wait_for_release polled until the full timeout (10 min by default) even
when the holder never left AGENT, so an unseen request_handoff blocked the
turn instead of letting the model chase the user in chat. After `grace`
seconds (param, default 60, capped at the timeout) with the handoff still
pending and no human holding, return {ok: false, code: no_takeover}. Once
a human holds the screen the full timeout still applies to the hand-back.
(cherry picked from commit 1402af036044a7191ec885fc8fa5c24206880909)
4d886fa904