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fix: move handoff instructions to system prompt (fixes #54) - #58
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… after tool" API error When the receiving agent's filtered messages end with a ToolMessage (e.g. from list_upload_sessions before the handoff), appending handoff instructions as a HumanMessage produced the sequence tool → user, which many chat APIs reject (400 Unexpected role 'user' after role 'tool'). Now we extend the last ToolMessage's content with the instructions instead, so the next turn is validly an assistant response.
…ssage
Replaces the approach of appending instructions as a HumanMessage (or
extending ToolMessage content) with system prompt injection through the
existing AgentContext.setHandoffContext → buildIdentityPreamble pipeline.
This fixes the "400 Unexpected role 'user' after role 'tool'" error
(issue #54) that occurred when a router agent ran a non-handoff tool
before handing off. After filtering transfer messages, the last message
was a ToolMessage, and appending a HumanMessage created an invalid
tool → user role sequence.
By moving instructions into the system prompt (## Task Instructions),
role ordering is never affected regardless of what the last filtered
message is
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…ystem prompt) Revert PR LibreChat-AI#55 approach (inject instructions into last ToolMessage) and restore upstream fix from LibreChat-AI#58: handoff instructions are injected into the system prompt via AgentContext.setHandoffContext and buildIdentityPreamble. This avoids the bridge AIMessage and the '400 Unexpected role user after role tool' API error (issue LibreChat-AI#54). Co-authored-by: Cursor <cursoragent@cursor.com>
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