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In spaces each file has a distinct setting of public or private. What you are referring to as a private bucket, simply means that the files list of that particular space can not be viewed publicly.
However, regardless of whether you set a Spaces bucket to private or public you still manage each files permissions individually, meaning any file inside of the space can be set to public or private.
So, yes, you can have a public file inside of space that is set to private (restricted directory listing).
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