evaluator.py _sf_lambda used only expr[2] (first body expression) instead
of collecting all body expressions and wrapping in (begin ...) when multiple.
This caused multi-body lambdas to silently discard all but the first expression.
Rebuilt sx_ref.py with --spec-modules deps,router,engine,signals so the
router functions are available from the bootstrapped code. The test runner
already had _load_router_from_bootstrap() but it was falling back to the
hand-written evaluator (which has set! scoping issues) because the router
functions weren't in sx_ref.py. Now 134/134 eval+router tests pass.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>