Mission Run Overview
Mission Run: docs/plans Tier 3 Closeout
Finish the docs/plans Tier 3 curation: retire stale plans, add the last two domain plans, migrate them into a domains/ cluster, and add a durable throughline marker.
Following PR #3324's domain-throughline model, this mission completes the docs/plans working surface: it retires shipped/superseded plan clusters (evidence-gated, roadmap deferred), authors the last two domain plans (packs-extraction and api-dashboard) with explicit scope boundaries, migrates all four domain plans into a docs/plans/domains/ cluster, and adds a machine-distinguishable 'durable' doc_status marker so throughlines are never swept. Scope A of a two-mission split; the doctrine schema diagrams + PlantUML docsite rendering are a separate follow-on mission (Scope B).