crewAI: System messages with None or list content are stringified into the prompt (OpenAI o1 path, Anthropic)

Finding: In a reporter-supplied reproduction on crewAI main at commit 6b93fa0 (reported as 1.15.27, Python 3.12), system messages whose content is None or a list of content parts are stringified instead of being handled as content, in the native OpenAI o1 path and in the Anthropic provider (https://github.com/crewAIInc/crewAI/issues/8038). This is an external report; it has not been reproduced by KFA and no maintainer has confirmed it in the supplied context. Reported symptoms: For OpenAICompletion._format_messages with an o1 model, the system message is rewritten using an f-string around the content. A None content gives a user message reading 'System: None', and list content gives 'System: ' followed by a Python list repr. For AnthropicCompletion._format_messages_for_anthropic, a later None system message appends the text 'None' to the system string. When the first system message is a list, string concatenation with += extends that list with the characters of the following strings, so the resulting system value mixes a content block and bare strings. The reporter says the Anthropic API would reject such a value, but that rejection is not shown in the issue and no exact error message was supplied. Reporter-stated cause: Both system-message paths assume str content, although LLMMessage.content is typed as str | list[dict] | None. The reporter says user and assistant messages already handle all three shapes, and that the scope is limited to the two system-message paths. Expected behavior per the reporter: None contributes nothing, and list content contributes its text parts or is passed through as blocks where the API supports it, so the system prompt never contains 'None', a list repr, or bare strings inside a block list. Status: The issue is open. The reporter offers a fix PR after confirmation. No fix commit, release, or workaround is cited in the supplied sources. Practical diagnosis, if you are affected: check whether any code builds system messages with None or list-of-parts content and goes through these providers. Treat that as a hypothesis to test, not a confirmed workaround. Evidence is a single external report with printed outputs; no independent reproduction is available.