Fix flakey resume test (#9789)

Sessions' `updated_at` times are truncated to seconds, with the UUID
session ID used to break ties. If the two test sessions are created in
the same second, AND the session B UUID < session A UUID, the test
fails.

Fix this by mutating the session mtimes, from which we derive the
updated_at time, to ensure session B is updated_at later than session A.

codex-rs/exec/tests/suite/resume.rs

@@ -4,7 +4,11 @@ use codex_utils_cargo_bin::find_resource;
 use core_test_support::test_codex_exec::test_codex_exec;
 use pretty_assertions::assert_eq;
 use serde_json::Value;
+use std::fs::FileTimes;
+use std::fs::OpenOptions;
 use std::string::ToString;
+use std::time::Duration;
+use std::time::SystemTime;
 use tempfile::TempDir;
 use uuid::Uuid;
 use walkdir::WalkDir;
@@ -258,6 +262,17 @@ fn exec_resume_last_respects_cwd_filter_and_all_flag() -> anyhow::Result<()> {
     let path_b = find_session_file_containing_marker(&sessions_dir, &marker_b)
         .expect("no session file found for marker_b");
 
+    // Files are ordered by `updated_at`, then by `uuid`.
+    // We mutate the mtimes to ensure file_b is the newest file.
+    let file_a = OpenOptions::new().write(true).open(&path_a)?;
+    file_a.set_times(
+        FileTimes::new().set_modified(SystemTime::UNIX_EPOCH + Duration::from_secs(1)),
+    )?;
+    let file_b = OpenOptions::new().write(true).open(&path_b)?;
+    file_b.set_times(
+        FileTimes::new().set_modified(SystemTime::UNIX_EPOCH + Duration::from_secs(2)),
+    )?;
+
     let marker_b2 = format!("resume-cwd-b-2-{}", Uuid::new_v4());
     let prompt_b2 = format!("echo {marker_b2}");
     test.cmd()