A mine rediscovered in a Welsh strait (5)

I believe the answer is:

menai

I'm a little stuck... Click here to teach me more about this clue!

'a welsh strait' is the definition.
(I've seen this in another clue)

'a mine rediscovered' is the wordplay.
'a mine' anagrams to 'MENAI'.
Though, I am not sure how the anagram is indicated.

'in' is the link.

Can you help me to learn more?

(Other definitions for menai that I've seen before include "Strait between Anglesey and Welsh mainland" , "Name of Welsh strait" .)

I've seen this clue in the Evening Standard.

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