feat(allocation): 二次分配方案录入/替换/终态门槛（分摊计算待澄清另批）

- SecondaryAllocationIn/Out：比例走金额红线口径（str 入参、两位小数、
  超 100 拒绝不静默舍入）；参与人 schema 层去重（uk 前置友好提示）
- create/update 同事务写入（replace_allocations，先删后 flush 再插——
  uk 表防御写法）；create 放编号重试循环内，rollback 后方案随业务重来
- 人员在职复用 ensure_active（label=分摊参与），personnel_name 冗余固化；
  FK RESTRICT：被方案引用人员禁删，方案回显不静默失联
- 合计不强制 100%（需求原文）：详情 allocation_hint 只展示合计/余额，
  余额归属待澄清 #2 不落库
- 单测 13 例（比例边界/去重）+ 集成 9 例（回显/替换清空/离职 400/
  终态禁改/RESTRICT 保护）

Co-Authored-By: Claude Code <noreply@anthropic.com>

backend/app/services/business_service.py

@@ -41,6 +41,7 @@ from app.models import (
     OwnershipChangeLog,
     Personnel,
     Receipt,
+    SecondaryAllocation,
     Shipment,
     User,
 )
@@ -65,6 +66,8 @@ from app.schemas.business import (
     GrossProfitOut,
     GrossProfitRowOut,
     OwnershipChangeLogOut,
+    SecondaryAllocationIn,
+    SecondaryAllocationOut,
 )
 from app.services import audit_service, param_service, personnel_service
 from app.services.audit_service import AuditRecord, RequestMeta
@@ -257,7 +260,7 @@ def list_businesses(session: Session, query: BusinessQuery) -> PageResult[Busine
 
 
 def get_detail(session: Session, business_id: int) -> BusinessDetailOut:
-    """业务详情（附明细行，供编辑抽屉回显）。
+    """业务详情（附明细行与二次分配方案，供编辑抽屉回显）。
 
     :raises NotFoundError: 业务不存在
     """
@@ -268,9 +271,53 @@ def get_detail(session: Session, business_id: int) -> BusinessDetailOut:
     out.items = [
         _item_to_out(item) for item in business_repository.list_items(session, business_id)
     ]
+    allocations = business_repository.list_allocations(session, business_id)
+    out.secondary_allocations = [
+        SecondaryAllocationOut(
+            personnel_id=a.personnel_id, personnel_name=a.personnel_name, ratio=str(a.ratio)
+        )
+        for a in allocations
+    ]
+    out.allocation_hint = _allocation_hint(allocations)
     return out
 
 
+def _build_allocation_rows(
+    session: Session, business_id: int, items: list[SecondaryAllocationIn]
+) -> list[SecondaryAllocation]:
+    """构造二次分配明细行：人员在职校验 + 姓名冗余固化 + 比例转 Decimal。
+
+    :raises BadRequestError: 参与人员不存在或已离职
+    """
+    rows: list[SecondaryAllocation] = []
+    for item in items:
+        person = _ensure_personnel_active(session, item.personnel_id, "分摊参与")
+        rows.append(
+            SecondaryAllocation(
+                business_id=business_id,
+                personnel_id=item.personnel_id,
+                personnel_name=person.personnel_name,
+                ratio=Decimal(item.ratio),
+            )
+        )
+    return rows
+
+
+def _allocation_hint(allocations: list[SecondaryAllocation]) -> str | None:
+    """方案合计/余额提示（不强制合计满额是需求原文；余额归属待澄清 #2）。
+
+    无方案返回 None；合计恰满额只报合计，避免「余额 0」噪音。
+    """
+    if not allocations:
+        return None
+    total = sum((a.ratio for a in allocations), Decimal("0"))
+    total_text = total.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP)
+    if total == Decimal("100"):
+        return f"二次分配合计 {total_text}%"
+    rest = (Decimal("100") - total).quantize(Decimal("0.01"), rounding=ROUND_HALF_UP)
+    return f"二次分配合计 {total_text}%，余额 {rest}%（归属待业务确认）"
+
+
 def create_business(
     session: Session,
     payload: BusinessCreateIn,
@@ -335,6 +382,13 @@ def create_business(
                         operator_name=operator.username,
                     ),
                 )
+                # 二次分配方案与业务同事务（需求：只出现在合同刚建立时）；
+                # 放在重试循环内——rollback 后方案行随业务一并重来
+                business_repository.replace_allocations(
+                    session,
+                    business.id,
+                    _build_allocation_rows(session, business.id, payload.secondary_allocations),
+                )
                 customer = customer_repository.get_by_id(session, business.customer_id)
                 out = _to_out((business, customer.company_name if customer else None, None, None))
                 new_id, new_no = business.id, business.business_no  # 固化：commit 后不碰 ORM
@@ -408,6 +462,13 @@ def update_business(
         business_repository.replace_items(
             session, business_id, _build_item_rows(business_id, payload.items)
         )
+        # 方案全量替换（空数组=清空）；终态门槛已挡「修改影响已结算月份」的
+        # 前置场景（月结在 ④，快照固化后按同一哲学隔离）
+        business_repository.replace_allocations(
+            session,
+            business_id,
+            _build_allocation_rows(session, business_id, payload.secondary_allocations),
+        )
         _recalc_totals(session, business)
         # 锁定行上已赋值，同一身份映射实例的 _to_out 即反映新值；名称字段
         # 从首查 row 取（换客户时 _ensure_customer 已给出新公司名）