`_orphan_timeout()` was `max(300, A2A_REPLY_TIMEOUT)` with no ceiling, so
an absurd value (1e18) meant the watchdog sweep could never fail an
orphan — the reply window is a floor for the grace, not a licence to
disable the sweep. Cap it at 86400s.
`disconnect()` failed and cleared `_pending`/`_pending_order` but left
`_active_tasks` populated, so a reconnected adapter would keep excluding
dead task ids from the orphan sweep forever. Clear it in the same locked
block.
138e426f62