Crossword Genius

Though heroic, poor Ivan's intervention is not going to work (3-6)

Ross

I believe the answer is:

non-viable

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

'intervention is not going to work' is the definition.
I can't judge whether this defines the answer.

'though heroic poor ivan's' is the wordplay.
I cannot really understand how this works, but
an anagram of 'ivan' is 'nvia' which is present in the answer.
The remaining letters 'noble' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

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