Clean up session file optionality for --no-session (#3230)

crates/goose-bench/src/bench_session.rs

@@ -18,7 +18,7 @@ pub struct BenchAgentError {
 #[async_trait]
 pub trait BenchBaseSession: Send + Sync {
     async fn headless(&mut self, message: String) -> anyhow::Result<()>;
-    fn session_file(&self) -> PathBuf;
+    fn session_file(&self) -> Option<PathBuf>;
     fn message_history(&self) -> Vec<Message>;
     fn get_total_token_usage(&self) -> anyhow::Result<Option<i32>>;
 }
@@ -52,7 +52,7 @@ impl BenchAgent {
     pub(crate) async fn get_token_usage(&self) -> Option<i32> {
         self.session.get_total_token_usage().ok().flatten()
     }
-    pub(crate) fn session_file(&self) -> PathBuf {
+    pub(crate) fn session_file(&self) -> Option<PathBuf> {
         self.session.session_file()
     }
 }

crates/goose-bench/src/runners/eval_runner.rs

@@ -155,8 +155,15 @@ impl EvalRunner {
                 .canonicalize()
                 .context("Failed to canonicalize current directory path")?;
 
-            BenchmarkWorkDir::deep_copy(agent.session_file().as_path(), here.as_path(), false)
-                .context("Failed to copy session file to evaluation directory")?;
+            BenchmarkWorkDir::deep_copy(
+                agent
+                    .session_file()
+                    .expect("Failed to get session file")
+                    .as_path(),
+                here.as_path(),
+                false,
+            )
+            .context("Failed to copy session file to evaluation directory")?;
 
             tracing::info!("Evaluation completed successfully");
         } else {