# T774 — product match race metering regression

> Status: `todo`  
> Milestone: `M7` · Phase D  
> Kind: `test` · Est. change: `~190 lines`

## Goal

證明多 worker／重試不重複 ProductMatch 或 AI 計費，Sweep counters 與實際資料可對帳。

## Depends on

- T770–T773

## Inputs

- radar worker/sweep/repository/usage fake harness
- `../spec.md` §4.2、§5.5、§8、驗收 #12

## Outputs

| 路徑 | 動作 | 說明 |
|------|------|------|
| `apps/backend/internal/module/radar/usecase/product_race_meter_test.go` | add | same/different product worker race、retry |
| `apps/backend/internal/module/radar/usecase/sweep_counter_test.go` | edit/add | evaluated/merged/rejected/truncated reconciliation |
| usage integration tests | edit | `radar.product_fit` exactly-once semantics |

## Behavior

- 同 `(opportunity, product)` 最多一次適配計費。
- 不同 Product 可各計一次但仍一 Opportunity。
- job guarded update、Redis lock value=workerID 規則不變。

## Out of scope

- 真 AI／Threads 網路壓測
- 新 usage meter

## Acceptance

- [ ] race detector 綠，資料筆數／counter／usage records 對帳。

```bash
cd apps/backend && go test ./internal/module/radar/... ./internal/module/usage/... -race -count=1
```