Add service name to the header

service/src/main/kotlin/app/cash/backfila/client/EnvoyCallbackConnectorProvider.kt

@@ -58,11 +58,12 @@ class EnvoyCallbackConnectorProvider @Inject constructor(
     val httpClientEndpointConfig = httpClientsConfig[baseUrl]
 
     var okHttpClient = httpClientFactory.create(httpClientEndpointConfig)
+    val okHttpClientBuilder = okHttpClient.newBuilder()
+    okHttpClientBuilder.addInterceptor(ServiceNameHeaderInterceptor(serviceName))
     if (!headers.isNullOrEmpty()) {
-      okHttpClient = okHttpClient.newBuilder()
-        .addInterceptor(OkHttpClientSpecifiedHeadersInterceptor(headers))
-        .build()
+      okHttpClientBuilder.addInterceptor(OkHttpClientSpecifiedHeadersInterceptor(headers))
     }
+    okHttpClient = okHttpClientBuilder.build()
 
     val retrofit = Retrofit.Builder()
       .baseUrl(baseUrl)

service/src/main/kotlin/app/cash/backfila/client/GrpcCallbackConnectorProvider.kt

@@ -53,6 +53,8 @@ class GrpcCallbackConnectorProvider @Inject constructor(
     val baseUrl = httpClientConfigUrlProvider.getUrl(httpClientEndpointConfig)
 
     val okHttpClientBuilder = httpClientFactory.create(httpClientEndpointConfig).newBuilder()
+
+    okHttpClientBuilder.addInterceptor(ServiceNameHeaderInterceptor(serviceName))
     if (!headers.isNullOrEmpty()) {
       okHttpClientBuilder.addInterceptor(OkHttpClientSpecifiedHeadersInterceptor(headers))
     }

service/src/main/kotlin/app/cash/backfila/client/HttpCallbackConnectorProvider.kt

@@ -57,6 +57,7 @@ class HttpCallbackConnectorProvider @Inject constructor(
           addNetworkInterceptor(it)
         }
       }
+    okHttpClientBuilder.addInterceptor(ServiceNameHeaderInterceptor(serviceName))
     if (!headers.isNullOrEmpty()) {
       okHttpClientBuilder.addInterceptor(OkHttpClientSpecifiedHeadersInterceptor(headers))
     }

service/src/main/kotlin/app/cash/backfila/client/ServiceNameHeaderInterceptor.kt

@@ -0,0 +1,21 @@
+package app.cash.backfila.client
+
+import okhttp3.Interceptor
+import okhttp3.Response
+
+/**
+ * Adds service name header to HTTP requests for service identification.
+ * This allows downstream systems to identify which service made the request.
+ */
+class ServiceNameHeaderInterceptor(
+  private val serviceName: String,
+) : Interceptor {
+  override fun intercept(chain: Interceptor.Chain): Response {
+    val request = chain.request()
+      .newBuilder()
+      .header("X-Forwarded-Service", serviceName)
+      .build()
+
+    return chain.proceed(request)
+  }
+}