Having eaten, die in agony as prisoner (8)

I believe the answer is:

detainee

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'prisoner' is the definition.
(I know that prisoner can be written as detainee)

'having eaten die in agony' is the wordplay.
'eaten die' anagrams to 'DETAINEE'.
Though, I'm not sure how the anagram is indicated.

'as' is the link.

Can you help me to learn more?

(Other definitions for detainee that I've seen before include "confined person" , "Prisoner" , "One is held under guard, for political reasons perhaps" , "One penned" , "Someone held in custody" .)

I've seen this clue in The Guardian.

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