refactor: 重构 schemas 结构，统一枚举定义

docs/plans/2026-03-25-schemas-restructure-design.md

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+# Backend Schemas Restructure Design
+
+**Goal:** Restructure `backend/src/schemas` into clear domain/shared/enums modules while keeping API contracts in `backend/src/v1/*/schemas.py`.
+
+**Architecture:** Move reusable validation models and enums into `schemas/domain`, `schemas/shared`, and `schemas/enums.py`. Keep versioned request/response contracts in `v1/*/schemas.py` and update imports to explicit module paths. Remove legacy aggregate exports and duplicate/empty schema directories.
+
+**Tech Stack:** Python 3.13, Pydantic v2, Ruff, Pytest.
+
+---
+
+## Approved decisions
+
+- Use one-shot hard cut.
+- Keep API contracts in `backend/src/v1/*/schemas.py`.
+- Keep `schemas` as reusable constraints only.
+- Remove implicit root re-export usage.
+
+## Target structure
+
+- `backend/src/schemas/enums.py`
+- `backend/src/schemas/domain/*.py`
+- `backend/src/schemas/shared/*.py`
+- `backend/src/v1/*/schemas.py` (unchanged naming and ownership)
+
+## Validation gates
+
+- `uv run ruff check ...`
+- `uv run pytest ...` for impacted suites
+- `./infra/scripts/dev-migrate.sh migrate`