fix(mcp): preserve structured_content in tool call results

MCP CallToolResult may include structured_content (a JSON object) alongside
content blocks. The tool handler previously only forwarded concatenated text
from content blocks, silently dropping the structured payload.

This breaks MCP tools that return a minimal human text in content while
putting the actual machine-usable payload in structured_content.

Now, when structured_content is present, it is included in the returned
JSON under the 'structuredContent' key.

Fixes NousResearch/hermes-agent#5874

tools/mcp_tool.py

@@ -1253,7 +1253,16 @@ def _make_tool_handler(server_name: str, tool_name: str, tool_timeout: float):
             for block in (result.content or []):
                 if hasattr(block, "text"):
                     parts.append(block.text)
-            return json.dumps({"result": "\n".join(parts) if parts else ""})
+            text_result = "\n".join(parts) if parts else ""
+
+            # Preserve structured_content (structuredContent) if present
+            structured = getattr(result, "structured_content", None)
+            if structured is not None:
+                return json.dumps({
+                    "result": text_result,
+                    "structuredContent": structured,
+                })
+            return json.dumps({"result": text_result})
 
         try:
             return _run_on_mcp_loop(_call(), timeout=tool_timeout)