build: add response time header

backend-rewrite-tasklist/01_M0_M2_FOUNDATION_AND_AUTH.md

@@ -108,7 +108,8 @@
   交付物：[../server-rs/apps/api-server/src/response_headers.rs](../server-rs/apps/api-server/src/response_headers.rs)
 - [x] 接入 `x-route-version`
   交付物：[../server-rs/apps/api-server/src/response_headers.rs](../server-rs/apps/api-server/src/response_headers.rs)
-- [ ] 接入 `x-response-time-ms`
+- [x] 接入 `x-response-time-ms`
+  交付物：[../server-rs/apps/api-server/src/response_headers.rs](../server-rs/apps/api-server/src/response_headers.rs)、[../server-rs/apps/api-server/src/request_context.rs](../server-rs/apps/api-server/src/request_context.rs)
 - [ ] 实现 `/healthz`
 
 ### 基础工程脚本

server-rs/apps/api-server/README.md

@@ -62,7 +62,7 @@
 1. 所有响应都会回写 `x-request-id`。
 2. 所有响应都会回写固定的 `x-api-version`，当前值与 body `meta.apiVersion` 保持一致。
 3. 所有响应都会回写 `x-route-version`，当前阶段默认与 `x-api-version` 保持一致，后续再按路由粒度细分。
-4. `x-response-time-ms` 仍留在后续独立任务中补齐。
+4. 所有响应都会回写 `x-response-time-ms`，值来源于 `RequestContext` 内记录的请求开始时间。
 
 ## 3. 边界约束
 

server-rs/apps/api-server/src/response_headers.rs

@@ -7,14 +7,16 @@ use axum::{
 
 use crate::{
     api_response::API_VERSION,
-    request_context::{resolve_request_id, X_REQUEST_ID_HEADER},
+    request_context::{resolve_request_id, RequestContext, X_REQUEST_ID_HEADER},
 };
 
 pub const API_VERSION_HEADER: &str = "x-api-version";
+pub const RESPONSE_TIME_HEADER: &str = "x-response-time-ms";
 pub const ROUTE_VERSION_HEADER: &str = "x-route-version";
 
 pub async fn propagate_request_id_header(request: Request, next: Next) -> Response {
     let request_id = resolve_request_id(&request);
+    let request_context = request.extensions().get::<RequestContext>().cloned();
     let mut response = next.run(request).await;
 
     if let Some(request_id) = request_id {
@@ -37,5 +39,13 @@ pub async fn propagate_request_id_header(request: Request, next: Next) -> Respon
             .insert(HeaderName::from_static(ROUTE_VERSION_HEADER), header_value);
     }
 
+    if let Some(request_context) = request_context {
+        if let Ok(header_value) = HeaderValue::from_str(&request_context.elapsed().to_string()) {
+            response
+                .headers_mut()
+                .insert(HeaderName::from_static(RESPONSE_TIME_HEADER), header_value);
+        }
+    }
+
     response
 }