@spec add_messages([t()], [instruction()] | instruction()) :: [t()]

Reducer that folds a list of instructions onto the existing history.

Instructions are applied left to right:

• a plain message is appended, or replaces an existing one when their :id values match (corrections/updates)
• a RemoveMessage with a matching :id deletes that message
• the remove_all/0 sentinel clears everything accumulated so far, so a node can replace the whole history in a single update

Order matters: [remove_all(), summary] clears the history and keeps summary, while [summary, remove_all()] would discard summary too.

@spec ai(
  String.t(),
  keyword()
) :: LangEx.Message.AI.t()

Create an AI message.

@spec human(
  String.t(),
  keyword()
) :: LangEx.Message.Human.t()

Create a human message.

@spec remove(String.t()) :: LangEx.Message.RemoveMessage.t()

Create a RemoveMessage targeting a single message by its :id.

@spec remove_all() :: LangEx.Message.RemoveMessage.t()

Create a RemoveMessage that clears the entire prior history.

@spec system(
  String.t(),
  keyword()
) :: LangEx.Message.System.t()

Create a system message.

@spec tool(String.t(), String.t(), keyword()) :: LangEx.Message.Tool.t()

Create a tool result message.