Why: establish the authorized task workspace and its initial baseline.
Evidence: preserved precheck receipt in .task/feature-pin-backend-ext8b.md; R0=a47dc76f4b1f8836a70d10c7397e390dc472cdeb.
Impact: task metadata only; the feature workspace starts at a47dc76f4b.
Refs: .task/feature-pin-backend-ext8b.md