Schizopyga frigida

I collected a Clubiona spider for identification (it turned out to be Clubiona terrestris) without noticing the wasp larva (or egg?) that was attached to the rear of its cephalothorax (actually I did notice something there but I didn't twig what it was). It was only later when I came to identify the spider and found that most of its abdomen was missing but there was a live adult wasp in the pot that the penny dropped. I am ssuming the thing attached to the spider originally was a larva rather than an egg as it was kind-of larva-shaped, but I'm wondering if it could have been the egg? Something remained there after metamorphosis was complete, so if it was an egg this could be the remains of the opened egg, or if it was a larva then it must be the exuvia of a non-final instar (do these wasp larvae even have multiple instars?). There was evidence of a pupal coccoon in the pot and the adult insect was identified using the RES key for subfamily Pimplinae, though after I'd already got an indication that it might be this species from ObsIdentify).

female Schizopyga frigida showing larva (?) on Clubiona terrestris, Cranwich Camp (Norfolk, UK), 21st March 2025, and exuvia (?) on same spider after the sider's abdomen was mostly eaten, vacated pupal coccoon and the adult insect that emerged, all photographed on 9th April 2025