Expose model metadata from each thread's catalog and settings (#59958)

## What changed

- Add `ThreadManager::models_manager_for_startup` to obtain the model catalog used when starting or cold-resuming a root thread, including its effective originator.
- Add `CodexThread::selected_model_info` to resolve the model for future turns using the thread's current settings, catalog, and model overrides.
- Share catalog selection logic between startup lookup and thread creation.

## Testing

Add coverage verifying that startup and thread lookups use the thread-specific catalog, preserve the configured context window, and reflect model selection updates.

GitOrigin-RevId: d7976caebb7459e1e9ca55f3c6f6bb2af92cf3de

codex-rs/core/src/codex_thread.rs

@@ -41,6 +41,7 @@ use codex_protocol::models::ActivePermissionProfile;
 use codex_protocol::models::PermissionProfile;
 use codex_protocol::models::ProfileWorkspaceRoot;
 use codex_protocol::models::ResponseItem;
+use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ReasoningEffort;
 use codex_protocol::protocol::AskForApproval;
 use codex_protocol::protocol::EnvironmentConfig;
@@ -1146,6 +1147,11 @@ impl CodexThread {
         self.session.state_db()
     }
 
+    /// Resolves the model selected for future turns using this thread's catalog and settings.
+    pub async fn selected_model_info(&self) -> Arc<ModelInfo> {
+        self.session.selected_model_info().await
+    }
+
     pub async fn config_snapshot(&self) -> ThreadConfigSnapshot {
         self.session.thread_config_snapshot().await
     }