LoopDetectionMiddleware injected SystemMessage mid-conversation to warn
about repetitive tool calls. This crashes Anthropic models because
langchain_anthropic's _format_messages() requires system messages to
appear only at the start of the conversation — interleaved system
messages raise 'Received multiple non-consecutive system messages'.
Switch the warning injection from SystemMessage to HumanMessage, which
works with all providers (Anthropic, OpenAI, Google, etc.).
Fixes#1299
Co-authored-by: voidborne-d <voidborne-d@users.noreply.github.com>
67d8b64019