Add LLM::{Conversation,LazyConversation}#last_message

[0x1eef]

This new method provides a short-hand way to reference the
most recent message in a conversation, with an option to filter
by the role of a message as well.

For example:

message = conversation.last_message
message = conversation.last_message(role: 'assistant') 
message = conversation.last_message(role: 'user')

It is also aliased as recent_message

message = conversation.recent_message
message = conversation.recent_message(role: 'assistant') 
message = conversation.recent_message(role: 'user')

[Copilot]

Pull Request Overview

This PR introduces a new shorthand method for retrieving the last message in a conversation, with optional filtering by role, and provides an alias for the method. Key changes include:

• Adding tests to verify the behavior of last_message (and its alias recent_message) in LazyConversation.
• Implementing last_message and recent_message in both Conversation and LazyConversation classes.
• Defining the assistant_role method for various providers with slight variations based on provider-specific API expectations.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
spec/llm/lazy_conversation_spec.rb	Adds specs for the last_message method for different roles in conversation testing.
lib/llm/providers/openai.rb	Implements assistant_role returning "assistant".
lib/llm/providers/ollama.rb	Implements assistant_role returning "assistant".
lib/llm/providers/gemini.rb	Implements assistant_role returning "model" (diverging from other providers).
lib/llm/providers/anthropic.rb	Implements assistant_role returning "assistant".
lib/llm/provider.rb	Adds an abstract assistant_role method to enforce implementation in providers.
lib/llm/message.rb	Ensures roles are stored as strings by converting the given role to a string.
lib/llm/lazy_conversation.rb	Adds last_message (and alias recent_message) to retrieve the last message by role.
lib/llm/conversation.rb	Adds last_message (and alias recent_message) similar to LazyConversation.

Comments suppressed due to low confidence (2)

lib/llm/providers/gemini.rb:50

• [nitpick] The assistant_role method returns 'model' here, which differs from other providers returning 'assistant'. Confirm that this is intentional for the Gemini provider to reflect its API behavior.

      "model"

spec/llm/lazy_conversation_spec.rb:35

• [nitpick] The test expects an assistant message with role 'model' in this context. Please verify that the intended provider configuration is being used so that this expectation aligns correctly with the provider's assistant_role value.

              role: "model",