You delegate a task from Agent A to Agent B in LangChain. Agent B fails. Agent A's callback chain fires 'success' anyway.
This is the observability blind spot most builders miss in agentic workflows: delegation masking. A sub-agent fails silently, but the parent agent's callback layer never knows because it only watches the delegation call itself, not what the delegated agent actually did.
Let's walk the mechanism.
The Delegation Pattern in LangChain
When you wire up agent-to-agent delegation in LangChain, you're typically using the tool decorator to wrap a sub-agent invocation:
