`case T1 | T2 =>` (binding-less; cstage parse.c:635-650 chains extra
types through cs->list, bindings stay single-type by design). Three
wwstage layers, no AST change (node.list already exists):
- parser (expr.ww): pipe loop after the non-let arm's first
parsetype;
- checker (check.ww): resolvewalk N_MCASE now walks n.list so each
alt gets its type_ stamp (exhaustiveness/casecovers were already
alt-aware, built ahead of the parser);
- cgen (cgenexpr.ww): the single-pattern want-computation moves
VERBATIM into matcharmwant; a cs.list arm emits CMPQ/JE per alt
funneling into one match_body label, mirroring cgen.c:11118-11141
incl. label mint order and the tag<0 clamp. Nullable arms keep
ignoring alts (both stages).
Graduates the held e2e row (pin 1732/1158/3464); byte-identical on
the repro and the single-pattern control.
Hojun-Cho
184afa3243