Strengthen publisher fallback route test

Author: ChristianPavilonis

crates/trusted-server-adapter-fastly/src/route_tests.rs

@@ -694,16 +694,52 @@ fn static_tsjs_route_returns_not_found_for_unknown_tsjs_bundle() {
 
 #[test]
 fn unknown_route_falls_back_to_publisher_proxy_path() {
-    let mut settings = create_test_settings();
-    settings.publisher.origin_url = "https://publisher-origin.invalid".to_string();
+    let settings = create_test_settings();
+    let (orchestrator, integration_registry) = build_route_stack(&settings);
+
     let req = Request::get("https://test.com/articles/example");
+    let http_client = Arc::new(RecordingHttpClient::new(StatusCode::BAD_GATEWAY));
+    let services = test_runtime_services_with_http_client(
+        &req,
+        Arc::new(FixedBackend),
+        Arc::clone(&http_client) as Arc<dyn PlatformHttpClient>,
+    );
 
-    let response = route_with_settings(&settings, req, "should route publisher fallback");
+    let response = route_buffered_response(
+        &settings,
+        &orchestrator,
+        &integration_registry,
+        &services,
+        req,
+        "should route publisher fallback",
+    );
 
     assert_eq!(
         response.get_status(),
         StatusCode::BAD_GATEWAY,
-        "should reach publisher proxy fallback and fail as an origin proxy error"
+        "should return the publisher origin response through fallback routing"
+    );
+    let calls = http_client
+        .calls
+        .lock()
+        .expect("should lock recorded calls");
+    assert_eq!(
+        calls.len(),
+        1,
+        "should send exactly one publisher fallback request"
+    );
+    assert_eq!(
+        calls[0].method,
+        Method::GET,
+        "should preserve the fallback request method"
+    );
+    assert_eq!(
+        calls[0].backend_name, "https-origin.test-publisher.com",
+        "should dispatch to the publisher origin backend"
+    );
+    assert_eq!(
+        calls[0].uri, "https://origin.test-publisher.com/articles/example",
+        "should send the fallback request to the publisher origin"
     );
 }