## ADDED Requirements

### Requirement: Asset Exchange Generation Trace Display

The asset information page SHALL display exchange generation relationships exclusively from `exchange_trace.previous_asset` and `exchange_trace.next_asset` returned by `GET /api/admin/assets/resolve/{identifier}`. The frontend MUST NOT infer the exchange chain from asset status, generation, exchange order status, or any field outside `exchange_trace`.

#### Scenario: Display previous asset for a replacement asset

- **GIVEN** 用户正在查看资产信息页
- **WHEN** 解析响应包含非空的 `exchange_trace.previous_asset`
- **THEN** 页面 MUST 显示“换货新资产”标签
- **AND** 页面 MUST 展示前代资产的标识符和换货单号
- **AND** 页面 MUST use `previous_asset.identifier` and `previous_asset.exchange_no` as the displayed source values

#### Scenario: Display next asset for a replaced asset

- **GIVEN** 用户正在查看资产信息页
- **WHEN** 解析响应包含非空的 `exchange_trace.next_asset`
- **THEN** 页面 MUST 显示“已换出旧资产”标签
- **AND** 页面 MUST 展示后代资产的标识符和换货单号
- **AND** 页面 MUST use `next_asset.identifier` and `next_asset.exchange_no` as the displayed source values

#### Scenario: Display both relationships for an intermediate asset

- **GIVEN** 用户正在查看位于换货链中间的资产
- **WHEN** 解析响应同时包含非空的 `previous_asset` 和 `next_asset`
- **THEN** 页面 MUST 同时展示“换货新资产”和“已换出旧资产”两个关联区域
- **AND** 两个区域 MUST use their corresponding relationship item values independently

#### Scenario: Hide absent exchange relationship

- **GIVEN** 用户正在查看资产信息页
- **WHEN** `previous_asset` 或 `next_asset` 为 `null`、空值或未返回
- **THEN** 页面 MUST NOT 展示对应的换货关联区域
- **AND** 前端 MUST NOT 根据资产状态、世代编号、换货单状态或其他字段推导该区域

#### Scenario: Display no exchange relationship for unrelated asset

- **GIVEN** 用户正在查看无前代和后代换货关系的资产
- **WHEN** 解析响应未返回 `exchange_trace` 或 `exchange_trace` 内两个关联项均为空
- **THEN** 页面 MUST NOT 展示“换货新资产”标签
- **AND** 页面 MUST NOT 展示“已换出旧资产”标签
- **AND** 页面 MUST NOT render an empty exchange relationship placeholder

### Requirement: Exchange Related Asset Navigation Authorization

The asset information page SHALL allow navigation to a related exchange asset only when that relationship item has `can_view=true`. When `can_view=false`, the relationship item SHALL remain visible as text only and MUST NOT provide any asset-detail navigation affordance.

#### Scenario: Navigate to authorized related asset

- **GIVEN** 换货关联资产项的 `can_view=true`
- **WHEN** 用户点击关联资产标识符
- **THEN** 系统 MUST 跳转到该关联资产的资产详情
- **AND** 跳转 MUST 使用关联项返回的 `identifier`
- **AND** 页面 MUST NOT reconstruct the target identifier from the current asset or exchange order

#### Scenario: Render unauthorized related asset as text

- **GIVEN** 换货关联资产项的 `can_view=false`
- **WHEN** 页面渲染换货关联区域
- **THEN** 页面 MUST 展示关联资产标识符和换货单号
- **AND** 页面 MUST NOT 将关联资产标识符渲染为可点击跳转操作

#### Scenario: Render nullable related asset ID without navigation

- **GIVEN** 换货关联资产项的 `asset_id=null`
- **AND** 该关联资产项的 `can_view=false`
- **WHEN** 页面渲染换货关联区域
- **THEN** 页面 MUST 展示关联资产标识符和换货单号
- **AND** 页面 MUST NOT depend on `asset_id` to render the relationship text
- **AND** 页面 MUST NOT provide navigation to the related asset

### Requirement: Exchange Trace Response Contract

The frontend asset resolve contract SHALL support optional `exchange_trace.previous_asset` and `exchange_trace.next_asset` returned by `GET /api/admin/assets/resolve/{identifier}`. Each non-empty relationship item SHALL preserve `asset_type:string`, `asset_id:int64|null`, `identifier:string`, `exchange_no:string`, and `can_view:bool`.

#### Scenario: Read exchange trace response fields

- **WHEN** 前端解析 `GET /api/admin/assets/resolve/{identifier}` 响应
- **THEN** 前端类型 MUST 支持 `exchange_trace.previous_asset` 和 `exchange_trace.next_asset`
- **AND** 每个非空关联项 MUST 支持读取 `asset_type`、`asset_id`、`identifier`、`exchange_no`、`can_view`
- **AND** `asset_id` MUST allow `null` for no-permission relationship items
- **AND** `previous_asset` and `next_asset` MUST each allow `null`, empty, or omitted values

#### Scenario: Preserve asset type in exchange trace item

- **WHEN** 解析响应返回 `exchange_trace.previous_asset` 或 `exchange_trace.next_asset`
- **THEN** 前端类型 MUST preserve `asset_type` as a string value such as `device` or `card`
- **AND** 页面 logic MUST NOT assume all related exchange assets are the same type as the current asset
