The ~component check in _aser immediately serialized all names starting
with ~ as unexpanded component calls. This meant defmacro definitions
like ~root-header-auto were sent to the client unexpanded, causing
"Undefined symbol: root-header-ctx" errors since IO primitives only
exist server-side. Now checks env for Macro instances first.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>