cgen: load the full header for a wwstage global-dot slice field

let x: []T = g.buf on a module-global struct dispatched only str
fields to the 3-word header load; a []T field fell to the scalar
tail (ptr word only), so len/cap read stale registers and the shape
was byteid-divergent against cstage's TY_STR||TY_SLICE arm (#263).

internal/wwfixture/types.ww

@@ -1,13 +1,13 @@
 package wwfixture;
 
 def protocolversion: i32 = 1;
-def corpuscount: i32 = 1229;
+def corpuscount: i32 = 1230;
 def errorcount: i32 = 314;
 def compilecount: i32 = 12;
-def runcount: i32 = 137;
+def runcount: i32 = 138;
 def runexitcount: i32 = 766;
-def nativecount: i32 = 2458;
+def nativecount: i32 = 2460;
-def corpushash: str = "9d1db4b4bdde1b7e2b1f2e2ae5ca6c6b91b0162df585fd877021d27ec6863d89";
+def corpushash: str = "fd04059b05a19ae63f1bec3edaefedf1d8ce9a505302a153434457d0fb9b9eca";
 
 type directive = enum i32 {
 	ERROR = 0,

selfhost/cmd/wcc/cgenexpr.ww

@@ -4242,7 +4242,12 @@ fn cgdot(c: *cgen, n: *syntax.node) void = {
 							cgloadtaggedfield(c, "CX", foff, tsz, true);
 							return;
 						};
-						if (syntax.typeisstr(ftraw)) {
+						// slice joins the str header load (#263: cstage
+						// N_DOT chain arm keys TY_STR||TY_SLICE — the
+						// same 24B {ptr,len,cap}); the scalar tail below
+						// pulled ONLY .ptr, so len(g.buf) read garbage.
+						if (syntax.typeisstr(ftraw)
+						    || syntax.typeisslice(ftraw)) {
 							emitline("\tMOVQ\t");
 							emitdispreg(foff: i64, "CX");
 							emitline(", AX\n");

test/wcc/data/globaldot_slicefield_hdr/case.ww

@@ -0,0 +1,25 @@
+//ww:run
+// A module-global struct's slice field read BY VALUE must load the
+// full 24B {ptr,len,cap} header. The pre-fix wwstage global-dot arm
+// dispatched only str fields to the header load; a []T field fell to
+// the scalar tail (ptr word only) and len(x) read stale registers.
+package main;
+
+type box = struct {
+	buf: []i32,
+	name: str,
+};
+
+let g: box = box{};
+
+export fn main() int = {
+	let arr: [4]i32 = [10, 20, 30, 40];
+	g.buf = arr[:];
+	g.name = "globals";
+	let x: []i32 = g.buf;
+	if (len(x) != 4) { return 1; };
+	if (x[2] != 30) { return 2; };
+	let s: str = g.name;
+	if (len(s) != 7) { return 3; };
+	return 0;
+};