The closure merging in jit_compile_lambda (copying globals + injecting
closure bindings into vm_env_ref) produces incorrect variable resolution
for inner functions. Symptoms: sx-parse's read-list-loop mishandles
closing parens (siblings become children), parser produces wrong ASTs.
Fix: vm_call skips JIT compilation for lambdas with non-empty closures.
These run on CEK which handles closures correctly. Top-level defines
(empty closure) are still JIT-compiled.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>