cstage rejects `add(1,2,3)` and `add(4)` (too many / not enough
arguments); wwstage ran no count check at this seam, so both built
-- a stray arg pushed silently, a missing one read garbage
(cs-reject/ww-accept build-verdict divergence). Surplus errs when
params exhaust with args left; missing errs on a leftover regular
param (a leftover TK_ELLIPSIS or FFI "..." is a legal zero-arg
variadic tail). fn-VALUE callees still bail at decl==nil -- their
whole typecheck, arity included, stays task #51.
Hojun-Cho
503d1ab01e