I had a bit of a crash at the weekend and snapped a bit off my (carbon) frame. The bit in question is where the e-type mech attaches to to stop it rotating. It's not fixable so I've got a new frame on the way.

But…

I'd quite like to use the old frame as a 1×9. Can I just run a single chainring up front or will the chain jump off (it's a full suspension frame)? Is there a cunning component I can buy or do I have to get lateral with an angle grinder?

You can get a chain device and icsg back plate to mount it to that goes behind the BB cups. Simple as that a e-13 SRS is good though I think superstar do some cheap ones now

surely a band on gear hanger will allow you to run the derailleur ??

anyway, an N-gear jump stop and a bash ring (remove the un-needed rings) and jobs a good un

I guess you are still gonna need a rear mech to run 1×9 so you are screwed.
even if you SS you will still need a sprung tensioner -still screwed.

as I understand it.

Thanks for the pointers I'll investigate further. I got impatient and set about it with assorted power tools. I seem to have it running fine one the road at least (and bumping up and down curbs). If it doesn't work for real riding I'll have a look at the commercial offerings.