fix(cost): 历史订单成本固化，只有预估→实际允许升级

- 已有快照不再因成本版本变更而替换，历史订单成交价与成本保持固定
- 仅接单平台「预估 → 实际」履约结算允许 supersede
- 补配价格只影响没有快照的订单；文档同步口径

apps/backend/src/services/cost-center/cost-snapshot-service.test.ts

@@ -3,6 +3,7 @@ import test from 'node:test'
 
 import {
   resolveCost,
+  shouldSupersedeSnapshot,
   resolveGenericCosts,
   selectCostVersion,
   type CostItemRow,
@@ -354,3 +355,11 @@ test('比例费用按退款后的净收入计算', () => {
   assert.equal(noRefund[0]?.totalAmountFen, 300)
   assert.equal(withRefund[0]?.totalAmountFen, 180)
 })
+
+test('历史订单成本固化：只有预估→实际允许替换', () => {
+  assert.equal(shouldSupersedeSnapshot(null, 'estimated'), true)
+  assert.equal(shouldSupersedeSnapshot('estimated', 'estimated'), false)
+  assert.equal(shouldSupersedeSnapshot('estimated', 'actual'), true)
+  assert.equal(shouldSupersedeSnapshot('actual', 'estimated'), false)
+  assert.equal(shouldSupersedeSnapshot('actual', 'actual'), false)
+})

apps/backend/src/services/cost-center/cost-snapshot-service.ts

@@ -243,6 +243,18 @@ export function resolveGenericCosts(
   return result
 }
 
+/**
+ * 历史订单成本固化：已有快照不再因成本版本变更而替换。
+ * 唯一允许的变化是「预估 → 实际」的履约结算升级。
+ */
+export function shouldSupersedeSnapshot(
+  currentStage: string | null | undefined,
+  nextStage: string,
+): boolean {
+  if (!currentStage) return true
+  return currentStage !== 'actual' && nextStage === 'actual'
+}
+
 export type SyncCostSnapshotsResult = {
   scanned: number
   created: number
@@ -351,6 +363,8 @@ export async function syncChannelCostSnapshots(
           continue
         }
         if (current) {
+          // 历史订单成本/成交价已固化，只有「预估→实际」允许升级。
+          if (!shouldSupersedeSnapshot(current.snapshot_stage, resolution.stage)) continue
           supersedeIds.push(Number(current.id))
           result.superseded += 1
         }