Negotiate half-half treat (4,3)

I believe the answer is:

hash out

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'negotiate' is the definition.
(I've seen this in another clue)

'half-half treat' is the wordplay.
'half' indicates taking half.
'treat' becomes 'shout' (I am not sure about this - if you are sure you should believe this answer much more).
'half' halved is 'ha'.
'ha'+'shout'='HASH OUT'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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