Make local environment optional in EnvironmentManager (#23369)

## Summary
- make `EnvironmentManager` local environment/runtime paths optional
- simplify constructor surface around snapshot materialization
- rename local env accessors to `require_local_environment` /
`try_local_environment`

## Validation
- devbox Bazel build for touched crate surfaces
- `//codex-rs/exec-server:exec-server-unit-tests`
- `//codex-rs/app-server-client:app-server-client-unit-tests`
- filtered touched `//codex-rs/core:core-unit-tests` cases

codex-rs/core/src/connectors.rs

@@ -198,7 +198,8 @@ pub async fn list_accessible_connectors_from_mcp_tools_with_options_and_status(
         config.codex_linux_sandbox_exe.clone(),
     )?;
     let environment_manager =
-        EnvironmentManager::from_codex_home(config.codex_home.clone(), local_runtime_paths).await?;
+        EnvironmentManager::from_codex_home(config.codex_home.clone(), Some(local_runtime_paths))
+            .await?;
     list_accessible_connectors_from_mcp_tools_with_environment_manager(
         config,
         force_refetch,
@@ -261,10 +262,6 @@ pub async fn list_accessible_connectors_from_mcp_tools_with_environment_manager(
     let (tx_event, rx_event) = unbounded();
     drop(rx_event);
 
-    let environment = environment_manager
-        .default_environment()
-        .unwrap_or_else(|| environment_manager.local_environment());
-
     let (mut mcp_connection_manager, cancel_token) = McpConnectionManager::new(
         &mcp_servers,
         config.mcp_oauth_credentials_store_mode,
@@ -273,7 +270,13 @@ pub async fn list_accessible_connectors_from_mcp_tools_with_environment_manager(
         INITIAL_SUBMIT_ID.to_owned(),
         tx_event,
         PermissionProfile::default(),
-        McpRuntimeEnvironment::new(environment, config.cwd.to_path_buf()),
+        // Connector discovery is threadless. Use an actually configured env if
+        // one exists, but do not reintroduce the old hidden-local fallback.
+        McpRuntimeEnvironment::new(
+            environment_manager.default_or_local_environment(),
+            environment_manager.try_local_environment(),
+            config.cwd.to_path_buf(),
+        ),
         config.codex_home.to_path_buf(),
         codex_apps_tools_cache_key(auth.as_ref()),
         host_owned_codex_apps_enabled,