Cheery pat irked classic model (9)

I believe the answer is:

archetype

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

'model' is the definition.
(I know that archetype is a type of model)

'cheery pat irked classic' is the wordplay.
'cheery pat' anagrams to 'ARCHETYPE'.
Though, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for archetype that I've seen before include "Original, prototype" , "Original model from which others are copied" , "Very characteristic example" , "They caper about like original model" , "Perfect example" .)

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

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