Make web document navigation survive live-updating pages

Recreated-node caret recovery, tolerant caret validation, per-root retained document trees and cursors across tab switches, document warm-up, coalesced structural moves, and hung-provider fast-fail with an 'Application is not responding' announcement.

internal/atspi/document_view_test.go

@@ -110,6 +110,43 @@ func TestNavigationDocumentValidatesOnlyTraversedBranches(t *testing.T) {
 	}
 }
 
+// Caret moves read text and line bounds live from the provider, so text,
+// geometry, or child-order staleness along the traversed range must not
+// force a recapture first: on ticking pages some counter between caret and
+// target is always mid-update, and strict validation traps the caret no
+// matter how often it recaptures. Identity and semantics stay strict, and
+// the strict range validation used by structural navigation is unchanged.
+func TestValidateDocumentCaretRangeToleratesTextAndGeometryStaleness(t *testing.T) {
+	for _, test := range []struct {
+		name       string
+		invalidate func(*AccessibleTree)
+		want       error
+		wantStrict error
+	}{
+		{"text", func(tree *AccessibleTree) { tree.InvalidateText(testID("/link")) }, nil, ErrStaleText},
+		{"geometry", func(tree *AccessibleTree) { tree.InvalidateGeometry(testID("/inner")) }, nil, ErrStaleGeometry},
+		{"semantics", func(tree *AccessibleTree) { tree.InvalidateSnapshot(testID("/link")) }, ErrStaleSnapshot, ErrStaleSnapshot},
+		{"children", func(tree *AccessibleTree) { tree.MarkChildrenChanged(testID("/inner")) }, nil, ErrIncompleteTree},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			tree, _ := NewAccessibleTree(testID("/root"), documentTestNodes())
+			ref, _ := tree.Reference(testID("/heading"))
+			view, err := tree.NavigationDocument(context.Background(), ref)
+			if err != nil {
+				t.Fatal(err)
+			}
+			test.invalidate(tree)
+			heading, _ := view.Index(ref.ID())
+			if err := tree.ValidateDocumentCaretRange(context.Background(), view, heading, len(view.Nodes)-1); !errors.Is(err, test.want) {
+				t.Fatalf("caret validation: %v, want %v", err, test.want)
+			}
+			if err := tree.ValidateDocumentRange(context.Background(), view, heading, len(view.Nodes)-1); !errors.Is(err, test.wantStrict) {
+				t.Fatalf("strict validation changed: %v, want %v", err, test.wantStrict)
+			}
+		})
+	}
+}
+
 func TestNavigationDocumentRejectsRetiredViewsAndCanceledMoves(t *testing.T) {
 	tree, _ := NewAccessibleTree(testID("/root"), documentTestNodes())
 	ref, _ := tree.Reference(testID("/heading"))