wcc/check: inferred-let tuple literal carries its slot-layout size — 0-size local smashed saved BP/RIP (#44)

The N_TUPLE expr arm built its TY_TUPLE with size 0 (only the
annotated N_TTUPLE resolve_type route computed the layout), and
type_default passes TY_TUPLE through, so an inferred
`let t = (4: size, 2: size)` planted a 0-size local at offset 0 —
the element stores landed on the saved BP/RIP and main segfaulted
on RET (cstage; the arg shape instead fell to the global-symbol
path and link-failed). wwstage (exprtype N_TUPLE -> tinfofornode)
was runtime-correct throughout — cstage aligns UP to it; all
fixed shapes are now byte-id. Slot rule mirrors the N_TTUPLE twin
and cgen tuple_eslot, with untyped elements sized at their
type_default (element types stay untyped for the consumer-side
assignability contract).

7 table rows in 941 pin the class (cast/bare/mixed/float elems,
destructure-from-local, call-arg, nested); each fails at master
e8977a4 cstage (segfault or link-fail + byte-id NO).

test/wcc/941_tuple_slot_layout_run.c

@@ -1849,6 +1849,82 @@ static const struct row rows[] = {
 	  "	return 0;\n"
 	  "};\n", 0,
 	  K_BUILDERR, "tagged cast source shape unwired" },
+
+	/* ---- task #44: INFERRED-let tuple literal — cstage's N_TUPLE
+	 * expr type carried size 0 (only the annotated N_TTUPLE route
+	 * computed the slot layout), so cgen's N_LET planted the local
+	 * at offset 0: the element stores landed on the saved BP/RIP
+	 * and main SEGFAULTED on RET. wwstage (exprtype N_TUPLE →
+	 * tinfofornode) was runtime-correct — the rare cstage-is-the-bug
+	 * polarity (#263 corollary). Every row below segfaulted (or, for
+	 * the arg row, link-failed on the off==0 global fallback) at
+	 * master e8977a4 cstage; all are byte-id post-fix. ---- */
+	{ "t44_inferred_let_cast",
+	  "package main;\n"
+	  "export fn main() i32 = {\n"
+	  "	let t = (4: size, 2: size);\n"
+	  "	if (t.0 != 4) { return 1; };\n"
+	  "	if (t.1 != 2) { return 2; };\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* bare untyped-int elements; the decl alone (no .N read) already
+	 * smashed the frame at master — the noread shape rides the same
+	 * row via the early stores. */
+	{ "t44_inferred_let_bare",
+	  "package main;\n"
+	  "export fn main() i32 = {\n"
+	  "	let t = (4, 2);\n"
+	  "	if (t.0 != 4) { return 1; };\n"
+	  "	if (t.1 != 2) { return 2; };\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	{ "t44_inferred_let_mixed3",
+	  "package main;\n"
+	  "export fn main() i32 = {\n"
+	  "	let t = (4: size, 2, 36: size);\n"
+	  "	if (t.0 + t.2 != 40) { return 1; };\n"
+	  "	if (t.1 != 2) { return 2; };\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	{ "t44_inferred_let_float",
+	  "package main;\n"
+	  "export fn main() i32 = {\n"
+	  "	let t = (1.5, 2.5);\n"
+	  "	if (t.0 + t.1 != 4.0) { return 1; };\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* destructure FROM the inferred local — the mlet source ident
+	 * resolved to the 0-size slot at offset 0 (same root). */
+	{ "t44_inferred_destructure",
+	  "package main;\n"
+	  "export fn main() i32 = {\n"
+	  "	let t = (40: size, 2: size);\n"
+	  "	let (a, b) = t;\n"
+	  "	if (a + b != 42) { return 1; };\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* inferred local as a tuple CALL ARG — at master the off==0 local
+	 * fell to the global-symbol path: `w6l: undefined reference to
+	 * 't'` (link-fail, not segfault — same root, different death). */
+	{ "t44_inferred_arg",
+	  "package main;\n"
+	  "fn add(t: (size, size)) size = {\n"
+	  "	return t.0 + t.1;\n"
+	  "};\n"
+	  "export fn main() i32 = {\n"
+	  "	let t = (40: size, 2: size);\n"
+	  "	if (add(t) != 42) { return 1; };\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* nested tuple element: slot rule gives an inner tuple one 8B
+	 * eightbyte (tuple_eslot parity) — pins the outer layout. */
+	{ "t44_inferred_nested",
+	  "package main;\n"
+	  "export fn main() i32 = {\n"
+	  "	let t = ((4, 2), 36);\n"
+	  "	if (t.1 != 36) { return 1; };\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
 };
 
 /* build+run via a driver (ww / ww_ww); returns 0 pass, nonzero fail. */