fix(fastmcp): Remote MCP instrumentation (#3419)

Author: nina-kollman

packages/opentelemetry-instrumentation-mcp/opentelemetry/instrumentation/mcp/fastmcp_instrumentation.py

@@ -62,7 +62,6 @@ def traced_method(wrapped, instance, args, kwargs):
 
     def _fastmcp_tool_wrapper(self):
         """Create wrapper for FastMCP tool execution."""
-        @dont_throw
         async def traced_method(wrapped, instance, args, kwargs):
             if not self._tracer:
                 return await wrapped(*args, **kwargs)
@@ -111,13 +110,25 @@ async def traced_method(wrapped, instance, args, kwargs):
 
                     try:
                         result = await wrapped(*args, **kwargs)
+                    except Exception as e:
+                        tool_span.set_attribute(ERROR_TYPE, type(e).__name__)
+                        tool_span.record_exception(e)
+                        tool_span.set_status(Status(StatusCode.ERROR, str(e)))
 
+                        mcp_span.set_attribute(ERROR_TYPE, type(e).__name__)
+                        mcp_span.record_exception(e)
+                        mcp_span.set_status(Status(StatusCode.ERROR, str(e)))
+                        raise
+
+                    try:
                         # Add output in traceloop format to tool span
                         if self._should_send_prompts() and result:
                             try:
                                 # Convert FastMCP Content objects to serializable format
+                                # Note: result.content for fastmcp 2.12.2+, fallback to result for older versions
                                 output_data = []
-                                for item in result:
+                                result_items = result.content if hasattr(result, 'content') else result
+                                for item in result_items:
                                     if hasattr(item, 'text'):
                                         output_data.append({"type": "text", "content": item.text})
                                     elif hasattr(item, '__dict__'):
@@ -136,17 +147,9 @@ async def traced_method(wrapped, instance, args, kwargs):
 
                         tool_span.set_status(Status(StatusCode.OK))
                         mcp_span.set_status(Status(StatusCode.OK))
-                        return result
-
-                    except Exception as e:
-                        tool_span.set_attribute(ERROR_TYPE, type(e).__name__)
-                        tool_span.record_exception(e)
-                        tool_span.set_status(Status(StatusCode.ERROR, str(e)))
-
-                        mcp_span.set_attribute(ERROR_TYPE, type(e).__name__)
-                        mcp_span.record_exception(e)
-                        mcp_span.set_status(Status(StatusCode.ERROR, str(e)))
-                        raise
+                    except Exception:
+                        pass
+                    return result
 
         return traced_method