Route async-delegation completions by the immutable origin_ui_session_id (exact origin tab) and deliver them through a durable claim/complete/release lifecycle so they arrive exactly once, restart-safe, on both the background wakeup and next-turn drain paths. Combines #6185 (@carlotestor) + #6159 (@sysophelper-droid); supersedes #6002/#6225.
Co-authored-by: carlotestor <carlotestor@users.noreply.github.com>
Co-authored-by: sysophelper-droid <sysophelper-droid@users.noreply.github.com>
