ThreadStore interface (#17659)

Introduce a ThreadStore interface for mediating access to the filesystem
(rollout jsonl files + sqlite db) based thread storage.

In later PRs we'll move the existing fs code behind a "local"
implementation of this ThreadStore interface.

This PR should be a no-op behaviorally, it only introduces the
interface.

codex-rs/thread-store/src/store.rs

@@ -0,0 +1,65 @@
+use async_trait::async_trait;
+
+use crate::AppendThreadItemsParams;
+use crate::ArchiveThreadParams;
+use crate::CreateThreadParams;
+use crate::ListThreadsParams;
+use crate::LoadThreadHistoryParams;
+use crate::ReadThreadParams;
+use crate::ResumeThreadRecorderParams;
+use crate::SetThreadNameParams;
+use crate::StoredThread;
+use crate::StoredThreadHistory;
+use crate::ThreadPage;
+use crate::ThreadRecorder;
+use crate::ThreadStoreResult;
+use crate::UpdateThreadMetadataParams;
+
+/// Storage-neutral thread persistence boundary.
+#[async_trait]
+pub trait ThreadStore: Send + Sync {
+    /// Creates a new thread and returns a live recorder for future appends.
+    async fn create_thread(
+        &self,
+        params: CreateThreadParams,
+    ) -> ThreadStoreResult<Box<dyn ThreadRecorder>>;
+
+    /// Reopens a live recorder for an existing thread.
+    async fn resume_thread_recorder(
+        &self,
+        params: ResumeThreadRecorderParams,
+    ) -> ThreadStoreResult<Box<dyn ThreadRecorder>>;
+
+    /// Appends items to a stored thread outside the live-recorder path.
+    async fn append_items(&self, params: AppendThreadItemsParams) -> ThreadStoreResult<()>;
+
+    /// Loads persisted history for resume, fork, rollback, and memory jobs.
+    async fn load_history(
+        &self,
+        params: LoadThreadHistoryParams,
+    ) -> ThreadStoreResult<StoredThreadHistory>;
+
+    /// Reads a thread summary and optionally its persisted history.
+    async fn read_thread(&self, params: ReadThreadParams) -> ThreadStoreResult<StoredThread>;
+
+    /// Lists stored threads matching the supplied filters.
+    async fn list_threads(&self, params: ListThreadsParams) -> ThreadStoreResult<ThreadPage>;
+
+    /// Sets a user-facing thread name.
+    async fn set_thread_name(&self, params: SetThreadNameParams) -> ThreadStoreResult<()>;
+
+    /// Applies a mutable metadata patch and returns the updated thread.
+    async fn update_thread_metadata(
+        &self,
+        params: UpdateThreadMetadataParams,
+    ) -> ThreadStoreResult<StoredThread>;
+
+    /// Archives a thread.
+    async fn archive_thread(&self, params: ArchiveThreadParams) -> ThreadStoreResult<()>;
+
+    /// Unarchives a thread and returns its updated metadata.
+    async fn unarchive_thread(
+        &self,
+        params: ArchiveThreadParams,
+    ) -> ThreadStoreResult<StoredThread>;
+}