How does Eldritch Shot interact with multiple-attack spells?

Question

Eldritch Archers get to launch spells that have a spell attack roll (a surprisingly limited list as of yet) using a Strike with Eldritch Shot

Activate [Three Actions] Eldritch Shot; Requirements You are wielding a bow;

Effect You Cast a Spell that takes 1 or 2 actions to cast and requires a spell attack roll. The effects of the spell do not occur immediately but are imbued into the bow you're wielding. Make a Strike with that bow. Your spell flies with the ammunition, using your attack roll result to determine the effects of both the Strike and the spell. This counts as two attacks for your multiple attack penalty, but you don't apply the penalty until after you've completed both attacks.

Scorching ray allows you to launch 1-3 rays depending on how many actions is used casting the spell (similar to the function of magic missile).

For each additional action you use when Casting the Spell, you can fire an additional ray at a different target, to a maximum of three rays targeting three different targets for 3 actions. These attacks each increase your multiple attack penalty, but you don’t increase your multiple attack penalty until after you make all the spell attack rolls for scorching ray. If you spend 2 or more actions Casting the Spell, the damage increases to 4d6...

How would using scorching ray work with Eldritch Shot? I see a few possibilities (although there may be a more correct interpretation than any of these)

1. Scorching ray and similar spells are not a valid spell choice for Eldritch Shot and cannot be used at all
2. Scorching ray is valid choice, but only in its 1-action iteration; other spells would need separate adjudication
3. You can cast multi-target spells with Eldritch Shot; you can use the 2-action version of scorching ray to get the bonus damage, but you only get a single attack and the other is wasted
4. You successfully cast the spell regardless of Eldritch Shot; you can use your bow for one of the attacks provided by scorching ray and select another target (within the spell's range) for its second attack

Answer 1

Scorching ray is valid choice, but only in its 1-attack iteration

The real key here is in the Effect line of Eldritch Shot:

You Cast a Spell that takes 1 or 2 actions to cast and requires a spell attack roll.

Because this specifies * a * spell attack roll, this ability only works with with spells that make a single spell attack roll.

So for scorching ray, you can spend up to two actions casting the spell and pair it with Eldritch Shot. The limitation is that you can fire only one ray no matter how many actions you spend, and that you can only use up to 2 actions because of Eldritch Shot. You would still get the damage increase from using 2 actions.

This same understanding can be used to adjudicate most other spells that have variable numbers of spell attack rolls—only the single attack roll version would work with Eldritch Shot.