Add cached environment manager for exec server URL (#15785)

Add environment manager that is a singleton and is created early in
app-server (before skill manager, before config loading).

Use an environment variable to point to a running exec server.

codex-rs/core/tests/common/test_codex.rs

@@ -105,8 +105,7 @@ impl TestEnv {
     pub async fn local() -> Result<Self> {
         let local_cwd_temp_dir = TempDir::new()?;
         let cwd = local_cwd_temp_dir.path().to_path_buf();
-        let environment =
-            codex_exec_server::Environment::create(/*experimental_exec_server_url*/ None).await?;
+        let environment = codex_exec_server::Environment::create(/*exec_server_url*/ None).await?;
         Ok(Self {
             environment,
             cwd,
@@ -119,8 +118,8 @@ impl TestEnv {
         &self.environment
     }
 
-    pub fn experimental_exec_server_url(&self) -> Option<&str> {
-        self.environment.experimental_exec_server_url()
+    pub fn exec_server_url(&self) -> Option<&str> {
+        self.environment.exec_server_url()
     }
 }
 
@@ -390,17 +389,17 @@ impl TestCodexBuilder {
         server: &wiremock::MockServer,
     ) -> anyhow::Result<TestCodex> {
         let test_env = test_env().await?;
-        let experimental_exec_server_url =
-            test_env.experimental_exec_server_url().map(str::to_owned);
+        let home = match self.home.clone() {
+            Some(home) => home,
+            None => Arc::new(TempDir::new()?),
+        };
+        let base_url = format!("{}/v1", server.uri());
         let cwd = test_env.cwd.to_path_buf();
         self.config_mutators.push(Box::new(move |config| {
-            config.experimental_exec_server_url = experimental_exec_server_url;
             config.cwd = cwd.abs();
         }));
-
-        let mut test = self.build(server).await?;
-        test._test_env = test_env;
-        Ok(test)
+        let (config, cwd) = self.prepare_config(base_url, &home).await?;
+        Box::pin(self.build_from_config(config, cwd, home, /*resume_from*/ None, test_env)).await
     }
 
     pub async fn build_with_streaming_server(
@@ -479,18 +478,23 @@ impl TestCodexBuilder {
         test_env: TestEnv,
     ) -> anyhow::Result<TestCodex> {
         let auth = self.auth.clone();
+        let environment_manager = Arc::new(codex_exec_server::EnvironmentManager::new(
+            test_env.exec_server_url().map(str::to_owned),
+        ));
         let thread_manager = if config.model_catalog.is_some() {
             ThreadManager::new(
                 &config,
                 codex_core::test_support::auth_manager_from_auth(auth.clone()),
                 SessionSource::Exec,
                 CollaborationModesConfig::default(),
+                Arc::clone(&environment_manager),
             )
         } else {
             codex_core::test_support::thread_manager_with_models_provider_and_home(
                 auth.clone(),
                 config.model_provider.clone(),
                 config.codex_home.clone(),
+                Arc::clone(&environment_manager),
             )
         };
         let thread_manager = Arc::new(thread_manager);