Prevent upstream 400 failures when clients omit prior
reasoning_content in multi-turn tool-calling conversations.
Capture reasoning_content from streaming and non-streaming assistant
responses, persist it in a memory-plus-SQLite cache keyed by
tool_call_id, and re-inject it on later requests when available.
Add the reasoning cache migration, service layer, authenticated API
endpoints, dashboard tab, and unit coverage to support inspection,
cleanup, and crash recovery.