Add PerplexityLLMAdapter for message ordering strictness#4009
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…straints Perplexity's API is stricter than OpenAI about conversation history: - Requires strict alternation between user/tool and assistant messages - Disallows system messages except as the initial message - Requires the last message to be user or tool The new adapter transforms messages before sending to satisfy all three constraints: merging consecutive initial system messages, converting non-initial system to user, merging consecutive same-role messages, and removing trailing assistant messages. Also adds dual-system-instruction warnings to Cerebras, Fireworks, Mistral, Perplexity, and SambaNova services (matching the existing BaseOpenAILLMService pattern), and updates the warning text in BaseOpenAILLMService to be more descriptive.
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Perplexity allows multiple initial system messages, so don't merge them. Instead, skip system-system pairs during the consecutive same-role merge step. Broaden the trailing message fix to convert any trailing system message to user (not just a lone system message), so contexts with only system messages don't fail.
Add test exercising the step 3 ordering where stripping a trailing assistant exposes a system message that then gets converted to user. Move the reasoning about when a trailing system message can occur into the docstring.
Perplexity appears to have statefulness within a conversation, so converting a system message to "user" in one call and then back to "system" in the next (after more messages are appended) causes API errors. Remove the trailing system→user conversion entirely — if the context only has system messages, the API call will fail but the mistake will be caught right away.
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aconchillo
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LGTM! |
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Summary
PerplexityLLMAdapterthat transforms conversation messages to satisfy Perplexity's stricter API constraints before sending requests. Perplexity requires strict role alternation (user/tool ↔ assistant), no non-initial system messages, and the last message to be user/tool — conversation histories that work fine with OpenAI can cause errors with Perplexity (PerplexityLLMServicesubclassesOpenAILLMService).PerplexityLLMServicenow uses this adapter viaadapter_class = PerplexityLLMAdapter.BaseOpenAILLMServicebehavior.Testing
11 test cases cover: standard passthrough, initial system preservation, multiple initial system preservation, consecutive same-role merging, non-initial system conversion, trailing assistant removal, system-only context preserved, system exposed after trailing assistant removal, consecutive assistant merge+removal, tool message preservation, and empty messages.
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