Why: turn the approved recovery design into reviewable cross-component implementation and validation steps.
Evidence: six tasks and thirty steps mapped to the spec; review-focus tests, local links and diff checks pass.
Impact: plan and validation status only; code and paid model execution remain NOT_RUN.
Refs: docs/proposals/2026-10-14-fast-slow-u3-r04-reliable-first-checkpoint-implementation-plan.md; docs/reports/2026-10-13-fast-slow-u2-u3-validation.md