fix(m0): 迁移可执行 + 测试全绿（33 条）

跑通迁移与测试后修掉的真问题：

- alembic 0001：asyncpg 走预备语句，一次 execute 只能一条 SQL。
  CREATE FUNCTION / CREATE POLICY / GRANT 全部拆成单语句逐条执行，
  否则报 "cannot insert multiple commands into a prepared statement"。
- 创建工作区：ORM flush 只按 relationship 排序，裸外键不算数，
  member 可能先于 workspace 落地撞 FK。改为先 flush workspace 再插 member。
- datetime.UTC 是 3.11+ 才有的，本机 3.10 直接 ImportError。改用 timezone.utc。
- 幂等中间件：原来会缓存 4xx。校验失败被缓存后，用户改对参数仍拿到同一个 422。
  改为只缓存 <400。
- 发码节流窗口改为可配置 SMS_THROTTLE_SECONDS（测试置 0），
  节流用例自己显式打开，避免"整库关掉节流"导致节流从未被验证。
- 租户隔离用例：pytest.raises(Exception) 改为精确的 ProgrammingError，
  否则任何异常都会让"应用角色不能建表"这条断言假通过。

验收：pytest 33 passed；ruff check / format 通过；真机跑 uvicorn，
/health、/version、登录、建工作区、列表、/auth/me 全通。

backend/alembic/env.py

@@ -5,11 +5,11 @@ from __future__ import annotations
 import asyncio
 from logging.config import fileConfig
 
-from alembic import context
 from sqlalchemy import pool
 from sqlalchemy.engine import Connection
 from sqlalchemy.ext.asyncio import async_engine_from_config
 
+from alembic import context
 from app.config import get_settings
 from app.models import Base
 

backend/alembic/versions/0001_init.py

@@ -19,57 +19,76 @@ depends_on: str | Sequence[str] | None = None
 
 APP_ROLE = "dadao_app"
 
-HELPER_SQL = """
-CREATE OR REPLACE FUNCTION app_ws_id() RETURNS uuid
-LANGUAGE sql STABLE AS $$
-  SELECT nullif(current_setting('app.ws_id', true), '')::uuid
-$$;
+# 说明：asyncpg 走"预备语句"执行，**一条 execute 里只能有一条 SQL**，
+# 多条语句会报 `cannot insert multiple commands into a prepared statement`。
+# 所以这里按语句拆成元组，逐条执行。
+HELPER_STATEMENTS: tuple[str, ...] = (
+    """
+    CREATE OR REPLACE FUNCTION app_ws_id() RETURNS uuid
+    LANGUAGE sql STABLE AS $$
+      SELECT nullif(current_setting('app.ws_id', true), '')::uuid
+    $$
+    """,
+    """
+    CREATE OR REPLACE FUNCTION app_user_id() RETURNS uuid
+    LANGUAGE sql STABLE AS $$
+      SELECT nullif(current_setting('app.user_id', true), '')::uuid
+    $$
+    """,
+)
 
-CREATE OR REPLACE FUNCTION app_user_id() RETURNS uuid
-LANGUAGE sql STABLE AS $$
-  SELECT nullif(current_setting('app.user_id', true), '')::uuid
-$$;
-"""
+POLICY_STATEMENTS: tuple[str, ...] = (
+    # ── workspace：本租户 OR 我是其成员（用于"我加入了哪些工作区"）──
+    "ALTER TABLE workspace ENABLE ROW LEVEL SECURITY;",
+    """
+    CREATE POLICY workspace_isolation ON workspace
+      USING (
+        id = app_ws_id()
+        OR id IN (SELECT m.workspace_id FROM member m WHERE m.user_id = app_user_id())
+      )
+      WITH CHECK (id = app_ws_id());
+    """,
+    # ── member：本租户成员 OR 我自己那条 ──
+    "ALTER TABLE member ENABLE ROW LEVEL SECURITY;",
+    """
+    CREATE POLICY member_isolation ON member
+      USING (workspace_id = app_ws_id() OR user_id = app_user_id())
+      WITH CHECK (workspace_id = app_ws_id());
+    """,
+    # ── invitation ──
+    "ALTER TABLE invitation ENABLE ROW LEVEL SECURITY;",
+    """
+    CREATE POLICY invitation_isolation ON invitation
+      USING (workspace_id = app_ws_id())
+      WITH CHECK (workspace_id = app_ws_id());
+    """,
+    # ── audit_log：只增不改，租户内可见 ──
+    "ALTER TABLE audit_log ENABLE ROW LEVEL SECURITY;",
+    """
+    CREATE POLICY audit_log_isolation ON audit_log
+      USING (workspace_id = app_ws_id())
+      WITH CHECK (workspace_id = app_ws_id());
+    """,
+    # ── 授权：应用角色没有 DDL、没有 BYPASSRLS，只能读写到自己该看的数据 ──
+    f"GRANT USAGE ON SCHEMA public TO {APP_ROLE};",
+    (
+        "GRANT SELECT, INSERT, UPDATE, DELETE ON "
+        f"workspace, app_user, member, invitation, audit_log TO {APP_ROLE};"
+    ),
+    (
+        "ALTER DEFAULT PRIVILEGES FOR ROLE dadao_owner IN SCHEMA public "
+        f"GRANT SELECT, INSERT, UPDATE, DELETE ON TABLES TO {APP_ROLE};"
+    ),
+)
 
-POLICY_SQL = f"""
--- ── workspace：本租户 OR 我是其成员（用于"我加入了哪些工作区"）──
-ALTER TABLE workspace ENABLE ROW LEVEL SECURITY;
-CREATE POLICY workspace_isolation ON workspace
-  USING (
-    id = app_ws_id()
-    OR id IN (SELECT m.workspace_id FROM member m WHERE m.user_id = app_user_id())
-  )
-  WITH CHECK (id = app_ws_id());
 
--- ── member：本租户成员 OR 我自己那条 ──
-ALTER TABLE member ENABLE ROW LEVEL SECURITY;
-CREATE POLICY member_isolation ON member
-  USING (workspace_id = app_ws_id() OR user_id = app_user_id())
-  WITH CHECK (workspace_id = app_ws_id());
-
--- ── invitation ──
-ALTER TABLE invitation ENABLE ROW LEVEL SECURITY;
-CREATE POLICY invitation_isolation ON invitation
-  USING (workspace_id = app_ws_id())
-  WITH CHECK (workspace_id = app_ws_id());
-
--- ── audit_log：只增不改，租户内可见 ──
-ALTER TABLE audit_log ENABLE ROW LEVEL SECURITY;
-CREATE POLICY audit_log_isolation ON audit_log
-  USING (workspace_id = app_ws_id())
-  WITH CHECK (workspace_id = app_ws_id());
-
--- ── 授权：应用角色没有 DDL、没有 BYPASSRLS，只能读写到自己该看的数据 ──
-GRANT USAGE ON SCHEMA public TO {APP_ROLE};
-GRANT SELECT, INSERT, UPDATE, DELETE ON
-  workspace, app_user, member, invitation, audit_log TO {APP_ROLE};
-ALTER DEFAULT PRIVILEGES FOR ROLE dadao_owner IN SCHEMA public
-  GRANT SELECT, INSERT, UPDATE, DELETE ON TABLES TO {APP_ROLE};
-"""
+def _exec_each(statements: tuple[str, ...]) -> None:
+    for statement in statements:
+        op.execute(statement)
 
 
 def upgrade() -> None:
-    op.execute(HELPER_SQL)
+    _exec_each(HELPER_STATEMENTS)
 
     op.create_table(
         "app_user",
@@ -184,7 +203,7 @@ def upgrade() -> None:
     )
     op.create_index("ix_audit_ws_created", "audit_log", ["workspace_id", "created_at"])
 
-    op.execute(POLICY_SQL)
+    _exec_each(POLICY_STATEMENTS)
 
 
 def downgrade() -> None:
@@ -194,4 +213,5 @@ def downgrade() -> None:
     op.drop_table("member")
     op.drop_table("workspace")
     op.drop_table("app_user")
-    op.execute("DROP FUNCTION IF EXISTS app_ws_id(); DROP FUNCTION IF EXISTS app_user_id();")
+    op.execute("DROP FUNCTION IF EXISTS app_ws_id();")
+    op.execute("DROP FUNCTION IF EXISTS app_user_id();")