How to interpret 全然 + positive adjective + とは思わない

Question

As explained in this question, I know that 全然 used with positive adjective means "completely, entirely", while when it is used with negative adjectives/verbs it means "not at all, absolutely not". However, I don't know how to interpret the following dialogue (note that there's a space between 全然 and 綺麗):

A: 私は綺麗だと思う？

B: 全然　綺麗とは思わないよ。

Which of the following translations is correct?

1) I don't think you are entirely beautiful. [you are beautiful but you lack something]

2) I think you are not beautiful at all.

I think number 1 is correct, but I am not sure. Thank you for your help!

Answer 1

While 全然 is often used in positive sentences these days, this adverb is still basically a negative polarity item, and it has a strong affinity for a following negative expression within the sentence. This means, in this case, 全然 modifies 思わない, "I don't think at all (that ...)" regardless of the space or comma after it. This is also true in conversations where you cannot use commas. The sentence has the same meaning as 綺麗だとは全然思わないよ. (Of course commas can disambiguate things in some cases, though)

To say Sentence 1, you need to choose another adverb and say, for example, "すごい綺麗だとは思わないよ" or "100%綺麗だとは思わないよ". Actually these are still ambiguous, but at least these tend to mean 1 simply because most (non-NPI) adverbs modify something right after it.

EDIT: As l'électeur pointed out, 全然 can modify 綺麗 in a rare context where someone has just used 全然 clearly in a positive sentence. In such a case, 全然綺麗と is a direct quote and the sentence would mean something like "全然綺麗 is an overstatement". But it's still much better to disambiguate using brackets in writing, like:

A: え、Cさん全然綺麗じゃん。
B: 「全然綺麗」とは思わないよ。

EDIT: Please also recheck the usage of 全然 in positive sentences. Read Boaz Yaniv's answer in your link. 全然 in a positive sentence is used to negate someone's prior expectation, and it rarely translates to "completely".

Answer 2

「全然{ぜんぜん}　綺麗{きれい}とは思{おも}わないよ。」

With that space (or a comma instead), it would be most natural to assume that 「全然」 would modify the verb 「思わない」 rather than the adjective「綺麗」. Thus, the sentence would mean:

"I don't think at all that (someone/something) is pretty."

If the space were not there and the sentence were uttered as a response to another person's statement like 「全然綺麗じゃん。」(meaning "(Someone/something) is quite pretty.") , then it could be a different story altogether.

「全然綺麗とは思わない。」, in that context, would mean "(I disagree.) I don't think (someone/something) is all that pretty." In this case, 「全然」 modifies the adjective 「綺麗」.