Add persisted manual ordering for thread sections (#36007)

## What changed

- Add `thread/section/move` to atomically move a thread into, within, or out of a section. Threads can be inserted before an existing member or appended, and moves within a section preserve `sectionEnteredAt`.
- Add `section_position` sorting to `thread/list`, with ascending order as its default, and expose `sectionEnteredAt` in thread responses.
- Persist section positions and entry times in SQLite, including migration of existing section members into recency order. Section membership is no longer updated through `thread/metadata/update`.

## Testing

- Cover section moves, reordering, pagination, persistence across restarts and rollout reconciliation, concurrent updates, and rank renumbering.

GitOrigin-RevId: aec6d7ddedca5277029b5caf5c074975397e956c

codex-rs/core/src/realtime_context_tests.rs

@@ -53,6 +53,8 @@ fn stored_thread(cwd: &str, title: &str, first_user_message: &str) -> StoredThre
             .expect("valid timestamp"),
         archived_at: None,
         section: None,
+        section_position: None,
+        section_entered_at: None,
         cwd: PathBuf::from(cwd),
         cli_version: "test".to_string(),
         source: SessionSource::Cli,

codex-rs/core/src/thread_manager.rs

@@ -72,6 +72,7 @@ use codex_thread_store::InMemoryThreadStore;
 use codex_thread_store::LoadThreadHistoryParams;
 use codex_thread_store::LocalThreadStore;
 use codex_thread_store::LocalThreadStoreConfig;
+use codex_thread_store::MoveThreadToSectionParams;
 use codex_thread_store::PreparedFork;
 use codex_thread_store::ReadThreadByRolloutPathParams;
 use codex_thread_store::ReadThreadParams;
@@ -730,6 +731,32 @@ impl ThreadManager {
             })
     }
 
+    /// Moves a persisted thread to, within, or out of a server-ordered section.
+    pub async fn move_thread_to_section(
+        &self,
+        thread_id: ThreadId,
+        section: Option<&str>,
+        before_thread_id: Option<ThreadId>,
+    ) -> CodexResult<()> {
+        if let Ok(thread) = self.get_thread(thread_id).await
+            && thread.config_snapshot().await.ephemeral
+        {
+            return Err(CodexErr::InvalidRequest(format!(
+                "ephemeral thread does not support section moves: {thread_id}"
+            )));
+        }
+
+        self.state
+            .thread_store
+            .move_thread_to_section(MoveThreadToSectionParams {
+                thread_id,
+                section: section.map(ToOwned::to_owned),
+                before_thread_id,
+            })
+            .await
+            .map_err(|err| thread_store_metadata_update_error(thread_id, err))
+    }
+
     /// List `thread_id` plus all known descendants in its spawn subtree.
     pub async fn list_agent_subtree_thread_ids(
         &self,