Reading a slice-typed tuple element (t.0) loaded only the pointer
word; len and cap took whatever was left in BX/CX — silent garbage in
BOTH stages once anything clobbered the registers between build and
read. Load all three header words at the tuple-element arm. Review
item #28.
Both stages move in one commit: one emission contract; splitting
would leave the byte-id gates red between the halves.
Hojun-Cho
0a6f500b8c