Master spy shrouding measure in extreme secrecy (6)

I believe the answer is:

smiley

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'master spy' is the definition.
'smiley' can be an answer for 'spy' (John le Carre character George Smiley). I am unsure of the 'master' bit.

'shrouding measure in extreme secrecy' is the wordplay.
'shrouding measure' becomes 'mile' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'extreme' suggests removing the centre.
'secrecy' with its middle removed is 'sy'.
'mile' put within 'sy' is 'SMILEY'.

Can you help me to learn more?

(Other definitions for smiley that I've seen before include "Cheerful emoticon" , "Grinning face symbol" , "Spymaster" , "sounds cheerful" .)

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

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