By combining a casting of Mount with Carry Companion can a wizard create in effect a single-use Talisman of the Summoned Steed?
It would still disappear at the end of the duration of the Mount spell, if that's what you mean. It would still work for the duration of the Mount spell, but you can't use this to get around that duration limit.
So essentially, you could pocket the mount to use later, but once re-activated the normal duration kicks in? That's basically how I see this. Am I wrong? The duration of the carry spell is listed as permanent(until discharged).
No. In the same way a Summon Monster I creature's duration of 1 round/level isn't changed to 1 minute/level when it's within the area of a Bless spell. Spell effects active on the summoned creature do not change its base duration unless specifically stated to do so.
Q: But don't the rules for Conjuration (Summoning) spells say an object remains summoned unless specifically stated otherwise?
A: You didn't summon an object. You summoned a creature and then turned it into an object. Its original duration continues to expire no matter what form it's in.
Q: But doesn't the Carry Companion spell say the creature remains in stone form unless the spell is broken?
A: Antimagic Field is an excellent example of the interaction of spell duration under an effect that overrides it. Spell durations continue to expire even while under the effect of another spell that changes their functioning.
ah. makes sense. thank you.