pipecat/changelog/4009.added.md

• Added PerplexityLLMAdapter that automatically transforms conversation messages to satisfy Perplexity's stricter API constraints (strict role alternation, no non-initial system messages, last message must be user/tool). Previously, certain conversation histories could cause Perplexity API errors that didn't occur with OpenAI (PerplexityLLMService subclasses OpenAILLMService since Perplexity uses an OpenAI-compatible API).