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/app-server/src/request_processors/thread_processor.rs

@@ -3739,7 +3739,21 @@ impl ThreadRequestProcessor {
             };
         }
 
-        let history_cwd = thread_history.session_cwd();
+        // Copied or referenced history can contain another thread's settings. Only snapshots
+        // explicitly owned by this thread can override its startup cwd.
+        let history_cwd = if let InitialHistory::Resumed(resumed) = &thread_history {
+            resumed.history.iter().rev().find_map(|item| match item {
+                RolloutItem::EventMsg(EventMsg::ThreadSettingsApplied(event))
+                    if event.thread_id == Some(resumed.conversation_id) =>
+                {
+                    Some(event.thread_settings.cwd.to_path_buf())
+                }
+                _ => None,
+            })
+        } else {
+            None
+        };
+        let history_cwd = history_cwd.or_else(|| thread_history.session_cwd());
         let runtime_workspace_roots = runtime_workspace_roots.map(resolve_runtime_workspace_roots);
         let mut typesafe_overrides = self.build_thread_config_overrides(
             model,