return flatten axtree from playwright backend

Author: ollmer

src/agentlab/backends/browser/playwright.py

@@ -101,7 +101,9 @@ def page_screenshot(self):
         return Image.open(BytesIO(scr_bytes))
 
     def page_axtree(self):
-        return ""
+        axtree = self._loop.run_until_complete(self._page.accessibility.snapshot())
+        flat_axtree = flatten_axtree(axtree)
+        return flat_axtree
 
     def step(self, action: ToolCallAction):
         fn = self._actions[action.function.name]
@@ -126,3 +128,54 @@ def actions(self) -> tuple[ToolSpec]:
 
     def close(self):
         self._loop.run_until_complete(self._browser.close())
+
+
+def flatten_axtree(axtree_dict: dict | None) -> str:
+    """
+    Traverses accessibility tree dictionary and returns its markdown view.
+
+    Args:
+        axtree_dict: Accessibility tree from playwright page.accessibility.snapshot()
+                     Structure: dict with 'role', 'name', 'value', 'children' keys
+
+    Returns:
+        String representation of the accessibility tree in markdown format
+    """
+    if axtree_dict is None:
+        return ""
+
+    def traverse_node(node: dict, depth: int = 0) -> list[str]:
+        """Recursively traverse the accessibility tree and build markdown lines."""
+        lines = []
+        indent = "  " * depth  # 2 spaces per indent level
+
+        # Extract node information
+        role = node.get("role", "")
+        name = node.get("name", "")
+        value = node.get("value", "")
+
+        # Build the node representation
+        parts = []
+        if role:
+            parts.append(f"{role}:")
+        if name.strip():
+            parts.append(f"{name}")
+        if value:
+            parts.append(f"[value: {value}]")
+
+        # Only add line if there's meaningful content
+        if parts:
+            line = f"{indent}{' '.join(parts)}"
+            lines.append(line)
+
+        # Recursively process children
+        children = node.get("children", [])
+        for child in children:
+            child_lines = traverse_node(child, depth + 1)
+            lines.extend(child_lines)
+
+        return lines
+
+    # Start traversal from root
+    all_lines = traverse_node(axtree_dict, depth=0)
+    return "\n".join(all_lines)