[solo applicant] have my mid-tailor section-add land in the quarry without corrupting the in-flight tailor

Walk the cross-cutting story scenarios that span pipeline + collaboration: three actors converging after an extract, adding a column mid-score, switching the view group mid-drag, friend-edits during a tailor, the agent-tailors-while-user-offline path, mid-tailor section adds, and the no-workspace-delete safety. These specs catch races that single-actor suites cannot see.

Proof set for User adds new section while LLM tailor in flight — tailor uses pre-add tree (its snapshot was taken first)