docs(gov): BAT-018/REQ-043 거버넌스 마감 — Implemented + release-candidate 전환

- REQ-043: Approved → Implemented (BAT-018 PR #14 squash d93c0bc, 팀장 QC PASS, origin/main 머지)
- BAT-018: in-progress → release-candidate (배포 별도 — 미배포)
- dcy-008 생성된 REQ 참조에 Implemented 반영
- srs/index.md Requirement Register 및 Recent Change Log Summary 갱신 (최신 5건)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VHtM5Ws1HKCKQ4JGi6GRb5

docs/srs/Interface/req-043_holdings-cost-basis-read-endpoint.md

@@ -1,6 +1,6 @@
 # REQ-043: GET /v1/portfolios/{id}/holdings/cost-basis 현재 보유 평단(WAC) read 엔드포인트 신설
 
-- Status: Approved
+- Status: Implemented
 - Type: Interface
 - Priority: High
 - Owner: Justin Ko
@@ -64,6 +64,37 @@
 
 ## Change Log
 
+### CHG-20260626-01
+- Date: 2026-06-26
+- Author: Justin Ko (portfolio-hub-dev)
+
+#### Change Summary
+- 상태 `Approved` → `Implemented` — BAT-018 구현 완료, PR #14 squash-merge(d93c0bc) 후 팀장 QC PASS 및 origin/main 머지 확인.
+
+#### Intent
+- BAT-018(batch-lite) 구현·검증 완료: AC-1~11 전부 PASS, 신규 테스트 20개 + 기존 회귀 427개 0 실패(총 447 passed). `calculate_current_wac` 신규 domain 함수, `HoldingsCostBasisResponse` 스키마, GET 엔드포인트 additive 추가. 배포는 별도(미배포 — release-candidate 상태).
+
+#### Acceptance Criteria Delta
+- No change (AC-1~11 유지, 전부 검증 완료).
+
+#### Impacted Area Delta
+- No change.
+
+#### Delivery Trace Delta
+- Batches: BAT-018 → release-candidate
+- Releases: none (미배포)
+
+#### Revalidation Impact
+- Reverification Needed: no
+- Existing Implementation Invalidated: no
+- Status Recommendation: Implemented
+- Follow-up Action: 배포 시 release 문서 작성.
+
+#### Validation Plan
+- BAT-018 verification.md 참조 (AC-1~11 PASS, 447 passed / 0 failed).
+
+---
+
 ### CHG-20260625-02
 - Date: 2026-06-25
 - Author: Justin Ko (portfolio-hub-dev)