Page helpers returning SX component call strings (e.g. "(~docs-intro-content)")
were sent to the client unexpanded. Components containing Python-only helpers
like `highlight` then failed with "Undefined symbol" on the client. Now
async_eval_slot_to_sx re-parses and expands these strings server-side.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>