turns.md
In ellmer: Chat with Large Language Models

normalize_turns throws useful errors

Code
  normalize_turns(1)
Condition
  Error:
  ! `turns` must be an unnamed list or `NULL`, not the number 1.
Code
  normalize_turns(list(1))
Condition
  Error in `normalize_turns()`:
  ! Every element of `turns` must be a `turn`.
Code
  normalize_turns(list(sys_msg, user_msg), 1)
Condition
  Error:
  ! `system_prompt` must be a character vector or `NULL`, not the number 1.
Code
  normalize_turns(list(sys_msg, user_msg), "foo2")
Condition
  Error:
  ! `system_prompt` and `turns[[1]]` can't contain conflicting system prompts.