feat(holdings): REQ-043 현재 보유 평단(WAC) read — GET /v1/portfolios/{id}/holdings/cost-basis (BAT-018, PR #14)

dcy-008(confirmed)/REQ-043(Approved)/BAT-018. trex-core dcy-034 FR-7 cold-start seed 의존. AC 11/11, QC PASS. worktree+PR 워크플로 첫 파일럿.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VHtM5Ws1HKCKQ4JGi6GRb5

docs/discovery/index.md

@@ -13,3 +13,4 @@
 | dcy-005_20260601_rel-001-feedback-cleanup | 20260601 | REL-001 Feedback 정합화 — ledger_trades.asset_id 명명 / session no_expiry enforcement / health db_enabled | [Discovery](./dcy-005_20260601_rel-001-feedback-cleanup.md) | confirmed |
 | dcy-006_20260605_ledger-trade-write-portfolio-state-return | 20260605 | ledger trade write 회계 책임 단일화 — 응답에 portfolio 상태 포함 + portfolio_ledger/ledger_trades 테이블 통합 (issue #8) | [Discovery](./dcy-006_20260605_ledger-trade-write-portfolio-state-return.md) | confirmed |
 | dcy-007_20260616_daily-trade-history-and-realized-pnl-query-api | 20260616 | 일일 거래내역 + 실현 PnL 조회 API (운영 리포트/프론트 데이터 소스, issue #11) | [Discovery](./dcy-007_20260616_daily-trade-history-and-realized-pnl-query-api.md) | confirmed |
+| dcy-008_20260625_current-holding-wac-cost-basis-read | 20260625 | 현재 보유 종목별 평단(WAC) 조회 API — trex-core 중장기 cold-start 슬롯 평단 seed 의존(교차 발원 trex-core dcy-034 FR-7). GET /v1/portfolios/{id}/holdings/cost-basis | [Discovery](./dcy-008_20260625_current-holding-wac-cost-basis-read.md) | confirmed |