Extracts two pure context helpers used during input-state assembly:
* mentioned_docs.format_mentioned_surfsense_docs_as_context: renders the
user's @-mentioned SurfSense docs into the LLM context block.
* deepagents_todos.extract_todos_from_deepagents: pulls the in-progress
todo list from a deep-agents state snapshot for the title generator.
Add-only; existing call sites in stream_new_chat.py remain untouched
until cutover.
