Under the hood
Submitting input records a timestamp and can override input mode, with a callback restoring a handed-back prompt.
The chat input submit handler now accepts an inputModeOverride option and records a submittedAtMs timestamp at submit time, passed through to downstream processing. A new restoreHandedBackPrompt callback, tied to rate-limit auto-continue, restores a previously handed-back prompt via consumeRateLimitAutoContinuePrefill().