fix(page-visibility): keep synthetic iframe documents hidden

Reading contentWindow on an iframe in a windowless document must not make
its synthetic child document visible. Determine browsing-context ownership
from native top-level, child frame, and popup registrations, preserving
the document's retained visibility state separately from defaultView.

Cover both getter access orders, nested synthetic frames, and cross-realm
visibility/defaultView getters on live documents and popups.

Follow-up to #501.

moli-renderer-v8/src/native_bridge/document.rs

@@ -1450,18 +1450,25 @@ fn current_script_belongs_to_document(
         .is_some_and(|owner_document| owner_document == document_handle)
 }
 
-fn document_is_hidden<'s>(
-    scope: &mut v8::PinScope<'s, '_>,
-    runtime_ptr: *mut JsContextHost,
-    handle: DomHandle,
-    document: v8::Local<'s, v8::Object>,
-) -> bool {
-    unsafe { &*runtime_ptr }
+fn document_has_browsing_context(runtime: &JsContextHost, handle: DomHandle) -> bool {
+    // Detached iframe compatibility windows can become a document's defaultView
+    // without registering a browsing context. They must not make it visible.
+    runtime.dom_host().document_handle() == handle
+        || runtime
+            .child_browsing_context_host_for_document_handle(handle)
+            .is_some()
+        || runtime
+            .lightweight_popup_id_for_document_handle(handle)
+            .is_some()
+}
+
+fn document_is_hidden(runtime: &JsContextHost, handle: DomHandle) -> bool {
+    runtime
         .dom_host()
         .node(handle)
         .and_then(Node::as_document)
-        .is_some_and(|document| document.visibility_hidden())
-        || document_associated_window_for_object(scope, runtime_ptr, handle, document).is_none()
+        .is_none_or(|document| document.visibility_hidden())
+        || !document_has_browsing_context(runtime, handle)
 }
 
 fn document_hidden_getter_function<'s>(
@@ -1474,7 +1481,7 @@ fn document_hidden_getter_function<'s>(
         rv.set_undefined();
         return;
     };
-    rv.set_bool(document_is_hidden(scope, runtime_ptr, handle, args.this()));
+    rv.set_bool(document_is_hidden(unsafe { &*runtime_ptr }, handle));
 }
 
 fn document_visibility_state_getter_function<'s>(
@@ -1487,7 +1494,7 @@ fn document_visibility_state_getter_function<'s>(
         rv.set_undefined();
         return;
     };
-    let state = if document_is_hidden(scope, runtime_ptr, handle, args.this()) {
+    let state = if document_is_hidden(unsafe { &*runtime_ptr }, handle) {
         "hidden"
     } else {
         "visible"

moli-renderer-v8/src/script_vm/tests/dom_elements/detached.rs

@@ -3474,6 +3474,58 @@ fn detached_document_view_uses_document_prototype_accessors() {
     );
 }
 
+#[test]
+fn detached_iframe_windows_do_not_change_document_visibility() {
+    let mut vm = new_storage_test_vm("https://detached-iframe-visibility.test/");
+
+    let result = vm
+        .eval(
+            r#"
+(() => {
+  const errors = [];
+  const check = (condition, message) => { if (!condition) errors.push(message); };
+  const factories = [
+    ["createHTMLDocument", () => document.implementation.createHTMLDocument("")],
+    ["DOMParser", () => new DOMParser().parseFromString("<body></body>", "text/html")],
+    ["createDocument", () => document.implementation.createDocument("urn:test", "root", null)]
+  ];
+  for (const [name, create] of factories) {
+    for (const first of ["document", "window"]) {
+      const outer = create();
+      const frame = outer.createElementNS("http://www.w3.org/1999/xhtml", "iframe");
+      frame.srcdoc = "<p>hello</p>";
+      outer.documentElement.appendChild(frame);
+      const label = `${name}/${first}`;
+      check(outer.defaultView === null, `${label}: windowless owner`);
+      let child;
+      if (first === "document") {
+        child = frame.contentDocument;
+        check(child.hidden && child.visibilityState === "hidden", `${label}: before contentWindow`);
+      }
+      const view = frame.contentWindow;
+      child ||= frame.contentDocument;
+      check(view !== null && view.document === child, `${label}: synthetic window`);
+      check(child.defaultView === view, `${label}: associated window retained`);
+      check(child.hidden && child.visibilityState === "hidden", `${label}: after contentWindow`);
+      check(outer.hidden && outer.visibilityState === "hidden", `${label}: owner stays hidden`);
+      const nested = child.createElement("iframe");
+      nested.srcdoc = "<p>nested</p>";
+      child.body.appendChild(nested);
+      const nestedChild = nested.contentDocument;
+      check(nestedChild.hidden && nestedChild.visibilityState === "hidden", `${label}: nested before contentWindow`);
+      check(nested.contentWindow.document === nestedChild, `${label}: nested window`);
+      check(nestedChild.hidden && nestedChild.visibilityState === "hidden", `${label}: nested after contentWindow`);
+    }
+  }
+  return JSON.stringify(errors);
+})()
+"#,
+        )
+        .expect("detached iframe visibility probe should evaluate");
+
+    assert_eq!(result, "[]");
+}
+
 #[test]
 fn detached_document_state_and_collections_use_document_prototype_accessors() {
     let mut vm = new_storage_test_vm("https://detached-document-prototype-state.test/");

moli-renderer-v8/src/script_vm/tests/dom_elements/live_document.rs

@@ -52,6 +52,65 @@ fn input_show_picker_enforces_brand_without_rejecting_inherited_child_origin() {
     );
 }
 
+#[test]
+fn document_visibility_and_default_view_follow_receiver_across_realms() {
+    let mut vm = new_storage_test_vm("https://document-visibility-realms.test/");
+
+    vm.eval(
+        r#"
+(() => {
+  const frame = document.createElement("iframe");
+  frame.id = "visibility-live-frame";
+  (document.body || document.documentElement || document).appendChild(frame);
+})()
+"#,
+    )
+    .expect("visibility child frame should be created");
+    materialize_single_child_default_realm_for_test(
+        &mut vm,
+        "document visibility and defaultView child Realm",
+    );
+
+    let result = vm
+        .eval(
+            r#"
+(() => {
+  const errors = [];
+  const check = (condition, message) => { if (!condition) errors.push(message); };
+  const childWindow = document.getElementById("visibility-live-frame").contentWindow;
+  const child = childWindow.document;
+  const parentView = Object.getOwnPropertyDescriptor(Document.prototype, "defaultView").get;
+  const childView = Object.getOwnPropertyDescriptor(childWindow.Document.prototype, "defaultView").get;
+  const parentHidden = Object.getOwnPropertyDescriptor(Document.prototype, "hidden").get;
+  const childHidden = Object.getOwnPropertyDescriptor(childWindow.Document.prototype, "hidden").get;
+  const parentVisibility = Object.getOwnPropertyDescriptor(Document.prototype, "visibilityState").get;
+  const childVisibility = Object.getOwnPropertyDescriptor(childWindow.Document.prototype, "visibilityState").get;
+  check(parentView.call(document) === window, "parent defaultView");
+  check(parentView.call(child) === childWindow, "parent getter on child defaultView");
+  check(childView.call(document) === window, "child getter on parent defaultView");
+  check(childView.call(child) === childWindow, "child defaultView");
+  check(!parentHidden.call(child) && parentVisibility.call(child) === "visible", "child is visible through parent getters");
+  check(!childHidden.call(document) && childVisibility.call(document) === "visible", "parent is visible through child getters");
+  const windowless = child.implementation.createHTMLDocument("");
+  check(childView.call(windowless) === null, "windowless defaultView through child getter");
+  check(parentHidden.call(windowless) && parentVisibility.call(windowless) === "hidden", "windowless remains hidden through parent getters");
+  const popup = window.open("about:blank", "visibility-popup");
+  check(popup !== null, "popup created");
+  try {
+    check(!popup.document.hidden && popup.document.visibilityState === "visible", "live popup is visible");
+    check(parentView.call(popup.document) === popup, "popup defaultView through parent getter");
+  } finally {
+    popup.close();
+  }
+  return JSON.stringify(errors);
+})()
+"#,
+        )
+        .expect("cross-realm document visibility and view probe should evaluate");
+
+    assert_eq!(result, "[]");
+}
+
 #[test]
 fn cross_realm_dom_bindings_reject_incompatible_receivers_in_their_own_realm() {
     let mut vm = new_storage_test_vm("https://cross-realm-dom-receivers.test/");