Pronunciation of 一 in 一边 I am struggling with the pronunciation of the 一 in 一边.  The usage I am particularly concerned with is describing simultaneous tasks, as here.  My understanding is that 一 is pronounced as first tone when alone or as an ordinal but fourth tone otherwise, consistent with this similar question about 一个 and this question about 一线城市.  As such, I would expect 一边 to be pronounced yi4 bian1.  However, in the first link above, and also in every dictionary I look at, it is first tone.  What is the correct way to pronounce this word?
Yìbiān would be correct.

For ordinals, it is pronounced yī. In other cases, When followed by fourth tone, it takes the second tone (一对, yí duì). For all other following tones, it takes on the fourth tone.

The reason it is not marked in dictionaries, is because the rules for tone sandhi are few and straightforward. Isolated cases are when a tone is dropped (or replaced by the fifth neutral tone), and those cases are usually indicated.