wcc+w6c+w6c_ww: global tuple lets — DATA emit + element reads + len(g.N) (C-t3, #48)

Global tuple lets were WHOLLY unwired, silently: let_emit_size returned
0 so emit_lets SKIPPED the definition (no DATA, no diagnostic), then
cstage's t.N read and #235 len arm read BP-frame garbage (localfind→0)
while wwstage — with the tuple never in collectlets — mis-emitted the
field index as a symbol (`MOVQ 0(SB), AX`). ken's #48 was the len()
facet of this.

Now: let_emit_size/letemitsize admit TY_TUPLE (slot-sum size, rides
C-t0); emit_tuple_data/emittupledata lay the slot-format DATAW row —
a scalar element one 8B LE word, a str element its 24B header slot
with a DATAR ptr patch at the element's slot offset (the #18 [N]str
per-element pattern; strlits pre-interned in element order) — and any
element that doesn't reduce to an int/str literal dies LOUD instead
of skipped. The t.N read and len arms gain the global base (LEAQ
sym(SB) into CX, the struct-field-global pattern; wwstage's C5 len
loud-stop graduates to the working path). A GLOBAL tuple as a
first-class VALUE (`let q = g;`) loud-stops on both stages — pre-fix
it byte-identically loaded word0 only and read a stale cursor for
words 1+ (element reads are the supported surface).

941 grows the t3 rows: global element reads (str+i64 and packed
u32,u32 incl. len(g.0)) + rejects (float-element init, whole-value
use, pre-existing element-write anchor). 7/82 checks fail at the
C-t2 parent (cs silent-garbage runtime, ww C5 build-fail, both
rejects vacuous-or-absent).

test/wcc/941_tuple_slot_layout_run.c

@@ -436,6 +436,52 @@ static const struct row rows[] = {
 	  "	return 0;\n"
 	  "};\n", 0,
 	  K_BUILDERR, "element kind unsupported" },
+
+	/* ---- C-t3 (#48): GLOBAL tuples. Pre-C-t3 the definition was
+	 * SILENTLY skipped (let_emit_size 0 → no DATA, no diagnostic);
+	 * cstage element reads then read BP-frame garbage (localfind→0)
+	 * and wwstage mis-emitted the field index as a symbol
+	 * (`MOVQ 0(SB), AX`). Now: slot-laid DATAW (+ DATAR str-element
+	 * ptr patches), element reads + len(g.N) via LEAQ sym(SB);
+	 * unsupported element inits and the whole-tuple-as-value shape
+	 * die LOUD. ---- */
+	{ "t3_global_elem",
+	  "package main;\n"
+	  "let g: (str, i64) = (\"hello\", 9);\n"
+	  "let h: (u32, u32) = (5, 6);\n"
+	  "export fn main() i32 = {\n"
+	  "	if (len(g.0) != 5) { return 1; };\n"
+	  "	if (g.1 != 9) { return 2; };\n"
+	  "	if (h.0 != 5) { return 3; };\n"
+	  "	if (h.1 != 6) { return 4; };\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	{ "t3_reject_float_global",
+	  "package main;\n"
+	  "let g: (f64, i64) = (2.5, 4);\n"
+	  "export fn main() i32 = {\n"
+	  "	if (g.1 != 4) { return 1; };\n"
+	  "	return 0;\n"
+	  "};\n", 0,
+	  K_BUILDERR, "unsupported element init (int/str literals only; rule 7)" },
+	{ "t3_reject_whole_value",
+	  "package main;\n"
+	  "let g: (i64, i64) = (3, 4);\n"
+	  "export fn main() i32 = {\n"
+	  "	let q: (i64, i64) = g;\n"
+	  "	if (q.0 != 3) { return 1; };\n"
+	  "	return 0;\n"
+	  "};\n", 0,
+	  K_BUILDERR, "global tuple as a first-class value unwired" },
+	/* pre-existing loud (no-regress pin): global tuple element WRITE. */
+	{ "t3_reject_global_write",
+	  "package main;\n"
+	  "let g: (i64, i64) = (3, 4);\n"
+	  "export fn main() i32 = {\n"
+	  "	g.0 = 7;\n"
+	  "	return 0;\n"
+	  "};\n", 0,
+	  K_BUILDERR, "unsupported assign target shape" },
 };
 
 /* build+run via a driver (ww / ww_ww); returns 0 pass, nonzero fail. */