Enforce Agent Plugin runtime boundaries (#37027)

## What changed

- Track Agent Plugin manifests through plugin, skill, and MCP loading so their capabilities use format-specific behavior without changing legacy plugins.
- Discover only direct-child skills, exclude app and hook capabilities, isolate MCP data, and reject MCP configuration files that are non-regular or resolve outside the plugin root.
- Bound model-visible skill instructions, plugin instructions, MCP descriptions, schemas, individual tools, and the aggregate Agent Plugin MCP tool set.
- Stop MCP and OAuth redirects when Agent Plugins send configured or authorization headers, while retaining existing redirect behavior for legacy MCP servers.

## Testing

- Add coverage for capability filtering, skill discovery, isolated MCP data and reserved-path expansion, unsafe MCP configuration files, context limits, and redirect handling.

GitOrigin-RevId: c9af66b051269f3226628ca280a58d32c808c38f

codex-rs/rmcp-client/src/lib.rs

@@ -24,6 +24,7 @@ pub use auth_status::determine_streamable_http_auth_status;
 pub use auth_status::determine_streamable_http_auth_status_from_credentials;
 pub use auth_status::discover_streamable_http_oauth;
 pub use codex_protocol::protocol::McpAuthStatus;
+pub use http_client_adapter::StreamableHttpRedirectMode;
 pub use in_process_transport::InProcessTransportFactory;
 pub use oauth::StoredOAuthTokens;
 pub use oauth::WrappedOAuthTokenResponse;