fix(dom): getRootNode honours the composed option (−1)

`getRootNode()` ignored its options and always walked to the topmost node,
crossing shadow boundaries (a ShadowRoot's `_parent` is its host). Per DOM "get
the root", the default (`composed: false`) returns the node's own root and stops
at a shadow boundary; only `composed: true` returns the shadow-including root.
So a node in a shadow tree now returns its ShadowRoot, not the document.

The one internal consumer relying on the old shadow-crossing behaviour —
`moveBefore`'s same-(shadow-including-)tree check — now passes `{composed: true}`
explicitly (the symmetric WPT allowlist caught this regression on regen).

Clears rootNode.html. Gate 660/0/15, gem 1586/0/35, 0 regressions (incl.
moveBefore). Shadow-only public-API semantics, not a hot path.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ursm

lib/capybara/simulated/js/bridge.bundle.js

@@ -7071,9 +7071,13 @@
       this.nodeType = NODE_ELEMENT;
       this._ownerDoc = null;
     }
-    getRootNode(_options) {
+    getRootNode(options) {
+      const composed = !!(options && options.composed);
       let cur = this;
-      while (cur._parent) cur = cur._parent;
+      while (cur._parent) {
+        if (!composed && cur._isShadowRoot) break;
+        cur = cur._parent;
+      }
       return cur;
     }
     // Per DOM, `nodeValue` is null for every node type except Attr (its value)
@@ -12528,7 +12532,7 @@
     assertNodeArg(node);
     if (child != null) assertNodeArg(child);
     const parent = this;
-    if (node.getRootNode() !== parent.getRootNode()) {
+    if (node.getRootNode({ composed: true }) !== parent.getRootNode({ composed: true })) {
       throw hierarchyError("moveBefore: node and new parent are not in the same tree");
     }
     if (isInclusiveAncestor(node, parent)) {

lib/capybara/simulated/js/src/dom-nodes.js

@@ -758,9 +758,18 @@ class Node {
     this._ownerDoc  = null;    // set by createElement/adopt; pre-init keeps the hidden class STABLE so the
                                // per-element hot readers (find/visible_text/cascade) hit monomorphic ICs.
   }
-  getRootNode(_options) {
+  getRootNode(options) {
+    // DOM "get the root": the topmost node reached by following `_parent`.
+    // `composed: false` (the default) stops at a shadow boundary — a
+    // ShadowRoot's `_parent` IS its host, so without the break we'd cross into
+    // the light tree and wrongly report the document. `composed: true` returns
+    // the shadow-INCLUDING root and keeps climbing across the boundary.
+    const composed = !!(options && options.composed);
     let cur = this;
-    while (cur._parent) cur = cur._parent;
+    while (cur._parent) {
+      if (!composed && cur._isShadowRoot) break;
+      cur = cur._parent;
+    }
     return cur;
   }
   // Per DOM, `nodeValue` is null for every node type except Attr (its value)
@@ -5853,10 +5862,11 @@ function moveBeforeImpl(node, child) {
 
   const parent = this;
   // Ensure pre-move validity (https://whatpr.org/dom/1307.html#concept-node-ensure-pre-move-validity).
-  // 1. node and parent must share a shadow-including root (getRootNode already
-  //    crosses shadow boundaries via ShadowRoot._parent = host). This subsumes
-  //    the "both connected", cross-document and cross-tree cases.
-  if (node.getRootNode() !== parent.getRootNode()) {
+  // 1. node and parent must share a shadow-including root. `composed: true`
+  //    crosses shadow boundaries (ShadowRoot._parent = host) — plain
+  //    getRootNode() now stops at a shadow root per spec. This subsumes the
+  //    "both connected", cross-document and cross-tree cases.
+  if (node.getRootNode({ composed: true }) !== parent.getRootNode({ composed: true })) {
     throw hierarchyError('moveBefore: node and new parent are not in the same tree');
   }
   // 2. node must not be a (host-including) inclusive ancestor of parent.

spec/support/wpt_expected_failures.yml

@@ -337,9 +337,6 @@ dom/nodes/remove-and-adopt-thcrash.html:
   doesn't crash.
 dom/nodes/remove-next-sibling-during-replace-with.html:
 - remove-next-sibling-during-replace-with
-dom/nodes/rootNode.html:
-- getRootNode() must return context object's shadow-including root if options's composed
-  is true, and context object's root otherwise
 dom/ranges/Range-adopt-test.html:
 - 'Parentless range container moved to another document with appendChild: Removing
   the only element in the range must collapse the range'