test(verifier): cover keyboardRegionTop, including the decor-view guard

The full-screen IME decor view rejection had no test; removing it left the
suite green. Add direct cases: no keyboard -> sentinel, decor view ignored in
favor of the real keyboard line, and decor-only -> sentinel.

internal/verifier/worker_test.go

@@ -1,6 +1,7 @@
 package verifier
 
 import (
+	"math"
 	"testing"
 
 	"github.com/priyanshujain/sanderling/internal/hierarchy"
@@ -21,3 +22,44 @@ func TestVerbAcceptsSwipeRequiresPositiveBounds(t *testing.T) {
 		t.Error("swipes must accept an element with positive bounds")
 	}
 }
+
+// TestKeyboardRegionTop covers the region detection that keeps the fuzzer off
+// keyboard keys, especially the guard that ignores the IME's full-screen decor
+// view (which otherwise reports a huge bounds and would push the keyboard line
+// to the top of the screen, excluding the whole app).
+func TestKeyboardRegionTop(t *testing.T) {
+	ime := func(top, bottom int) *hierarchy.Element {
+		return &hierarchy.Element{
+			ResourceID: "com.google.android.inputmethod.latin:id/keyboard_holder",
+			Bounds:     hierarchy.Bounds{Right: 1080, Top: top, Bottom: bottom},
+		}
+	}
+	app := func(top, bottom int) *hierarchy.Element {
+		return &hierarchy.Element{ResourceID: "app/field", Bounds: hierarchy.Bounds{Right: 1080, Top: top, Bottom: bottom}}
+	}
+
+	t.Run("no keyboard yields sentinel", func(t *testing.T) {
+		tree := &hierarchy.Tree{Elements: []*hierarchy.Element{app(0, 2400)}}
+		if got := keyboardRegionTop(tree); got != math.MaxInt {
+			t.Errorf("keyboardRegionTop = %d, want MaxInt with no keyboard", got)
+		}
+	})
+
+	t.Run("decor view ignored, real keyboard sets the line", func(t *testing.T) {
+		tree := &hierarchy.Tree{Elements: []*hierarchy.Element{
+			app(0, 2400),
+			ime(0, 2400),    // full-screen IME decor view: must be ignored
+			ime(1503, 2268), // the actual keyboard
+		}}
+		if got := keyboardRegionTop(tree); got != 1503 {
+			t.Errorf("keyboardRegionTop = %d, want 1503 (keyboard top, not the decor view's 0)", got)
+		}
+	})
+
+	t.Run("decor-only view yields sentinel", func(t *testing.T) {
+		tree := &hierarchy.Tree{Elements: []*hierarchy.Element{app(0, 2400), ime(0, 2400)}}
+		if got := keyboardRegionTop(tree); got != math.MaxInt {
+			t.Errorf("keyboardRegionTop = %d, want MaxInt when only a full-screen IME decor view is present", got)
+		}
+	})
+}