w6c+wwstage: array return-by-value via the struct-return ABI (#267 fold-2)

Wire TY_ARRAY into the existing struct-return gates so arrays ride the
same reg-class (<=24B in AX:DX:CX) / sret-class (>24B) path the struct
return ABI already emits byte-identically. No new ABI machinery.

Both stages, uniform gate-widen:
- cg_sret_retsize / sretretsize: +TY_ARRAY (natural size sub.size*len,
  the type table) -> auto-enables sret send/recv + the >24B sret N_IDENT
  word-copy + return-forward, all keyed on the shared sret SSoT.
- cgreturn <=24B reg-send: +TY_ARRAY (N_IDENT scratch word-copy ->
  AX/DX/CX). reg-class return-forward rides the default cgexpr passthrough.
- let-init / assign <=24B recv: +TY_ARRAY (AX/DX/CX sized stores).

struct_float_class stays struct-only: pure-int element arrays only; no
pure-float-array-return consumer exists today.

949 +11 rows: reg-class 8/16/24B + sret-class 32B, [N]u32 and [N]u8,
at let-init/assign/return-forward, full-member readback, + a struct-
return regression control. All cstage-run + cs==ww byte-id.

test/wcc/949_dotbase_addr_slice_run.c

@@ -954,6 +954,72 @@ static const struct row rows[] = {
 	  "	let c: T = G;\n"
 	  "	return (c.a+c.b+c.c+c.d): i32;\n"
 	  "};\n", 100, 1 },
+	/* #267 fold-2: array return-by-value ABI. Arrays ride the existing
+	 * struct-return path (≤24B in AX:DX:CX, >24B via sret) — these rows
+	 * pin the runtime value AND cs==ww byte-id across reg-class (8/16/
+	 * 24B) and sret-class (32B), [N]u32 and [N]u8, at the let-init /
+	 * assign / return-forward receive contexts. ctrl_struct_ret is the
+	 * regression control: a struct return still byte-id (the struct path
+	 * the arrays were wired into didn't change). FULL readback (sum every
+	 * member) so a dropped eightbyte surfaces. */
+	{ "ret_arr_u32_8",
+	  "package main;\n"
+	  "fn mk() [2]u32 = { let a: [2]u32; a[0]=3u32; a[1]=4u32; return a; };\n"
+	  "export fn main() i32 = { let c = mk(); return (c[0]+c[1]): i32; };\n",
+	  7, 1 },
+	{ "ret_arr_u32_16",
+	  "package main;\n"
+	  "fn mk() [4]u32 = { let a: [4]u32; a[0]=1u32;a[1]=2u32;a[2]=3u32;a[3]=4u32; return a; };\n"
+	  "export fn main() i32 = { let c = mk(); return (c[0]+c[1]+c[2]+c[3]): i32; };\n",
+	  10, 1 },
+	{ "ret_arr_u32_24",
+	  "package main;\n"
+	  "fn mk() [6]u32 = { let a: [6]u32; a[0]=1u32;a[1]=2u32;a[2]=3u32;a[3]=4u32;a[4]=5u32;a[5]=6u32; return a; };\n"
+	  "export fn main() i32 = { let c = mk(); return (c[0]+c[1]+c[2]+c[3]+c[4]+c[5]): i32; };\n",
+	  21, 1 },
+	{ "ret_arr_u32_32_sret",
+	  "package main;\n"
+	  "fn mk() [8]u32 = { let a: [8]u32; a[0]=1u32;a[1]=2u32;a[2]=3u32;a[3]=4u32;a[4]=5u32;a[5]=6u32;a[6]=7u32;a[7]=8u32; return a; };\n"
+	  "export fn main() i32 = { let c = mk(); return (c[0]+c[1]+c[2]+c[3]+c[4]+c[5]+c[6]+c[7]): i32; };\n",
+	  36, 1 },
+	{ "ret_arr_u8_4",
+	  "package main;\n"
+	  "fn mk() [4]u8 = { let a: [4]u8; a[0]=10u8;a[1]=20u8;a[2]=30u8;a[3]=40u8; return a; };\n"
+	  "export fn main() i32 = { let c = mk(); return (c[0]+c[1]+c[2]+c[3]): i32; };\n",
+	  100, 1 },
+	{ "ret_arr_u8_32_sret",
+	  "package main;\n"
+	  "fn mk() [32]u8 = { let a: [32]u8; a[0]=50u8;a[15]=30u8;a[31]=40u8; return a; };\n"
+	  "export fn main() i32 = { let c = mk(); return (c[0]+c[15]+c[31]): i32; };\n",
+	  120, 1 },
+	{ "ret_arr_assign_16",
+	  "package main;\n"
+	  "fn mk() [4]u32 = { let a: [4]u32; a[0]=1u32;a[1]=2u32;a[2]=3u32;a[3]=4u32; return a; };\n"
+	  "export fn main() i32 = { let c: [4]u32; c = mk(); return (c[0]+c[1]+c[2]+c[3]): i32; };\n",
+	  10, 1 },
+	{ "ret_arr_assign_32_sret",
+	  "package main;\n"
+	  "fn mk() [8]u32 = { let a: [8]u32; a[0]=1u32;a[7]=8u32; return a; };\n"
+	  "export fn main() i32 = { let c: [8]u32; c = mk(); return (c[0]+c[7]): i32; };\n",
+	  9, 1 },
+	{ "ret_arr_fwd_16",
+	  "package main;\n"
+	  "fn mk() [4]u32 = { let a: [4]u32; a[0]=1u32;a[1]=2u32;a[2]=3u32;a[3]=4u32; return a; };\n"
+	  "fn fwd() [4]u32 = { return mk(); };\n"
+	  "export fn main() i32 = { let c = fwd(); return (c[0]+c[1]+c[2]+c[3]): i32; };\n",
+	  10, 1 },
+	{ "ret_arr_fwd_32_sret",
+	  "package main;\n"
+	  "fn mk() [8]u32 = { let a: [8]u32; a[0]=1u32;a[7]=8u32; return a; };\n"
+	  "fn fwd() [8]u32 = { return mk(); };\n"
+	  "export fn main() i32 = { let c = fwd(); return (c[0]+c[7]): i32; };\n",
+	  9, 1 },
+	{ "ctrl_struct_ret",
+	  "package main;\n"
+	  "type T = struct { a: u32, b: u32, c: u32 };\n"
+	  "fn mk() T = { let s: T; s.a=1u32;s.b=2u32;s.c=3u32; return s; };\n"
+	  "export fn main() i32 = { let v = mk(); return (v.a+v.b+v.c): i32; };\n",
+	  6, 1 },
 	{ NULL, NULL, 0, 0 }
 };