chat_name keys the pinned session-context prompt, and the title lane
renames a new auto-thread once the LLM title arrives, normally before the
user's second message. Turn 2 read the new name and re-rendered the
already-sent prompt, a prompt-cache miss on every auto-threaded
conversation on the default config.
rename_thread now records the name it replaced and the name it set for a
guarded semantic rename, and _format_thread_chat_name keeps the replaced
name while the thread still carries Hermes's title. A rename by anyone
else no longer matches and re-renders as before.
(cherry picked from commit b57858e031b8af5f6fa3fa8d567907c16fafda2b)
ec991b468b