover the casting cost by the time the scenario actually starts.
If a hero has to pay the gem cost as part of setup, that would also apply to OL units which start with spells cast on them. i've seen no mention of anyone having to explicitly pay that cost as part of the setup.