Port cstage cmd/wcc/check.c:870-894 to exprtype. indexresult yields
the resolved element tnode for slice/array, u8 for str, T for *[N]T
(decay) and *T (generic), and []T for *[]T (no decay, mirrors the
Hare-faithful rule at check.c:883-885). The arm stamps e.type_ via
tinfofornode same shape as the A.6.1.3 BIN/UN pattern.
Phase 1 A.6 step 4 of 6 — slot the indexing result type into the
mandatory post-checker invariant. Cgenutil still derives index
stride from AST shape (indexbaseesz, elemsizeofc, indexvaluetnode);
A.6.3 will collapse those onto the now-stamped N_INDEX type_.
Verified 132/132 incl. 995_self_rebuild byte-identity.
Hojun-Cho
0715ec9662