CAMEL-23945: Fix producer race on shared agent field (backport to 4.18.x)

[gnodet]

Claude Code on behalf of gnodet

Summary

Backport of the fix for CAMEL-23945 to the camel-4.18.x branch.

On main, the race condition in LangChain4jAgentProducer.process() was inadvertently fixed by commit 03d8361bbb7 (CAMEL-23697), which refactored the method to use a local variable. On camel-4.18.x, the original race still exists: agentFactory.createAgent(exchange) writes to the shared this.agent instance field, so concurrent exchanges can see each other's agents.

The race (before this PR)

if (agentFactory != null) {
    agent = agentFactory.createAgent(exchange);  // writes to shared field
}
AiAgentBody<?> aiAgentBody = agent.processBody(messagePayload, exchange);

Between the write and the read, another thread can overwrite this.agent with a different exchange's agent, causing the first exchange to use the wrong agent.

The fix

Agent agent = agentFactory != null ? agentFactory.createAgent(exchange) : this.agent;
AiAgentBody<?> aiAgentBody = agent.processBody(messagePayload, exchange);

A method-local variable ensures each exchange uses only its own factory-created agent.

Changes

• LangChain4jAgentProducer.java: Changed process() to use a local Agent agent variable instead of writing to the shared instance field
• LangChain4jAgentProducerConcurrencyTest.java: Added regression test that sends 50 concurrent exchanges through a single producer endpoint, each with a distinct factory-created agent. Verifies that every exchange receives the response from its own agent, not from another exchange's agent.

Test plan

• New LangChain4jAgentProducerConcurrencyTest passes (1 test)
• All existing unit tests in the module pass (7 total)
• CI green

🤖 Generated with Claude Code