Inept don messed up conclusion (8)

I believe the answer is:

endpoint

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'up conclusion' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'inept don messed' is the wordplay.
'messed' is an anagram indicator (letters get messed up).
'inept'+'don'='ineptdon'
'ineptdon' is an anagram of 'ENDPOINT'.

Can you help me to learn more?

(Other definitions for endpoint that I've seen before include "The last bit" , "goal" .)

I've seen this clue in The Times.

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