Clarify session exit messages (#40670)

## What changed

- Report `Session archived: <thread-id>` after successfully archiving the current session.
- Show the session ID when no resume hint is available, including for non-fatal exits.
- Keep deleted-thread exits distinct from successful archive exits.

## Testing

- Add coverage for archive lifecycle handling and exit-message formatting.

GitOrigin-RevId: 1812374e4c74fa1b3f11feb323de18a9dbff745b

codex-rs/cli/src/main.rs

@@ -790,9 +790,10 @@ fn handle_app_exit(exit_info: AppExitInfo) -> anyhow::Result<()> {
             eprintln!("ERROR: {message}");
             true
         }
-        ExitReason::UserRequested | ExitReason::TurnInterrupted | ExitReason::ThreadRemoved => {
-            false
-        }
+        ExitReason::UserRequested
+        | ExitReason::Archived(_)
+        | ExitReason::TurnInterrupted
+        | ExitReason::ThreadRemoved => false,
     };
 
     let update_action = exit_info.update_action;
@@ -3788,6 +3789,32 @@ mod tests {
         );
     }
 
+    #[test]
+    fn format_exit_messages_includes_session_id_without_resume_hint() {
+        let mut exit_info = sample_exit_info(
+            Some("123e4567-e89b-12d3-a456-426614174000"),
+            /*thread_name*/ None,
+        );
+        exit_info.token_usage = TokenUsage::default();
+        exit_info.resume_hint = None;
+        let lines = exit_info.format_exit_messages(/*color_enabled*/ false);
+        insta::assert_snapshot!(lines.join("\n"), @"Session ID: 123e4567-e89b-12d3-a456-426614174000");
+    }
+
+    #[test]
+    fn format_exit_messages_confirms_archive() {
+        let mut exit_info = sample_exit_info(
+            Some("123e4567-e89b-12d3-a456-426614174000"),
+            /*thread_name*/ None,
+        );
+        exit_info.exit_reason = ExitReason::Archived(exit_info.thread_id.unwrap());
+        let lines = exit_info.format_exit_messages(/*color_enabled*/ false);
+        insta::assert_snapshot!(lines.join("\n"), @"
+        Token usage: total=2 input=0 output=2
+        Session archived: 123e4567-e89b-12d3-a456-426614174000
+        ");
+    }
+
     #[test]
     fn format_exit_messages_includes_session_id_for_fatal_exit_without_resume_hint() {
         let exit_info = AppExitInfo {