Fix eval judging missing final response (#29638)

Fixed issue where eval thread judges were not considering the last
response in the thread.

The problem was that they were getting the full list of messages from
`last_request`, which (being a request!) did not have the response yet.

Release Notes:

- N/A

crates/agent/src/assistant.rs

@@ -41,7 +41,7 @@ use crate::assistant_configuration::{AddContextServerModal, ManageProfilesModal}
 pub use crate::assistant_panel::{AssistantPanel, ConcreteAssistantPanelDelegate};
 pub use crate::context::{ContextLoadResult, LoadedContext};
 pub use crate::inline_assistant::InlineAssistant;
-pub use crate::thread::{Message, Thread, ThreadEvent};
+pub use crate::thread::{Message, MessageSegment, Thread, ThreadEvent};
 pub use crate::thread_store::ThreadStore;
 pub use agent_diff::{AgentDiff, AgentDiffToolbar};