Ensure list_threads drops stale rollout files (#11572)

Summary
- trim `state_db::list_threads_db` results to entries whose rollout
files still exist, logging and recording a discrepancy for dropped rows
- delete stale metadata rows from the SQLite store so future calls don’t
surface invalid paths
- add regression coverage in `recorder.rs` to verify stale DB paths are
dropped when the file is missing

codex-rs/state/src/runtime.rs

@@ -650,6 +650,15 @@ ON CONFLICT(thread_id, position) DO NOTHING
         self.upsert_thread(&metadata).await
     }
 
+    /// Delete a thread metadata row by id.
+    pub async fn delete_thread(&self, thread_id: ThreadId) -> anyhow::Result<u64> {
+        let result = sqlx::query("DELETE FROM threads WHERE id = ?")
+            .bind(thread_id.to_string())
+            .execute(self.pool.as_ref())
+            .await?;
+        Ok(result.rows_affected())
+    }
+
     async fn ensure_backfill_state_row(&self) -> anyhow::Result<()> {
         sqlx::query(
             r#"