checker: a function named like a built-in a call always takes is refused at its declaration - function words(st, k) compiled and every call became words(n) with a pointer for n (invalid IR, far from the cause); the table is selfhost/check/check_builtins.ludic, emit_call's built-ins no find_fn guard lets a declared function take, and ludic-dev syntax --check holds it to emit_call both ways; every other built-in (buffer, floats, double, ...) yields to a declared function in the checker as it already did in codegen. string_temps' keep and cross_heap_test's keep renamed (hand, keep_cell); rejected/builtin_call_name and functions/builtin_yield with their cases (added, not run); reseeded, bootstrap-cfree fixpoint holds

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/rejected/builtin_call_name.ludic

@@ -0,0 +1,8 @@
+# builtin_call_name.ludic - a function named like a built-in a call always takes is refused at its
+# declaration: every call to `words` is words(n), n zeroed ints, so this helper would never run (a
+# pointer became its size). (Rejected on purpose: tools/ludic-cli/test.ludic.)
+program BuiltinCallName {
+  function words(n: int, k: string) -> string { return k }
+  function keep(s: string) -> string { return s }
+  entry { print(words(1, keep("x"))) }
+}