Restore thread cwd from owned settings snapshots (#41567)

## Why

Resuming a thread without an explicit `cwd` should restore that thread's latest
retained setting. Forked history can contain settings copied from another
thread, while compaction can move the latest setting outside the replay window.

## What changed

- Record the owning thread ID on new settings snapshots and only use snapshots
  owned by the resumed thread when restoring `cwd`. Older snapshots without an
  owner remain readable but do not override the startup `cwd`.
- Checkpoint the current settings after compaction and serialize checkpoints
  with settings updates so the retained history contains an accepted, current
  snapshot.
- Cover resume behavior across compaction, forks, reverts, legacy histories,
  and concurrent settings updates.

GitOrigin-RevId: 1efc9cf55472d6b88c465c4efe44672a232dbf64

codex-rs/core/src/session/turn_input.rs

@@ -129,6 +129,11 @@ impl PreparedTurnInputSettings {
             cyber_access_program,
         } = self.start_options;
         let emit_thread_settings_applied = self.thread_settings_update.is_some();
+        let _settings_guard = if emit_thread_settings_applied {
+            Some(thread_settings::acquire_persistence_lock(session).await)
+        } else {
+            None
+        };
         let mut updates = self.thread_settings_update.unwrap_or_default();
         updates.service_tier_for_turn = service_tier;