Fix remaining test runners for CEK-default mode: override to tree-walk

run_type_tests.py, run_signal_tests.py, run_continuation_tests.py all
needed the same sx_ref.eval_expr/trampoline override to tree-walk that
was applied to the CEK test runners. Without this, transpiled HO forms
(ho_map, etc.) re-entered CEK mid-evaluation causing "Unknown frame
type: map" errors. All 186 tests now pass across 5 suites.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/run_continuation_tests.py

@@ -35,8 +35,13 @@ finally:
 from shared.sx.parser import parse_all
 from shared.sx.types import NIL
 
-eval_expr = mod.eval_expr
-trampoline = mod.trampoline
+# Use tree-walk evaluator for interpreting .sx test files.
+# CEK is now the default, but test runners need tree-walk so that
+# transpiled HO forms (ho_map, etc.) don't re-enter CEK mid-evaluation.
+eval_expr = mod._tree_walk_eval_expr
+trampoline = mod._tree_walk_trampoline
+mod.eval_expr = eval_expr
+mod.trampoline = trampoline
 env = mod.make_env()
 
 # Platform test functions