Whether the Transfer Manager panel is open.
All known transfers, keyed by transfer id.
Active transfers — queued or running.
Remove all transfers in a terminal state (done / failed / canceled).
Completed transfers — done, failed, or canceled.
Open the panel (idempotent).
Open the panel in minimized (pill) mode without taking focus.
Remove a transfer by id (e.g. after explicit dismiss).
Explicitly set the minimized state.
Toggle panel open/closed.
Whether the panel is minimized to the toolbar pill.