w6c+wwstage: aggregate let-init copy from a struct-DEF global (#268 reviewer)

The fold-1b unified arm (bb2f4e1) added an N_IDENT addressable-rhs source
setup, but the two stages gated the GLOBAL case differently: cstage used
let_islet || def_isarraydef, wwstage used isletvar || deflookup (ANY def).
On a struct-typed `def` used as an aggregate-copy rhs (`let c: T = G`)
wwstage copied the whole value (correct) while cstage truncated to the 8B
scalar tail — a cs!=ww divergence (rule-10). A struct-LET global already
copies on both, so the def gap was also an internal cstage inconsistency.

Struct defs are first-class laid-out aggregates (DATA storage + field
load, #129 A.2/A.3), so converge on the correct full copy on both: add
def_isstructdef to cstage's predicate and replace wwstage's broad
deflookup with the def_is{array,struct}def pairing already held identical
in defisaddressable. 949 +2 rows (array-def + struct-def global, full
readback, byteid=1).

test/wcc/949_dotbase_addr_slice_run.c

@@ -930,6 +930,30 @@ static const struct row rows[] = {
 	  "	return (c.m[0]+c.m[1]+c.m[2]+c.m[3]\n"
 	  "	      +c.m[4]+c.m[5]+c.m[6]+c.m[7]): i32;\n"
 	  "};\n", 36, 1 },
+	/* #268 reviewer: the addressable-rhs N_IDENT axis also covers a
+	 * laid-out-aggregate GLOBAL (#129 A.2/A.3) — an array `def` and a
+	 * struct `def`, both DATA-stored and LEAQ'd by symbol. The struct-
+	 * def case was the one cs!=ww divergence the unified arm shipped:
+	 * wwstage's deflookup (any def) copied it while cstage's def_is-
+	 * arraydef alone truncated, so they diverged (a struct-LET global
+	 * already copied on both, making the def gap an inconsistency).
+	 * Aligned both to copy via the def_is{array,struct}def pairing held
+	 * identical to defisaddressable. Full readback; byteid=1. */
+	{ "arraydef_global",
+	  "package main;\n"
+	  "def G: [4]u32 = [11u32, 22u32, 33u32, 44u32];\n"
+	  "export fn main() i32 = {\n"
+	  "	let c: [4]u32 = G;\n"
+	  "	return (c[0]+c[1]+c[2]+c[3]): i32;\n"
+	  "};\n", 110, 1 },
+	{ "structdef_global",
+	  "package main;\n"
+	  "type T = struct { a: u32, b: u32, c: u32, d: u32 };\n"
+	  "def G: T = T { a = 10u32, b = 20u32, c = 30u32, d = 40u32 };\n"
+	  "export fn main() i32 = {\n"
+	  "	let c: T = G;\n"
+	  "	return (c.a+c.b+c.c+c.d): i32;\n"
+	  "};\n", 100, 1 },
 	{ NULL, NULL, 0, 0 }
 };