Hojun-Cho
4f3967835e
A tagged-union RETURN rides a fixed AX(tag)+DX/CX/R8 cursor (TUPLE_GPCAP eightbytes = 32B slot); wider slots were silently truncated at the return crossing — payload word 4+ built in the callee frame and died there, byte-identical on both stages (gate-blind). Blocks regex fold-2a ((regex | error | nomem) = 64B slot). Classifier: cg_sret_retsize / sretretsize gain a TY_TAGGED arm (<= TUPLE_GPCAP*8 stays register-ABI — the (str|nomem)/(s3|bool) 32B boundary class is pinned unchanged byte-for-byte vs master). Callee: cgreturn writes the slot through *(@sretarg) via the existing widener non-BP base (bare return stores the void tag); exact-type 'return f();' rides the #9 sret-forward. Receive: let/assign/discard reuse the generic #23/#10 sret protocol; the match scrutinee passes its spill slot as the sret dest (tagged-specific, no tuple precedent). This could NOT land as a gate-first interim loud-stop (the planned #38a): lib/errors/errors.ww errno() already returns a 40B (errors.error) slot in-tree — the cgenstmt.ww-documented #222 latent — so a bare gate breaks the build. errno graduates to sret here instead; errnotest pins it at runtime (its cstage run; the wwstage run was already failing at master via an unrelated pre-existing indirect-call arg-classification divergence, reported separately) and test/926's errno-shaped row reads the previously-dropped tail word on both stages. The unwired cursor consumers of an sret-class call result loud-stop (rule 7) rather than read a cursor the callee no longer fills: widening forward/receive ((A|B)->(A|B|C) mem-to-mem tag-remap, filed #40), ?/!/is/as operands, argument position, and the >48B tagged-arg class both stages previously mishandled silently. One-class-one-commit per the #133 carve-out: post-flip those consumers would read AX (now the dest pointer) as the tag — a gates-trailing commit would leave a silently-wrong bisect point, so the flip and its gates are not separable. test/926: 15 rows — 56B regex-shaped round-trips (literal/local/ assign/match-scrutinee/forward/str-variant/multi-call), 40B repro + bare-return-void, the errno-shaped tail-read graduation row, 32B boundary rows pinned register-ABI by asm sentinel, and 3 loud-stop rows pinned as build failures on both stages.