backlog-refinementlisted

## Inputs - `backlog.json` → items with status: draft - `requirements.md` - `docs/requirements-benchmark.md` — prior-art / similar-case findings with per-item dispositions produced by Requirement Definition (reuse first before any refinement-time web search; may be absent on a pre-brief / resumed project) - Count of existing refined PBIs (WIP check) ## Outputs - `backlog.json` → items[].status: refined, acceptance_criteria (non-empty), ux_change, demo_plan (non-empty for kind=code), design_doc_paths, priority (non-negative integer) - Every refined PBI carries a **settled approach/method** — the solution direction is recorded in `description` (and the doc it will shape is named in `design_doc_paths`), with no PO-only spec question about it left open (see Steps 3.a2 / 3.a3) - `.scrum/po/decisions.json` (agent mode) — any `spec_clarification` ruling emitted during refinement, logged via `append-po-decision.sh` ## Preconditions - state.json phase: "backlog_created" or "retrospective" - backlog.json has ≥1 draft PBI - Refined PBI count < WIP cap 12 ## PO seat resolution (po_mode) The PO-clarification points below (Step 3.a3, and any PO-only spec question surfaced during 3.a2 research) resolve to the PO seat per `.scrum/config.json.po_mode` and `../../rules/scrum-context.md` § PO seat resolution: - `human` (default) → the SM asks the user in the main session and waits for a natural-language reply. - `agent` → the SM routes `[<pbi-id>] PO_DECISION_REQUEST k