fix: reconcile typed history with run exits

crates/agen/tests/engine_fixtures.rs

@@ -9,8 +9,8 @@ use std::path::Path;
 use std::sync::Arc;
 use std::sync::atomic::{AtomicUsize, Ordering};
 
+use agen::Engine;
 use agen::tool::{Tool, ToolDefinition, ToolError, ToolMeta, ToolOutput};
-use agen::{Engine, History};
 use async_trait::async_trait;
 use common::MockLlmClient;
 
@@ -134,7 +134,7 @@ async fn test_engine_simple_text_response() {
 
     let client = MockLlmClient::from_fixture(&fixture_path).unwrap();
     let engine = Engine::new(client);
-    let mut history: History = History::new();
+    let mut history = agen::History::new();
 
     // Send a simple message (Mutable::run consumes self, returns tuple)
     let result = engine.run(&mut history, "Hello").await;
@@ -160,7 +160,7 @@ async fn test_engine_tool_call() {
 
     let client = MockLlmClient::from_fixture(&fixture_path).unwrap();
     let mut engine = Engine::new(client);
-    let mut history: History = History::new();
+    let mut history = agen::History::new();
 
     // Register tool
     let weather_tool = MockWeatherTool::new();
@@ -202,7 +202,7 @@ async fn test_engine_with_programmatic_events() {
 
     let client = MockLlmClient::new(events);
     let engine = Engine::new(client);
-    let mut history: History = History::new();
+    let mut history = agen::History::new();
 
     // Mutable::run consumes self, returns tuple
     let result = engine.run(&mut history, "Greet me").await;