CAMEL-23299: propagate transacted flag in AggregateProcessor for synchronous executor

[Croway]

Backport of #22511 to main.

Summary

• Exchange.copy() does not preserve the transacted flag. When the aggregate uses SynchronousExecutorService, the completion runs on the caller thread and can legitimately be transactional
• Propagate the flag on the correlated copy so Pipeline.process() uses scheduleQueue instead of scheduleMain, avoiding a queue-swap deadlock in the reactive executor's executeFromQueue loop
• Mirrors the same pattern already used by the Splitter (line 216)

Test plan

• SplitAggregateDirectRouteTransactedDeadlockTest — transacted split + aggregate routed to a separate direct: route (deadlocked before, passes now)
• SplitAggregateInChoiceSynchronousExecutorTest — existing CAMEL-23281 tests still pass
• SplitAggregateSynchronousExecutorStackOverflowIssueTest — CAMEL-23030 regression guard still passes

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[gnodet]

Nice fix, Federico — clean and well-targeted. A couple of observations:

Missing TRANSACTION_CONTEXT_DATA propagation?

The Splitter (line 216–219), MulticastProcessor (line 980–983), and RecipientListProcessor (line 309–312) all follow a two-step pattern after createCorrelatedCopy:

copy.getExchangeExtension().setTransacted(exchange.isTransacted());
if (exchange.isTransacted() && copy.getProperty(Exchange.TRANSACTION_CONTEXT_DATA) == null) {
    copy.setProperty(Exchange.TRANSACTION_CONTEXT_DATA, ...);
}

This PR only does step 1 (setting the transacted flag) but not step 2 (propagating TRANSACTION_CONTEXT_DATA). For the specific deadlock fix with manually-transacted exchanges this is fine, but in scenarios with a real transaction manager, the missing context data could cause issues downstream. Is this intentionally scoped differently or an oversight?

Minor: JIRA link

The PR body references CAMEL-23281 and CAMEL-23030 but doesn't include a direct link to CAMEL-23299 at the top.

Otherwise the fix looks good — well-commented, properly guarded for SynchronousExecutorService, and the test coverage with @Timeout(30) is solid for deadlock reproducers.

Claude Code on behalf of Guillaume Nodet

[Croway]

good point @gnodet I'll add the TRANSACTION_CONTEXT_DATA handling