Fix multi-body lambda in evaluator, rebuild sx_ref.py with router module

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>

shared/sx/evaluator.py

@@ -487,7 +487,9 @@ def _sf_lambda(expr: list, env: dict) -> Lambda:
             param_names.append(p)
         else:
             raise EvalError(f"Invalid lambda param: {p}")
-    return Lambda(param_names, expr[2], dict(env))
+    body_exprs = expr[2:]
+    body = body_exprs[0] if len(body_exprs) == 1 else [Symbol("begin")] + body_exprs
+    return Lambda(param_names, body, dict(env))
 
 
 def _sf_define(expr: list, env: dict) -> Any: