CAMEL-23692: BacklogTracer captures late-arriving async branch events

[davsclaus]

Summary

• Fix BacklogTracer dropping trace events from async downstream routes (e.g., second branch of a multicast via Kafka/SEDA) when a new exchange claims the provisional history queue before the async branch finishes
• Add fallback clause that appends late events matching lastCompletedBreadcrumbId directly to completeHistoryQueue
• Add test BacklogTracerMessageHistoryMulticastSedaTest that reproduces the race condition

Test plan

• All 17 BacklogTracer* tests pass (no regressions)
• New test verifies multicast to two seda endpoints with delayed branch — all three routes appear in message history
• Manual verification with TUI History tab on a multi-route example using async endpoints

Claude Code on behalf of Claus Ibsen

🤖 Generated with Claude Code

[github-actions]

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