Hojun-Cho
153c7b3b46
A multi-float tuple return mis-routed: SEND pushed a stale AX leaving the float stranded in X0, while RECV (#105) read every float from X0 — so a (f64,f64) return collided both floats. Add an SSE cursor [X0,X1] parallel to the GP cursor [AX,DX,CX,R8], placing each element by its SysV class + within-class index (ref/qbe/amd64/sysv.c retr), symmetric send/recv across both stages, via a generic tuple_store/tupstore+tupsse helper that #171 will reuse for struct-return convergence. (f64,f64,f64) = 3 SSE eightbytes exceeds the 2-register cap and now fails loud (rule 7) rather than colliding. Unifying the 16B and 32B whole-tuple-single-var branches onto the dual cursor was required for f64+str coexistence; it also fixes a latent str-first single-var bug (the old 32B branch read .ptr from DX while the send placed it in AX). No str-first or 32B tuple exists in-tree, so integer paths stay byte-identical (990-997 green).