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/core/src/tools/handlers/request_plugin_install.rs

@@ -191,7 +191,10 @@ impl RequestPluginInstallHandler {
             let auth = session.services.auth_manager.auth().await;
             let plugins_config = turn.config.plugins_config_input();
             match codex_core_plugins::hydrate_selected_recommended_plugin_install_metadata(
-                &plugins_config,
+                &session
+                    .services
+                    .plugins_manager
+                    .remote_plugin_service_config(&plugins_config),
                 auth.as_ref(),
                 tool,
             )