evaluator.sx defines *custom-special-forms* and register-special-form!
which shadow the host's native bindings when loaded at runtime. The
native bindings route to Sx_ref.custom_special_forms (the dict the CEK
evaluator checks), but the SX-level defines create a separate dict.
Fix: rebind_host_extensions runs after every load command, re-asserting
the native register-special-form! and *custom-special-forms* bindings.
Add regression test: custom form registered before evaluator.sx load
survives and remains callable via CEK dispatch afterward.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
3ae49b69f5