Implement BAT-011 transactional write service split

docs/batches/bat-011_20260703_transactional-write-service-split/planning.md

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+# BAT-011 Planning
+
+## Scope
+
+- Implement REQ-015: transactional write path(account / transaction / budget / category rule-category mutation)를 더 좁은 write-oriented application module로 분리한다.
+- Preserve top-level service facade, MCP adapter, Streamlit gateway, dashboard call signatures and response envelope contracts.
+- Leave import/advanced workflow split for follow-up REQ/BAT under dcy-011.
+
+## Dependencies
+
+- dcy-011 confirmed Discovery and Approved REQ-015.
+- BAT-010 application/adapters baseline.
+- Existing pytest regression and contract-sensitive tests.
+
+## Work plan
+
+1. Create write-oriented application modules for accounts / transactions / budgets / category rules.
+2. Move concrete mutation implementations into those modules and keep existing broad modules as compatibility delegation layers where needed.
+3. Update `application/__init__.py` and `service.py` import surface to re-export the new modules without changing public API.
+4. Run focused syntax + regression validation, then full pytest if focused checks remain green.
+5. Update batch implementation/verification evidence and promote REQ/BAT state if ACs are satisfied.
+
+## Design Gate
+
+- Result: standard batch 유지.
+- Reason: package boundary 변경, compatibility delegation, category/account/transaction write contract preservation, regression evidence 정리가 함께 필요하므로 planning/design/verification depth가 필요하다.
+
+## Risks and mitigations
+
+- Hidden import coupling after write extraction: mitigate by preserving re-export layers and running full pytest.
+- Envelope drift on mutation responses: mitigate by preserving existing function signatures and contract-sensitive tests.
+- Category rule/category mutation helpers may still share read-side helpers: mitigate by extracting only write-focused logic first and leaving broad read/report paths untouched in this batch.