feat(webmcp): add UntrustedContent annotation support (#3442)

Ports upstream puppeteer PR #14901 which adds `untrustedContent` to
WebMCPAnnotation, indicating tool output may contain untrusted content
such as UGC or 3rd-party data.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: kblok

lib/PuppeteerSharp.Tests/WebMcpTests/PageWebMcpTests.cs

@@ -39,8 +39,10 @@ await page.EvaluateFunctionAsync(@"() => {
                     name: 'test-tool-1',
                     description: 'A test tool 1',
                     inputSchema: { type: 'object', properties: { text: { type: 'string' } }, required: ['text'] },
-                    execute: () => {},
-                    annotations: { readOnlyHint: true },
+                    execute: (params) => {
+                        return params.text;
+                    },
+                    annotations: { readOnlyHint: true, untrustedContentHint: true },
                 });
             }");
 
@@ -55,6 +57,9 @@ await page.EvaluateFunctionAsync(@"() => {
 
             var tools = page.WebMcp.Tools();
             Assert.That(tools.Length, Is.GreaterThanOrEqualTo(2));
+            Assert.That(tools[0].Annotations, Is.Not.Null);
+            Assert.That(tools[0].Annotations!.ReadOnly, Is.True);
+            Assert.That(tools[0].Annotations!.UntrustedContent, Is.True);
         }
 
         [Test, PuppeteerTest("webmcp.spec", "Page.webmcp", "should fire toolsadded events")]

lib/PuppeteerSharp/Cdp/CdpWebMcp.cs

@@ -164,6 +164,7 @@ private void OnToolsAdded(WebMcpToolsAddedProtocolEvent e)
                 Annotations = tool.Annotations == null ? null : new WebMcpAnnotation
                 {
                     ReadOnly = tool.Annotations.ReadOnly,
+                    UntrustedContent = tool.Annotations.UntrustedContent,
                     Autosubmit = tool.Annotations.Autosubmit,
                 },
                 Frame = frame,
@@ -306,6 +307,9 @@ private class WebMcpProtocolAnnotation
 
         [JsonPropertyName("readOnly")]
         public bool? ReadOnly { get; set; }
+
+        [JsonPropertyName("untrustedContent")]
+        public bool? UntrustedContent { get; set; }
     }
 
     private class WebMcpProtocolRemovedTool

lib/PuppeteerSharp/Cdp/WebMcpAnnotation.cs

@@ -32,6 +32,11 @@ public class WebMcpAnnotation
     /// </summary>
     public bool? ReadOnly { get; set; }
 
+    /// <summary>
+    /// A hint indicating that the tool output may contain untrusted content, ex: UGC, 3rd party data.
+    /// </summary>
+    public bool? UntrustedContent { get; set; }
+
     /// <summary>
     /// If the declarative tool was declared with the autosubmit attribute.
     /// </summary>