fix: propagate app_user_email when global context already exists

When invoke_tool receives an existing plugin_global_context from middleware,
the user email was not being propagated to the global context. This caused
plugins to receive user: null in their GlobalContext.

This fix ensures the user email is always propagated to the global context
when available, enabling security plugins to properly track which user
made each request.

Closes #1550
Supersedes #1551

Co-authored-by: Ilia Manolov <iliamanolov@outlook.com>
Signed-off-by: Mihai Criveti <crivetimihai@gmail.com>

Author: crivetimihai

mcpgateway/services/tool_service.py

@@ -1466,6 +1466,9 @@ async def invoke_tool(
             gateway_id = getattr(tool, "gateway_id", None)
             if gateway_id and isinstance(gateway_id, str):
                 global_context.server_id = gateway_id
+            # Propagate user email to global context for plugin access
+            if app_user_email and isinstance(app_user_email, str):
+                global_context.user = app_user_email
         else:
             # Create new context (fallback when middleware didn't run)
             # Use correlation ID from context if available, otherwise generate new one