Fix relative stdio MCP cwd fallback (#19031)

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

@@ -618,6 +618,69 @@ async fn remote_stdio_server_uses_runtime_fallback_cwd_when_config_omits_cwd() -
     Ok(())
 }
 
+#[cfg(unix)]
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+#[serial(mcp_cwd)]
+async fn local_stdio_server_uses_runtime_fallback_cwd_when_config_omits_cwd() -> anyhow::Result<()>
+{
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let server_name = "rmcp_local_fallback_cwd";
+    let expected_cwd = Arc::new(Mutex::new(None::<PathBuf>));
+    let expected_cwd_for_config = Arc::clone(&expected_cwd);
+    let rmcp_test_server_bin = cargo_bin("test_stdio_server")?;
+    let relative_server_path = PathBuf::from("mcp-bin").join(
+        rmcp_test_server_bin
+            .file_name()
+            .expect("test stdio server binary should have a file name"),
+    );
+    let relative_command = relative_server_path.to_string_lossy().into_owned();
+
+    let fixture = test_codex()
+        .with_config(move |config| {
+            *expected_cwd_for_config
+                .lock()
+                .expect("expected cwd lock should not be poisoned") =
+                Some(config.cwd.to_path_buf());
+
+            let target_bin = config.cwd.join(&relative_server_path).into_path_buf();
+            let target_dir = target_bin
+                .parent()
+                .expect("relative test server path should include a parent");
+            fs::create_dir_all(target_dir).expect("create relative MCP bin directory");
+            fs::copy(&rmcp_test_server_bin, &target_bin).expect("copy test stdio server");
+
+            insert_mcp_server(
+                config,
+                server_name,
+                stdio_transport(
+                    relative_command,
+                    Some(HashMap::from([(
+                        "MCP_TEST_VALUE".to_string(),
+                        "local-fallback-cwd".to_string(),
+                    )])),
+                    Vec::new(),
+                ),
+                TestMcpServerOptions::default(),
+            );
+        })
+        .build(&server)
+        .await?;
+
+    let expected_cwd = expected_cwd
+        .lock()
+        .expect("expected cwd lock should not be poisoned")
+        .clone()
+        .expect("test config should record runtime fallback cwd");
+    let structured =
+        call_cwd_tool(&server, &fixture, server_name, "call-local-fallback-cwd").await?;
+
+    assert_cwd_tool_output(&structured, &expected_cwd);
+    server.verify().await;
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
 async fn stdio_mcp_tool_call_includes_sandbox_state_meta() -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));