Allow setting daybreakEnabled when starting a thread (#45513)

## What changed

Add experimental `thread/start.daybreakEnabled` so clients can set the initial preference for persistent threads. Omitted or null values leave it unset; explicit values are rejected for ephemeral threads.

Return the choice in the start response, `thread/started`, and reads before persistence. Stage it with the initial thread metadata and save it when the thread is persisted. Later changes still use `thread/metadata/update`. The preference does not select `turn/start.cyberAccessProgram` or grant access.

## Testing

Add coverage for true, false, and unset values in responses, notifications, reads, and reads after persistence and restart, plus rejection for ephemeral threads. Update existing metadata and access-program tests to exercise threads with an initial preference.

GitOrigin-RevId: 3bff3dc55a18436067bc2a3f156f5abf52d7321b

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

@@ -481,6 +481,19 @@ impl ThreadStore for LocalThreadStore {
         })
     }
 
+    fn read_pending_thread_metadata(
+        &self,
+        thread_id: ThreadId,
+    ) -> ThreadStoreFuture<'_, Option<ThreadMetadataPatch>> {
+        Box::pin(async move {
+            Ok(self
+                .pending_thread_metadata
+                .lock(thread_id)
+                .await
+                .and_then(|metadata| metadata.clone()))
+        })
+    }
+
     fn remove_pending_thread_metadata(&self, thread_id: ThreadId) -> ThreadStoreFuture<'_, ()> {
         Box::pin(async move {
             self.pending_thread_metadata.remove(thread_id).await;

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

@@ -116,6 +116,14 @@ pub trait ThreadStore: Any + Send + Sync {
         })
     }
 
+    /// Reads metadata staged for a reserved thread without persisting it.
+    fn read_pending_thread_metadata(
+        &self,
+        _thread_id: ThreadId,
+    ) -> ThreadStoreFuture<'_, Option<ThreadMetadataPatch>> {
+        Box::pin(async { Ok(None) })
+    }
+
     /// Removes host-owned metadata staged for a reserved thread ID.
     fn remove_pending_thread_metadata(&self, _thread_id: ThreadId) -> ThreadStoreFuture<'_, ()> {
         Box::pin(async {