🛡️ fix: validate edge agent refs early in MultiAgentGraph#111
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danny-avila merged 1 commit intomainfrom Apr 19, 2026
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🛡️ fix: validate edge agent refs early in MultiAgentGraph#111danny-avila merged 1 commit intomainfrom
danny-avila merged 1 commit intomainfrom
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Adds a `validateEdgeAgents()` check in the `MultiAgentGraph` constructor that throws a descriptive error when any edge (on `from` or `to`) points at an agent not present in `agentContexts`. Without this guard, `StateGraph.compile()` later throws the opaque `Found edge ending at unknown node "<id>"` error that gives callers no indication of why — this was the surface error from LibreChat's #12726 where the host passed `edges` into a multi-agent run without also loading the sub-agents. The new error explicitly instructs callers to include every referenced agent or filter orphaned edges upstream.
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Adds a `validateEdgeAgents()` check in the `MultiAgentGraph` constructor that throws a descriptive error when any edge (on `from` or `to`) points at an agent not present in `agentContexts`. Without this guard, `StateGraph.compile()` later throws the opaque `Found edge ending at unknown node "<id>"` error that gives callers no indication of why — this was the surface error from LibreChat's #12726 where the host passed `edges` into a multi-agent run without also loading the sub-agents. The new error explicitly instructs callers to include every referenced agent or filter orphaned edges upstream.
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Summary
Safety-net fix for the root failure mode seen in LibreChat #12726: when a host passes
edgesinto amulti-agentrun without including every referenced agent inagents,StateGraph.compile()throws the opaqueFound edge ending at unknown node "<id>"error — with no indication that the true cause is a missing agent config.This change validates the edges up-front in the
MultiAgentGraphconstructor and throws a descriptive error naming every missing agent id, pointing callers at the real fix (include the agent or filter the orphan edge).Why in the SDK as well as the host?
LibreChat's own controllers now pre-load handoff sub-agents (see the companion PR), so this SDK guard is not load-bearing for the LibreChat bug. It's here because the same class of mistake is easy for any downstream consumer to make, and the LangGraph error message gives them nothing actionable. Failing fast with a clear message saves the next person a long debugging session.
Test plan
src/graphs/__tests__/MultiAgentGraph.test.ts— 6 cases covering valid graphs, unknownto, unknownfrom, multiple unknowns reported together, array-formfrom/to, and empty-edges case.npx jest src/graphs/__tests__/MultiAgentGraph.test.ts.npx tsc --noEmitclean.