# Market Backend Metrics CSV Design

## Goal

Extend the existing CSV export so it includes the six backend metrics already shown in the plugin UI.

## Confirmed Decisions

- Reuse the current export flow.
- Do not add a separate backend request for CSV export.
- Read backend metrics directly from the in-memory `MarketRecord`.
- Append the six backend metrics columns after the existing CSV columns.
- Keep the existing CSV columns and ordering unchanged.
- Use these exact CSV headers:
  - `看后搜率`
  - `看后搜数`
  - `新增A3数`
  - `新增A3率`
  - `CPA3`
  - `cp_search`
- If a record has no backend metrics, export empty strings for these six columns.

## Architecture

- `src/content/market/csv-exporter.ts` remains the single place that defines CSV column layout.
- The exporter will keep current base columns and Xingtu rate columns, then append six backend metrics columns.
- No UI changes.
- No batch submission changes.
- No popup or config changes.

## Data Source

Each exported row will read from:

- existing fields:
  - `authorId`
  - `authorName`
  - `location`
  - `price21To60s`
  - `rates.singleVideoAfterSearchRate`
  - `rates.personalVideoAfterSearchRate`
- new backend metrics fields:
  - `backendMetrics.afterViewSearchRate`
  - `backendMetrics.afterViewSearchCount`
  - `backendMetrics.a3IncreaseCount`
  - `backendMetrics.newA3Rate`
  - `backendMetrics.cpa3`
  - `backendMetrics.cpSearch`

## Failure Handling

- Missing backend metrics: export blank cells
- Existing rate formatting behavior remains unchanged
- Backend loading state does not alter CSV structure; it only affects whether the cells contain values or blanks

## Testing

Add tests for:

- backend metric headers appended to CSV
- backend metric values exported correctly
- empty backend metric cells when metrics are absent
- no regression in current base/rate export behavior