fix(tools): correct Grok response parsing for xAI Responses API (#13049)

* fix(tools): correct Grok response parsing for xAI Responses API

The xAI Responses API returns content in output[0].content[0].text,
not in output_text field. Updated GrokSearchResponse type and
runGrokSearch to extract content from the correct path.

Fixes the 'No response' issue when using Grok web search.

* fix(tools): harden Grok web_search parsing (#13049) (thanks @ereid7)

---------

Co-authored-by: erai <erai@erais-Mac-mini.local>
Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

src/agents/tools/web-search.test.ts

@@ -10,6 +10,7 @@ const {
   resolveGrokApiKey,
   resolveGrokModel,
   resolveGrokInlineCitations,
+  extractGrokContent,
 } = __testing;
 
 describe("web_search perplexity baseUrl defaults", () => {
@@ -142,3 +143,23 @@ describe("web_search grok config resolution", () => {
     expect(resolveGrokInlineCitations({ inlineCitations: false })).toBe(false);
   });
 });
+
+describe("web_search grok response parsing", () => {
+  it("extracts content from Responses API output blocks", () => {
+    expect(
+      extractGrokContent({
+        output: [
+          {
+            content: [{ text: "hello from output" }],
+          },
+        ],
+      }),
+    ).toBe("hello from output");
+  });
+
+  it("falls back to deprecated output_text", () => {
+    expect(extractGrokContent({ output_text: "hello from output_text" })).toBe(
+      "hello from output_text",
+    );
+  });
+});