Tethering spells - what is the mechanism?

The Virtue Tethered Magic (and indirectly some other virtues and even a Mastery ability) allow a magus to 'tether' his spells to another person (or item).
"You can pass control of your non-Ritual spells to others, just as if they were the caster, “tethering” the magic to them for the spell’s duration."

What is the mechanism for this?

What then decides the trigger - the tetherer (the original caster)? the tetheree ('as if' caster)? automatic (next possible target)?

Supposing the tethered spell was Dur: Momentary, Target: Individual - can you tether something fast enough before 'momentary' goes off?
Does the Incantation of Lightning simply go off from the tetheree's hand?
Who then decides which individual is targeted (hit by lightning bolt) - the tetherer or the tetheree?

Assuming the spell was Range: Touch it would go off on the next target touched by the tetheree?
How long could it take before a tetheree touches a target? (and the spell still goes off)
Would concentration checks be required for a tetheree to 'hold' a spell waiting for a target?
Would the tetheree need to be touching a target when the spell is cast for it to work?

Could the tetheree 'refuse' the spell, or prevent it targeting certain targets voluntarily (even if they were the next available target).

Is this the answer that has been searched for in the case of Gift of Vigour? :smiling_imp:

So is this some forbidden subject or is it just that no one anywhere has a clue?

I don't know about either of the above but it's certainly a thread I hadn't seen before now...

As to tethered magic...

I think there's sufficient ambiguity in the virtue description to allow you to play it how you want, but here's how we use it (for my Verditius character).

To tether an effect, you need to touch the recipient; literally passing the spell to it.

Although the spell is cast, it is not released immediately. Remember that a momentary spell lasts for "a moment" and may not simply be a quick flash and then gone. So I have time to tether my spell to an arrow and shoot it over the castle wall before it explodes into light and flame. Similarly, the grog has time to take a tethered Obliteration of the Metallic Barrier from me to the door and use it accordingly.

As for targeting, I let the bearer of the spell choose. I'm sure some troupes would enjoy making "avoid touching the wrong target" rolls, but personally I'd weight all that in the players' favour.

Obviously, if the spell is tethered to an object, then the next potential target that object touches (hears, sees...?) must resist the spell.

Can you refuse to bear the spell? Probably. Not had any need to cover that one and as the text doesn't say anything about it you can make up your own mind.

If you Look at the rules for Hunters Lethal Arrow, then it has a Diamater Duration and the wording in the spell says this is to allow shooting.

So the 'trigger' is when the spell comes into range of a suitable target.

In this case, touch.