Hi, everyone! I noticed, that when an application adds its own middleware to a Symfony Messenger bus, OpenTelemetry middleware from the bundle is no longer registered. For example, this configuration removes OpenTelemetry middleware from the resulting middleware stack:

framework:
    messenger:
        buses:
            messenger.bus.default:
                middleware:
                    - App\Messenger\Middleware\CustomMiddleware

The problem is that Symfony does not deep merge the middleware option. Right now the bundle prepends its middleware through FrameworkBundle configuration, but application configuration replaces the prepended middleware list.

I propose moving OpenTelemetry middleware registration to a compiler pass. The compiler pass will update the middleware stack after FrameworkBundle has normalized Messenger configuration, but before Symfony builds the buses.

With this change application middleware will be preserved, tracing and metrics middleware will be added before send_message and handle_message, and the configured default_bus will still be respected. Manually configured OpenTelemetry middleware will also not be added twice.