# BAT-010 Backend core layering (Phase 0~3)

- Profile: standard
- Status: release-candidate
- Included REQ: REQ-013, REQ-014
- Discovery: dcy-010
- Owner: 렛저장인
- Date (KST): 2026-07-03

## 목표

REQ-013/REQ-014에 따라 `service.py` giant implementation과 `db.py` persistence 집중을 application / infrastructure / adapter seam으로 분리한다. 동시에 top-level facade/shim 호환, MCP tool contract, Streamlit 핵심 화면, additive migration discipline을 유지해 Phase 4+ 분리의 안전한 기반을 만든다.

## 산출물

- `jarca_ledger_mcp/application/` phase-0~3 service modules + shared helpers
- `jarca_ledger_mcp/infrastructure/sqlite/` connection/schema/migration split
- `jarca_ledger_mcp/adapters/mcp/server.py` + top-level `server.py` shim
- `jarca_ledger_mcp/adapters/streamlit/service_gateway.py` + dashboard import seam 정렬
- `service.py` / `db.py` compatibility facade & shim
- full pytest / MCP discovery / browser smoke evidence
- `docs/project-structure.md`, `docs/runtime-flows.md` baseline updates
- BAT-010 planning/design/implementation/verification documents

## 범위 제한

- Phase 4+ transactional write/import/advanced workflow 분리
- 신규 HTTP adapter 추가
- response envelope, tool names, dashboard IA 재설계
- destructive DB migration

## 문서

- `planning.md`: Phase 0~3 delivery plan, risks, validation gate
- `design.md`: layering/seam/shim design
- `implementation.md`: changed files, execution log, validation commands
- `verification.md`: AC mapping, PASS/FAIL, REQ Implemented decision