fix(anthropic): use non-whitespace trailing dummy to satisfy provider validation#6216
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…space placeholder The trailing user message injected for Claude 4.6+ (which does not support prefilling) used a single space, which Anthropic's API rejects with: HTTP 400 invalid_request_error "messages: text content blocks must contain non-whitespace text" This stalled any LiveKit agent on claude-sonnet-4-6 / claude-opus-4-6 whenever the chat_ctx ended on an assistant turn (sequential generate_reply, agent handoff, etc.). Use "." instead — minimal-blast-radius placeholder that preserves the intent of PR livekit#4973 while satisfying Anthropic's validator. Refs: livekit#6213 Related: livekit#4973, livekit#4907
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Summary
One-line fix in
livekit-agents/livekit/agents/llm/_provider_format/anthropic.py: the trailing dummy user message injected when the last message is from the assistant now uses"."instead of" "(a single non-whitespace character instead of whitespace).Why
Anthropic's API rejects messages whose text content is empty or whitespace-only. When
inject_trailing_user_message=Trueappends a placeholder user turn to satisfy Claude 4.6+'s no-prefilling requirement, the current" "(single space) trips Anthropic's server-side validation and the request fails before the model is ever reached. Replacing it with"."keeps the placeholder semantically inert while clearing the validation gate.Relationship to existing issues
This addresses #5254, which was closed as stale. The bug still reproduces verbatim on current
main(1.6.3) — any conversation that ends with an assistant turn and is then re-submitted to the Anthropic provider hits the same validation error described in the original report.Requesting reopen of #5254 and merge of this fix.
Change
That is the entire diff.