Continue protecting cupola, a positive sign for the future (4,4)

I believe the answer is:

good omen

'a positive sign for the future' is the definition.
(a good sign)

'continue protecting cupola' is the wordplay.
'continue' becomes 'go on' (synonyms).
'protecting' indicates putting letters inside (inserted letters are held or protected).
'cupola' becomes 'dome' (architectural term).
'goon' placed around 'dome' is 'GOOD OMEN'.

I've seen this clue in The Guardian.

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