Add sorting/backwardsCursor to thread/list and new thread/turns/list api (#17305)

To improve performance of UI loads from the app, add two main
improvements:
1. The `thread/list` api now gets a `sortDirection` request field and a
`backwardsCursor` to the response, which lets you paginate forwards and
backwards from a window. This lets you fetch the first few items to
display immediately while you paginate to fill in history, then can
paginate "backwards" on future loads to catch up with any changes since
the last UI load without a full reload of the entire data set.
2. Added a new `thread/turns/list` api which also has sortDirection and
backwardsCursor for the same behavior as `thread/list`, allowing you the
same small-fetch for immediate display followed by background fill-in
and resync catchup.

codex-rs/state/src/model/mod.rs

@@ -28,6 +28,7 @@ pub use memories::Stage1StartupClaimParams;
 pub use thread_metadata::Anchor;
 pub use thread_metadata::BackfillStats;
 pub use thread_metadata::ExtractionOutcome;
+pub use thread_metadata::SortDirection;
 pub use thread_metadata::SortKey;
 pub use thread_metadata::ThreadMetadata;
 pub use thread_metadata::ThreadMetadataBuilder;

codex-rs/state/src/model/thread_metadata.rs

@@ -9,7 +9,6 @@ use codex_protocol::protocol::SessionSource;
 use sqlx::Row;
 use sqlx::sqlite::SqliteRow;
 use std::path::PathBuf;
-use uuid::Uuid;
 
 /// The sort key to use when listing threads.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -20,13 +19,18 @@ pub enum SortKey {
     UpdatedAt,
 }
 
+/// Sort direction to use when listing threads.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum SortDirection {
+    Asc,
+    Desc,
+}
+
 /// A pagination anchor used for keyset pagination.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Anchor {
     /// The timestamp component of the anchor.
     pub ts: DateTime<Utc>,
-    /// The UUID component of the anchor.
-    pub id: Uuid,
 }
 
 /// A single page of thread metadata results.
@@ -414,12 +418,11 @@ impl TryFrom<ThreadRow> for ThreadMetadata {
 }
 
 pub(crate) fn anchor_from_item(item: &ThreadMetadata, sort_key: SortKey) -> Option<Anchor> {
-    let id = Uuid::parse_str(&item.id.to_string()).ok()?;
     let ts = match sort_key {
         SortKey::CreatedAt => item.created_at,
         SortKey::UpdatedAt => item.updated_at,
     };
-    Some(Anchor { ts, id })
+    Some(Anchor { ts })
 }
 
 pub(crate) fn datetime_to_epoch_millis(dt: DateTime<Utc>) -> i64 {