ID please

OK so I used spent compost  for sowing this years toms and should expect the odd rogue seedling. I'm used to weeds and tomatoes popping up everywhere,  but I've got a rogue something coming up alongside some tomato seedlings and it looks strange/familiar/interesting, but I've no idea what.  Its unlikely to be floral considering the compost was old tomato pots.
For size you'll see an emerging tomato, not yet reached proper leaf stage. What is it?........ Inspiration just hit me, could it be a cucumber, although I'm damned as if I can figure how it got into outdoor tomato compost.

   

It does look like a cucurbit family member so could be a cucumber or a courgette/squash/melon.

Now how am I going to keep a cuc thriving until last frosts? I haven't got the heart to pull it out.

Agree with Veggie

Thay could be a courgette - I would bin it. Waste of space growing something that has cross pollinated...it may not even be edible.

You have a point Scarlet. I may have to be hard hearted. I've plenty of new cucubits waiting to be sown without wasting effort on an unknown. TBH it looks more like a melon to me with 'map lines' on the leaves so that's from the kitchen waste, so definitely a non starter