Continuum Provider Error: Conversation roles must alternate

[AnthonyRonning]

Investigation into logs reveals an error from the Continuum provider:
Provider continuum returned status 400 Bad Request: {"error":{"message":"Conversation roles must alternate user/assistant/user/assistant/... Conversation roles must alternate user/assistant/user/assistant/...","type":"BadRequestError","param":null,"code":400}}

Context:

• Occurred in opensecret::web::openai.
• Model: gemma-3-27b.
• Timestamp: 2025-11-22T19:44:57.126061Z.

Possible causes:

• src/web/responses/handlers.rs or build_prompt logic constructing invalid message history.
• Consecutive messages from the same role being sent to a model that enforces strict alternation.

We should investigate build_prompt and ensure message history complies with provider requirements.