test/949: slice-of-non-array-field call-arg guard rows (#257)

The #257 call-arg fix routes the N_SLICE base through the array-gated
cg_dotbase_addr/dotbaseaddr helper. Add the load-bearing deviation
guard: a slice of a []T field and of a str field passed straight as a
call arg must FALL THROUGH the gate to cgexpr (header .ptr load), not
take the field address. Both also exercise the N_DOT esz extension on
the fall-through arm (re-slice by element width). cs==ww byte-id.

test/wcc/949_dotbase_addr_slice_run.c

@@ -451,6 +451,35 @@ static const struct row rows[] = {
 	  "	a[1] = 66u8;\n"
 	  "	return rd(a[1:4]);\n"
 	  "};\n", 66, 1 },
+	/* Helper-deviation guard rows (load-bearing): a slice of a NON-array
+	 * field (`[]T` field, str field) passed as a call arg must FALL
+	 * THROUGH the array-gated cg_dotbase_addr/dotbaseaddr to cgexpr,
+	 * which loads the field's slice/str HEADER .ptr — NOT take the field
+	 * ADDRESS (that would treat the header words as inline array data).
+	 * The N_DOT esz extension also applies on the fall-through arm: the
+	 * slice is re-sliced by the element width (esz=4 for []i32), so
+	 * q.v[1:3][0] = backing[1]. If the gate over-fired (emitted &field),
+	 * .ptr would point at the header itself -> wrong value / segfault. */
+	{ "callarg_slicefield",
+	  "package main;\n"
+	  "type w = struct { v: []i32 };\n"
+	  "fn rd(s: []i32) i32 = { return s[0]; };\n"
+	  "export fn main() i32 = {\n"
+	  "	let backing: [4]i32;\n"
+	  "	backing[1] = 88;\n"
+	  "	let q: w;\n"
+	  "	q.v = backing[0:4];\n"
+	  "	return rd(q.v[1:3]);\n"
+	  "};\n", 88, 1 },
+	{ "callarg_strfield",
+	  "package main;\n"
+	  "type w = struct { v: str };\n"
+	  "fn rd(s: str) i32 = { return len(s): i32; };\n"
+	  "export fn main() i32 = {\n"
+	  "	let q: w;\n"
+	  "	q.v = \"hello\";\n"
+	  "	return rd(q.v[1:4]);\n"
+	  "};\n", 3, 1 },
 	{ NULL, NULL, 0, 0 }
 };