Extend runtime auth to account, plugin, and file requests (#59564)

## What changed

- Use the shared runtime and effective configuration for account API clients and remote plugin requests, including standalone plugin commands.
- Support dual-header and assertion-only authentication for remote plugins and MCP file uploads when runtime agent instances are enabled.
- Keep plugin credentials and caches scoped to the thread's account when resuming with different credentials. Bind request pools and multi-step plugin storage operations to the selected account so account replacement revokes stale operations.
- Protect runtime credentials on cross-origin redirects while preserving configured routing policies and legacy authentication for custom backends.
- Apply server-provided `upload_headers` to file storage uploads.

## Testing

Add coverage for shared runtime registration, both authentication modes, configuration reloads, resumed-thread account selection, account replacement during plugin uploads and downloads, and credential stripping on redirects. Extend file upload tests to verify runtime assertions and storage-only upload headers.

GitOrigin-RevId: 68aef81051a6f9bf919fffda52f372b108fce805

codex-rs/cli/src/mcp_cmd.rs

@@ -19,7 +19,7 @@ use codex_core::config::LoaderOverrides;
 use codex_core::config::edit::ConfigEditsBuilder;
 use codex_core::config::find_codex_home;
 use codex_core::config::load_global_mcp_servers;
-use codex_core::plugins_manager_for_config;
+use codex_core::plugins_manager_for_config_with_runtime;
 use codex_exec_server::EnvironmentManager;
 use codex_exec_server::HttpClient;
 use codex_exec_server::RouteAwareHttpClient;
@@ -533,10 +533,10 @@ async fn run_remove(config_overrides: &CliConfigOverrides, remove_args: RemoveAr
 }
 
 async fn load_mcp_manager(config: &Config) -> Result<McpManager> {
-    let plugins_manager = Arc::new(plugins_manager_for_config(
-        config,
-        load_cli_auth_manager(config).await?,
-    ));
+    let plugins_manager = Arc::new(
+        plugins_manager_for_config_with_runtime(config, load_cli_auth_manager(config).await?)
+            .await?,
+    );
     Ok(McpManager::new(plugins_manager))
 }