Can I get LCP out of a run as a recorded number, given budgets are not enforced?

I have read the workshop chapter, so I know @perf does not gate anything today and I am not asking for the gate.

What I want is the measurement recorded per run so I can watch it drift across a quarter. The contracts already reserve an attachment name sdods/perf/<step> and a per-step file perf/NN.json, and the run types carry an optional perf field, so the shape exists.

Two questions:

1. Is anything writing to those names today, or are they reserved for something that does not exist yet?
2. If I attach my own JSON under sdods/perf/<step> from a step I write, does the ingest pick it up into the run record, or does it need a matching column before it becomes queryable?

Happy to write the collection step. I would just rather write it into the shape that is going to be filled in than invent a parallel one.