Fall back to http when websockets fail (#10139)

I expect not all proxies work with websockets, fall back to http if
websockets fail.

codex-rs/core/tests/suite/websocket_fallback.rs

@@ -0,0 +1,98 @@
+use anyhow::Result;
+use codex_core::WireApi;
+use core_test_support::responses;
+use core_test_support::responses::ev_completed;
+use core_test_support::responses::ev_response_created;
+use core_test_support::responses::mount_sse_once;
+use core_test_support::responses::mount_sse_sequence;
+use core_test_support::responses::sse;
+use core_test_support::skip_if_no_network;
+use core_test_support::test_codex::test_codex;
+use pretty_assertions::assert_eq;
+use wiremock::http::Method;
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn websocket_fallback_switches_to_http_after_retries_exhausted() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let response_mock = mount_sse_once(
+        &server,
+        sse(vec![ev_response_created("resp-1"), ev_completed("resp-1")]),
+    )
+    .await;
+
+    let mut builder = test_codex().with_config({
+        let base_url = format!("{}/v1", server.uri());
+        move |config| {
+            config.model_provider.base_url = Some(base_url);
+            config.model_provider.wire_api = WireApi::ResponsesWebsocket;
+            config.model_provider.stream_max_retries = Some(0);
+            config.model_provider.request_max_retries = Some(0);
+        }
+    });
+    let test = builder.build(&server).await?;
+
+    test.submit_turn("hello").await?;
+
+    let requests = server.received_requests().await.unwrap_or_default();
+    let websocket_attempts = requests
+        .iter()
+        .filter(|req| req.method == Method::GET && req.url.path().ends_with("/responses"))
+        .count();
+    let http_attempts = requests
+        .iter()
+        .filter(|req| req.method == Method::POST && req.url.path().ends_with("/responses"))
+        .count();
+
+    assert_eq!(websocket_attempts, 1);
+    assert_eq!(http_attempts, 1);
+    assert_eq!(response_mock.requests().len(), 1);
+
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn websocket_fallback_is_sticky_across_turns() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let response_mock = mount_sse_sequence(
+        &server,
+        vec![
+            sse(vec![ev_response_created("resp-1"), ev_completed("resp-1")]),
+            sse(vec![ev_response_created("resp-2"), ev_completed("resp-2")]),
+        ],
+    )
+    .await;
+
+    let mut builder = test_codex().with_config({
+        let base_url = format!("{}/v1", server.uri());
+        move |config| {
+            config.model_provider.base_url = Some(base_url);
+            config.model_provider.wire_api = WireApi::ResponsesWebsocket;
+            config.model_provider.stream_max_retries = Some(0);
+            config.model_provider.request_max_retries = Some(0);
+        }
+    });
+    let test = builder.build(&server).await?;
+
+    test.submit_turn("first").await?;
+    test.submit_turn("second").await?;
+
+    let requests = server.received_requests().await.unwrap_or_default();
+    let websocket_attempts = requests
+        .iter()
+        .filter(|req| req.method == Method::GET && req.url.path().ends_with("/responses"))
+        .count();
+    let http_attempts = requests
+        .iter()
+        .filter(|req| req.method == Method::POST && req.url.path().ends_with("/responses"))
+        .count();
+
+    assert_eq!(websocket_attempts, 1);
+    assert_eq!(http_attempts, 2);
+    assert_eq!(response_mock.requests().len(), 2);
+
+    Ok(())
+}