fix(display/webkit): WindowExists unwraps the query's typed nil

go/display/webkit/window_helpers.go

@@ -185,5 +185,13 @@ func WindowExists(c *core.Core, name string) bool {
 		return false
 	}
 	r := c.QUERY(window.QueryWindowByName{Name: name})
-	return r.OK && r.Value != nil
+	if !r.OK {
+		return false
+	}
+	// The query answers a miss with a typed-nil *WindowInfo inside the
+	// Result, and a typed nil still passes an interface nil-check — so
+	// trusting r.Value != nil made every name exist, and callers took
+	// warm-window paths against windows that were never created.
+	info, ok := r.Value.(*window.WindowInfo)
+	return ok && info != nil
 }

go/display/webkit/window_helpers_behaviour_test.go

@@ -82,3 +82,19 @@ func TestWindowHelpersBehaviour_WindowExists_Bad(t *core.T) {
 	core.AssertFalse(t, WindowExists(c, "chat"))
 	core.AssertFalse(t, HideWindow(c, "chat"))
 }
+
+// A window service that answers the query but misses returns a TYPED nil
+// *WindowInfo inside the Result — which an interface nil-check passes.
+// WindowExists must unwrap the value, or every name "exists" and callers
+// take warm-window paths against windows that were never created.
+func TestWindowHelpersBehaviour_WindowExists_Ugly(t *core.T) {
+	c := core.New(core.WithServiceLock())
+	c.RegisterQuery(func(_ *core.Core, q core.Query) core.Result {
+		if _, ok := q.(window.QueryWindowByName); ok {
+			return core.Result{Value: (*window.WindowInfo)(nil), OK: true}
+		}
+		return core.Result{}
+	})
+
+	core.AssertFalse(t, WindowExists(c, "never-created"))
+}