fix(core): don't update the file's mtime on resume (#9553)

Remove `FileTimes::new().set_modified(SystemTime::now())` when resuming
a thread.

Context: It's awkward in UI built on top of app-server that resuming a
thread bumps the `updated_at` timestamp, even if no message is sent. So
if you open a thread (perhaps to just view its contents), it
automatically reorders it to the top which is almost certainly not what
you want.

codex-rs/core/src/rollout/recorder.rs

@@ -1,12 +1,10 @@
 //! Persist Codex session rollouts (.jsonl) so sessions can be replayed or inspected later.
 
 use std::fs::File;
-use std::fs::FileTimes;
 use std::fs::{self};
 use std::io::Error as IoError;
 use std::path::Path;
 use std::path::PathBuf;
-use std::time::SystemTime;
 
 use codex_protocol::ThreadId;
 use codex_protocol::models::BaseInstructions;
@@ -197,17 +195,14 @@ impl RolloutRecorder {
                     }),
                 )
             }
-            RolloutRecorderParams::Resume { path } => {
-                touch_rollout_file(&path)?;
-                (
-                    tokio::fs::OpenOptions::new()
-                        .append(true)
-                        .open(&path)
-                        .await?,
-                    path,
-                    None,
-                )
-            }
+            RolloutRecorderParams::Resume { path } => (
+                tokio::fs::OpenOptions::new()
+                    .append(true)
+                    .open(&path)
+                    .await?,
+                path,
+                None,
+            ),
         };
 
         // Clone the cwd for the spawned task to collect git info asynchronously
@@ -392,13 +387,6 @@ fn create_log_file(config: &Config, conversation_id: ThreadId) -> std::io::Resul
     })
 }
 
-fn touch_rollout_file(path: &Path) -> std::io::Result<()> {
-    let file = fs::OpenOptions::new().append(true).open(path)?;
-    let times = FileTimes::new().set_modified(SystemTime::now());
-    file.set_times(times)?;
-    Ok(())
-}
-
 async fn rollout_writer(
     file: tokio::fs::File,
     mut rx: mpsc::Receiver<RolloutCmd>,