If I apply the Careful Spell metamagic to a spell that a creature can choose to fail, and they do, what happens?

Question

Certain spells, like Calm Emotions, allow a character to automatically fail their Saving Throw when resisting the effect:

Each humanoid in a 20-foot-radius sphere centered on a point you choose within range must make a Charisma saving throw; a creature can choose to fail this saving throw if it wishes.

—Calm Emotions, Player's Handbook, pg 221

However, a Sorcerer† casting Calm Emotions could choose to make a character automatically succeed at their Saving Throw with the Careful Spell metamagic:

[...] you spend 1 sorcery point and choose a number of those creatures [that are affected by the spell] up to your Charisma modifier (minimum of one creature). A chosen creature automatically succeeds on its saving throw against the spell.

—Careful Spell, Player's Handbook, pg. 102

So if said sorcerer cast this spell on a group of characters, but chose to protect one of the targets (perhaps so that an existing Charm effect is not suppressed) but the target chooses to fail anyways, what happens? Is the target allowed to make this choice at all, or does the metamagic have precedence over the choice granted by the spell?

^{†It would have to be a Divine Soul Sorcerer, or a Multiclassed Sorcerer, since Calm Emotions is not on the Sorcerer Spell List}

Answer 1

The order of events matter: They succeed

In the scenario you provide, the sorcerer is casting the spell with the metamagic that allows them to choose who automatically passes the saving throw.

All but empowered spell metamagic uses the following language:

When you cast a spell...

This clearly states that metamagic is used at the time of casting. The language used for empowered spell references that by allowing it to be used separately:

You can use Empowered Spell even if you have already used a different Metamagic option during the casting of the spell.

This is the first event in the sequence. It's possible for this to be ended early by mechanics like counterspell, but once complete, the spell is cast with the requirements provided through the metamagic (target X succeeds automatically.)

At this point, the spell is complete and the saving throw result is predetermined for Target X. Because of that, Target X no longer has the option to fail because that option was removed with the metamagic determining success.

Here's the timeline:

1. Sorcerer casts spell with metamagic
2. Metamagic predetermines saving throw result
3. Spell is fully cast and complete along with any predetermined results
4. Targets resolve spell with predetermined saving throw result

The opportunity for the target to choose to fail was removed once the spell casting completed with the metamagic that predetermined the result.

Answer 2

The target automatically succeeds at the Saving Throw because Careful Spell is the more specific effect

Citing the general rule of Specific beats General:

Remember this: If a specific rule contradicts a general rule, the specific rule wins.

—Specific Beats General, Player's Handbook, pg. 7

In this situation, I would rule that the Less Specific Rule is the rule that Calm Emotions permits a target to automatically fail at their saving throw.

Conversely, the More Specific Rule is the rule that with this specific casting of the spell using this metamagic, the creature targeted by Calm Emotions automatically succeeds at their saving throw.

So because Careful Spell is more specific, it takes precedence.