Enrol Lead Finder

Enrol segments' EXISTING leads into one arm of a lead-finder experiment.

Deliberately not agent inject: this writes ab_assignment and nothing else — no search, no new leads, no re-rank, nothing that changes which email goes out or when. It is how the instrument gets pointed at live data before an experiment depends on the readout, and how an agent drives an experiment without a button.

Write-scoped, and restricted to lead_finder experiments: the same statement aimed at a visitor test would quietly rewrite a cohort somebody is reading.