## Summary
Fix `getConversationSummary` so thread-id summaries work for stored
threads that do not have a local rollout path, such as remote thread
stores.
The root cause was that `summary_from_stored_thread` returned `None`
when `StoredThread.rollout_path` was absent, and
`get_thread_summary_response_inner` treated that as an internal error.
This made conversation-id lookups depend on a local-only field even
though the thread store can address the thread by id.
0274398901