🐛 fix(observability): wire OpenTelemetry propagator + nest async event handlers

 Axon's `OpenTelemetryAutoConfiguration` (4.13) builds `OpenTelemetrySpanFactory.builder().build()` without injecting Spring's `OpenTelemetry` bean, falling back to `GlobalOpenTelemetry` — which is no-op when using
     `micrometer-tracing-bridge-otel`. Result: silent context loss across async boundaries.

     - `TracingConfiguration`: explicit `tracer` + `contextPropagators` from Micrometer-managed `OpenTelemetry`
     - `application.yaml`: `axon.tracing.event-processor.distributed-in-same-trace: true` so pooled processors join the originating trace within the time limit

Author: MateuszNaKodach

src/main/java/com/dddheroes/heroesofddd/shared/infrastructure/TracingConfiguration.java

@@ -12,8 +12,13 @@ class TracingConfiguration {
 
     @Bean
     OpenTelemetrySpanFactory openTelemetrySpanFactory(OpenTelemetry openTelemetry) {
+        // Both tracer AND propagator must come from the same Micrometer-managed OpenTelemetry —
+        // otherwise the Builder falls back to no-op GlobalOpenTelemetry.getPropagators() and
+        // propagateContext() / createHandlerSpan() silently lose the W3C trace context across
+        // async boundaries (event processors, deadlines, Axon Server gRPC).
         return OpenTelemetrySpanFactory.builder()
                 .tracer(openTelemetry.getTracer("axon-framework"))
+                .contextPropagators(openTelemetry.getPropagators().getTextMapPropagator())
                 .build();
     }
 }

src/main/resources/application.yaml

@@ -70,6 +70,11 @@ axon:
   tracing:
     # All Axon attribute providers stay at their defaults (true)
     show-event-sourcing-handlers: false
+    event-processor:
+      # Nest async (StreamingEventProcessor / pooled) event handler spans into the trace
+      # that published the event, when handled within the time limit below. Off by default.
+      distributed-in-same-trace: true
+      distributed-in-same-trace-time-limit: 2m
 #  update-check:
 #    disabled: true