wwstage struct-return RECV and RETURN used unrounded / round-to-8 sizes where
cstage uses the maxalign-rounded lu->size / rt->size, so a struct with maxalign
8 and a sub-8 tail (e.g. struct{i64,i32}) — or a maxalign<8 struct on the
return path — unpacked with a different trailing-word width (MOVL vs MOVQ)
between stages. Value-correct either way, but a cs!=ww asm divergence.
Add a dedicated structabisize = round(natural, maxalign) used only at the two
register-ABI sites. structnaturalsize stays unrounded: cstage's >24B sret and
memory-move path (cgen.c:8150, Task #33) genuinely uses the unrounded natural
size, so the two are different sizes — rounding the shared metric breaks 995.
maxalign derives from each field's tinfo.align (mirrors cstage check.c:708),
not an fsz ladder (a ladder over-rounds composite [N]u8 fields).
Gate-blind (no bootstrap struct hits the maxalign-8+tail shape) — the
discriminator is the cs==ww .s byte-cmp; covered by probe 698.
Hojun-Cho
d4e500f61c